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How to write a review article?

In the medical sciences, the importance of review articles is rising. When clinicians want to update their knowledge and generate guidelines about a topic, they frequently use reviews as a starting point. The value of a review is associated with what has been done, what has been found and how these findings are presented. Before asking ‘how,’ the question of ‘why’ is more important when starting to write a review. The main and fundamental purpose of writing a review is to create a readable synthesis of the best resources available in the literature for an important research question or a current area of research. Although the idea of writing a review is attractive, it is important to spend time identifying the important questions. Good review methods are critical because they provide an unbiased point of view for the reader regarding the current literature. There is a consensus that a review should be written in a systematic fashion, a notion that is usually followed. In a systematic review with a focused question, the research methods must be clearly described. A ‘methodological filter’ is the best method for identifying the best working style for a research question, and this method reduces the workload when surveying the literature. An essential part of the review process is differentiating good research from bad and leaning on the results of the better studies. The ideal way to synthesize studies is to perform a meta-analysis. In conclusion, when writing a review, it is best to clearly focus on fixed ideas, to use a procedural and critical approach to the literature and to express your findings in an attractive way.

The importance of review articles in health sciences is increasing day by day. Clinicians frequently benefit from review articles to update their knowledge in their field of specialization, and use these articles as a starting point for formulating guidelines. [ 1 , 2 ] The institutions which provide financial support for further investigations resort to these reviews to reveal the need for these researches. [ 3 ] As is the case with all other researches, the value of a review article is related to what is achieved, what is found, and the way of communicating this information. A few studies have evaluated the quality of review articles. Murlow evaluated 50 review articles published in 1985, and 1986, and revealed that none of them had complied with clear-cut scientific criteria. [ 4 ] In 1996 an international group that analyzed articles, demonstrated the aspects of review articles, and meta-analyses that had not complied with scientific criteria, and elaborated QUOROM (QUality Of Reporting Of Meta-analyses) statement which focused on meta-analyses of randomized controlled studies. [ 5 ] Later on this guideline was updated, and named as PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses). [ 6 ]

Review articles are divided into 2 categories as narrative, and systematic reviews. Narrative reviews are written in an easily readable format, and allow consideration of the subject matter within a large spectrum. However in a systematic review, a very detailed, and comprehensive literature surveying is performed on the selected topic. [ 7 , 8 ] Since it is a result of a more detailed literature surveying with relatively lesser involvement of author’s bias, systematic reviews are considered as gold standard articles. Systematic reviews can be diivded into qualitative, and quantitative reviews. In both of them detailed literature surveying is performed. However in quantitative reviews, study data are collected, and statistically evaluated (ie. meta-analysis). [ 8 ]

Before inquring for the method of preparation of a review article, it is more logical to investigate the motivation behind writing the review article in question. The fundamental rationale of writing a review article is to make a readable synthesis of the best literature sources on an important research inquiry or a topic. This simple definition of a review article contains the following key elements:

• The question(s) to be dealt with
• Methods used to find out, and select the best quality researches so as to respond to these questions.
• To synthetize available, but quite different researches

For the specification of important questions to be answered, number of literature references to be consulted should be more or less determined. Discussions should be conducted with colleagues in the same area of interest, and time should be reserved for the solution of the problem(s). Though starting to write the review article promptly seems to be very alluring, the time you spend for the determination of important issues won’t be a waste of time. [ 9 ]

The PRISMA statement [ 6 ] elaborated to write a well-designed review articles contains a 27-item checklist ( Table 1 ). It will be reasonable to fulfill the requirements of these items during preparation of a review article or a meta-analysis. Thus preparation of a comprehensible article with a high-quality scientific content can be feasible.

PRISMA statement: A 27-item checklist

Contents and format

Important differences exist between systematic, and non-systematic reviews which especially arise from methodologies used in the description of the literature sources. A non-systematic review means use of articles collected for years with the recommendations of your colleagues, while systematic review is based on struggles to search for, and find the best possible researches which will respond to the questions predetermined at the start of the review.

Though a consensus has been reached about the systematic design of the review articles, studies revealed that most of them had not been written in a systematic format. McAlister et al. analyzed review articles in 6 medical journals, and disclosed that in less than one fourth of the review articles, methods of description, evaluation or synthesis of evidence had been provided, one third of them had focused on a clinical topic, and only half of them had provided quantitative data about the extend of the potential benefits. [ 10 ]

Use of proper methodologies in review articles is important in that readers assume an objective attitude towards updated information. We can confront two problems while we are using data from researches in order to answer certain questions. Firstly, we can be prejudiced during selection of research articles or these articles might be biased. To minimize this risk, methodologies used in our reviews should allow us to define, and use researches with minimal degree of bias. The second problem is that, most of the researches have been performed with small sample sizes. In statistical methods in meta-analyses, available researches are combined to increase the statistical power of the study. The problematic aspect of a non-systematic review is that our tendency to give biased responses to the questions, in other words we apt to select the studies with known or favourite results, rather than the best quality investigations among them.

As is the case with many research articles, general format of a systematic review on a single subject includes sections of Introduction, Methods, Results, and Discussion ( Table 2 ).

Structure of a systematic review

Preparation of the review article

Steps, and targets of constructing a good review article are listed in Table 3 . To write a good review article the items in Table 3 should be implemented step by step. [ 11 – 13 ]

Steps of a systematic review

The research question

It might be helpful to divide the research question into components. The most prevalently used format for questions related to the treatment is PICO (P - Patient, Problem or Population; I-Intervention; C-appropriate Comparisons, and O-Outcome measures) procedure. For example In female patients (P) with stress urinary incontinence, comparisons (C) between transobturator, and retropubic midurethral tension-free band surgery (I) as for patients’ satisfaction (O).

Finding Studies

In a systematic review on a focused question, methods of investigation used should be clearly specified.

Ideally, research methods, investigated databases, and key words should be described in the final report. Different databases are used dependent on the topic analyzed. In most of the clinical topics, Medline should be surveyed. However searching through Embase and CINAHL can be also appropriate.

While determining appropriate terms for surveying, PICO elements of the issue to be sought may guide the process. Since in general we are interested in more than one outcome, P, and I can be key elements. In this case we should think about synonyms of P, and I elements, and combine them with a conjunction AND.

One method which might alleviate the workload of surveying process is “methodological filter” which aims to find the best investigation method for each research question. A good example of this method can be found in PubMed interface of Medline. The Clinical Queries tool offers empirically developed filters for five different inquiries as guidelines for etiology, diagnosis, treatment, prognosis or clinical prediction.

Evaluation of the Quality of the Study

As an indispensable component of the review process is to discriminate good, and bad quality researches from each other, and the outcomes should be based on better qualified researches, as far as possible. To achieve this goal you should know the best possible evidence for each type of question The first component of the quality is its general planning/design of the study. General planning/design of a cohort study, a case series or normal study demonstrates variations.

A hierarchy of evidence for different research questions is presented in Table 4 . However this hierarchy is only a first step. After you find good quality research articles, you won’t need to read all the rest of other articles which saves you tons of time. [ 14 ]

Determination of levels of evidence based on the type of the research question

Formulating a Synthesis

Rarely all researches arrive at the same conclusion. In this case a solution should be found. However it is risky to make a decision based on the votes of absolute majority. Indeed, a well-performed large scale study, and a weakly designed one are weighed on the same scale. Therefore, ideally a meta-analysis should be performed to solve apparent differences. Ideally, first of all, one should be focused on the largest, and higher quality study, then other studies should be compared with this basic study.

Conclusions

In conclusion, during writing process of a review article, the procedures to be achieved can be indicated as follows: 1) Get rid of fixed ideas, and obsessions from your head, and view the subject from a large perspective. 2) Research articles in the literature should be approached with a methodological, and critical attitude and 3) finally data should be explained in an attractive way.

Review articles: purpose, process, and structure

• Published: 02 October 2017
• Volume 46 , pages 1–5, ( 2018 )

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• Robert W. Palmatier 1 ,
• Mark B. Houston 2 &
• John Hulland 3  

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Many research disciplines feature high-impact journals that are dedicated outlets for review papers (or review–conceptual combinations) (e.g., Academy of Management Review , Psychology Bulletin , Medicinal Research Reviews ). The rationale for such outlets is the premise that research integration and synthesis provides an important, and possibly even a required, step in the scientific process. Review papers tend to include both quantitative (i.e., meta-analytic, systematic reviews) and narrative or more qualitative components; together, they provide platforms for new conceptual frameworks, reveal inconsistencies in the extant body of research, synthesize diverse results, and generally give other scholars a “state-of-the-art” snapshot of a domain, often written by topic experts (Bem 1995 ). Many premier marketing journals publish meta-analytic review papers too, though authors often must overcome reviewers’ concerns that their contributions are limited due to the absence of “new data.” Furthermore, relatively few non-meta-analysis review papers appear in marketing journals, probably due to researchers’ perceptions that such papers have limited publication opportunities or their beliefs that the field lacks a research tradition or “respect” for such papers. In many cases, an editor must provide strong support to help such review papers navigate the review process. Yet, once published, such papers tend to be widely cited, suggesting that members of the field find them useful (see Bettencourt and Houston 2001 ).

In this editorial, we seek to address three topics relevant to review papers. First, we outline a case for their importance to the scientific process, by describing the purpose of review papers . Second, we detail the review paper editorial initiative conducted over the past two years by the Journal of the Academy of Marketing Science ( JAMS ), focused on increasing the prevalence of review papers. Third, we describe a process and structure for systematic ( i.e. , non-meta-analytic) review papers , referring to Grewal et al. ( 2018 ) insights into parallel meta-analytic (effects estimation) review papers. (For some strong recent examples of marketing-related meta-analyses, see Knoll and Matthes 2017 ; Verma et al. 2016 ).

Purpose of review papers

In their most general form, review papers “are critical evaluations of material that has already been published,” some that include quantitative effects estimation (i.e., meta-analyses) and some that do not (i.e., systematic reviews) (Bem 1995 , p. 172). They carefully identify and synthesize relevant literature to evaluate a specific research question, substantive domain, theoretical approach, or methodology and thereby provide readers with a state-of-the-art understanding of the research topic. Many of these benefits are highlighted in Hanssens’ ( 2018 ) paper titled “The Value of Empirical Generalizations in Marketing,” published in this same issue of JAMS.

The purpose of and contributions associated with review papers can vary depending on their specific type and research question, but in general, they aim to

Resolve definitional ambiguities and outline the scope of the topic.

Provide an integrated, synthesized overview of the current state of knowledge.

Identify inconsistencies in prior results and potential explanations (e.g., moderators, mediators, measures, approaches).

Evaluate existing methodological approaches and unique insights.

Develop conceptual frameworks to reconcile and extend past research.

Describe research insights, existing gaps, and future research directions.

Not every review paper can offer all of these benefits, but this list represents their key contributions. To provide a sufficient contribution, a review paper needs to achieve three key standards. First, the research domain needs to be well suited for a review paper, such that a sufficient body of past research exists to make the integration and synthesis valuable—especially if extant research reveals theoretical inconsistences or heterogeneity in its effects. Second, the review paper must be well executed, with an appropriate literature collection and analysis techniques, sufficient breadth and depth of literature coverage, and a compelling writing style. Third, the manuscript must offer significant new insights based on its systematic comparison of multiple studies, rather than simply a “book report” that describes past research. This third, most critical standard is often the most difficult, especially for authors who have not “lived” with the research domain for many years, because achieving it requires drawing some non-obvious connections and insights from multiple studies and their many different aspects (e.g., context, method, measures). Typically, after the “review” portion of the paper has been completed, the authors must spend many more months identifying the connections to uncover incremental insights, each of which takes time to detail and explicate.

The increasing methodological rigor and technical sophistication of many marketing studies also means that they often focus on smaller problems with fewer constructs. By synthesizing these piecemeal findings, reconciling conflicting evidence, and drawing a “big picture,” meta-analyses and systematic review papers become indispensable to our comprehensive understanding of a phenomenon, among both academic and practitioner communities. Thus, good review papers provide a solid platform for future research, in the reviewed domain but also in other areas, in that researchers can use a good review paper to learn about and extend key insights to new areas.

This domain extension, outside of the core area being reviewed, is one of the key benefits of review papers that often gets overlooked. Yet it also is becoming ever more important with the expanding breadth of marketing (e.g., econometric modeling, finance, strategic management, applied psychology, sociology) and the increasing velocity in the accumulation of marketing knowledge (e.g., digital marketing, social media, big data). Against this backdrop, systematic review papers and meta-analyses help academics and interested managers keep track of research findings that fall outside their main area of specialization.

JAMS’ review paper editorial initiative

With a strong belief in the importance of review papers, the editorial team of JAMS has purposely sought out leading scholars to provide substantive review papers, both meta-analysis and systematic, for publication in JAMS . Many of the scholars approached have voiced concerns about the risk of such endeavors, due to the lack of alternative outlets for these types of papers. Therefore, we have instituted a unique process, in which the authors develop a detailed outline of their paper, key tables and figures, and a description of their literature review process. On the basis of this outline, we grant assurances that the contribution hurdle will not be an issue for publication in JAMS , as long as the authors execute the proposed outline as written. Each paper still goes through the normal review process and must meet all publication quality standards, of course. In many cases, an Area Editor takes an active role to help ensure that each paper provides sufficient insights, as required for a high-quality review paper. This process gives the author team confidence to invest effort in the process. An analysis of the marketing journals in the Financial Times (FT 50) journal list for the past five years (2012–2016) shows that JAMS has become the most common outlet for these papers, publishing 31% of all review papers that appeared in the top six marketing journals.

As a next step in positioning JAMS as a receptive marketing outlet for review papers, we are conducting a Thought Leaders Conference on Generalizations in Marketing: Systematic Reviews and Meta-Analyses , with a corresponding special issue (see www.springer.com/jams ). We will continue our process of seeking out review papers as an editorial strategy in areas that could be advanced by the integration and synthesis of extant research. We expect that, ultimately, such efforts will become unnecessary, as authors initiate review papers on topics of their own choosing to submit them to JAMS . In the past two years, JAMS already has increased the number of papers it publishes annually, from just over 40 to around 60 papers per year; this growth has provided “space” for 8–10 review papers per year, reflecting our editorial target.

Consistent with JAMS ’ overall focus on managerially relevant and strategy-focused topics, all review papers should reflect this emphasis. For example, the domains, theories, and methods reviewed need to have some application to past or emerging managerial research. A good rule of thumb is that the substantive domain, theory, or method should attract the attention of readers of JAMS .

The efforts of multiple editors and Area Editors in turn have generated a body of review papers that can serve as useful examples of the different types and approaches that JAMS has published.

Domain-based review papers

Domain-based review papers review, synthetize, and extend a body of literature in the same substantive domain. For example, in “The Role of Privacy in Marketing” (Martin and Murphy 2017 ), the authors identify and define various privacy-related constructs that have appeared in recent literature. Then they examine the different theoretical perspectives brought to bear on privacy topics related to consumers and organizations, including ethical and legal perspectives. These foundations lead in to their systematic review of privacy-related articles over a clearly defined date range, from which they extract key insights from each study. This exercise of synthesizing diverse perspectives allows these authors to describe state-of-the-art knowledge regarding privacy in marketing and identify useful paths for research. Similarly, a new paper by Cleeren et al. ( 2017 ), “Marketing Research on Product-Harm Crises: A Review, Managerial Implications, and an Agenda for Future Research,” provides a rich systematic review, synthesizes extant research, and points the way forward for scholars who are interested in issues related to defective or dangerous market offerings.

Theory-based review papers

Theory-based review papers review, synthetize, and extend a body of literature that uses the same underlying theory. For example, Rindfleisch and Heide’s ( 1997 ) classic review of research in marketing using transaction cost economics has been cited more than 2200 times, with a significant impact on applications of the theory to the discipline in the past 20 years. A recent paper in JAMS with similar intent, which could serve as a helpful model, focuses on “Resource-Based Theory in Marketing” (Kozlenkova et al. 2014 ). The article dives deeply into a description of the theory and its underlying assumptions, then organizes a systematic review of relevant literature according to various perspectives through which the theory has been applied in marketing. The authors conclude by identifying topical domains in marketing that might benefit from additional applications of the theory (e.g., marketing exchange), as well as related theories that could be integrated meaningfully with insights from the resource-based theory.

Method-based review papers

Method-based review papers review, synthetize, and extend a body of literature that uses the same underlying method. For example, in “Event Study Methodology in the Marketing Literature: An Overview” (Sorescu et al. 2017 ), the authors identify published studies in marketing that use an event study methodology. After a brief review of the theoretical foundations of event studies, they describe in detail the key design considerations associated with this method. The article then provides a roadmap for conducting event studies and compares this approach with a stock market returns analysis. The authors finish with a summary of the strengths and weaknesses of the event study method, which in turn suggests three main areas for further research. Similarly, “Discriminant Validity Testing in Marketing: An Analysis, Causes for Concern, and Proposed Remedies” (Voorhies et al. 2016 ) systematically reviews existing approaches for assessing discriminant validity in marketing contexts, then uses Monte Carlo simulation to determine which tests are most effective.

Our long-term editorial strategy is to make sure JAMS becomes and remains a well-recognized outlet for both meta-analysis and systematic managerial review papers in marketing. Ideally, review papers would come to represent 10%–20% of the papers published by the journal.

Process and structure for review papers

In this section, we review the process and typical structure of a systematic review paper, which lacks any long or established tradition in marketing research. The article by Grewal et al. ( 2018 ) provides a summary of effects-focused review papers (i.e., meta-analyses), so we do not discuss them in detail here.

Systematic literature review process

Some review papers submitted to journals take a “narrative” approach. They discuss current knowledge about a research domain, yet they often are flawed, in that they lack criteria for article inclusion (or, more accurately, article exclusion), fail to discuss the methodology used to evaluate included articles, and avoid critical assessment of the field (Barczak 2017 ). Such reviews tend to be purely descriptive, with little lasting impact.

In contrast, a systematic literature review aims to “comprehensively locate and synthesize research that bears on a particular question, using organized, transparent, and replicable procedures at each step in the process” (Littell et al. 2008 , p. 1). Littell et al. describe six key steps in the systematic review process. The extent to which each step is emphasized varies by paper, but all are important components of the review.

Topic formulation . The author sets out clear objectives for the review and articulates the specific research questions or hypotheses that will be investigated.

Study design . The author specifies relevant problems, populations, constructs, and settings of interest. The aim is to define explicit criteria that can be used to assess whether any particular study should be included in or excluded from the review. Furthermore, it is important to develop a protocol in advance that describes the procedures and methods to be used to evaluate published work.

Sampling . The aim in this third step is to identify all potentially relevant studies, including both published and unpublished research. To this end, the author must first define the sampling unit to be used in the review (e.g., individual, strategic business unit) and then develop an appropriate sampling plan.

Data collection . By retrieving the potentially relevant studies identified in the third step, the author can determine whether each study meets the eligibility requirements set out in the second step. For studies deemed acceptable, the data are extracted from each study and entered into standardized templates. These templates should be based on the protocols established in step 2.

Data analysis . The degree and nature of the analyses used to describe and examine the collected data vary widely by review. Purely descriptive analysis is useful as a starting point but rarely is sufficient on its own. The examination of trends, clusters of ideas, and multivariate relationships among constructs helps flesh out a deeper understanding of the domain. For example, both Hult ( 2015 ) and Huber et al. ( 2014 ) use bibliometric approaches (e.g., examine citation data using multidimensional scaling and cluster analysis techniques) to identify emerging versus declining themes in the broad field of marketing.

Reporting . Three key aspects of this final step are common across systematic reviews. First, the results from the fifth step need to be presented, clearly and compellingly, using narratives, tables, and figures. Second, core results that emerge from the review must be interpreted and discussed by the author. These revelatory insights should reflect a deeper understanding of the topic being investigated, not simply a regurgitation of well-established knowledge. Third, the author needs to describe the implications of these unique insights for both future research and managerial practice.

A new paper by Watson et al. ( 2017 ), “Harnessing Difference: A Capability-Based Framework for Stakeholder Engagement in Environmental Innovation,” provides a good example of a systematic review, starting with a cohesive conceptual framework that helps establish the boundaries of the review while also identifying core constructs and their relationships. The article then explicitly describes the procedures used to search for potentially relevant papers and clearly sets out criteria for study inclusion or exclusion. Next, a detailed discussion of core elements in the framework weaves published research findings into the exposition. The paper ends with a presentation of key implications and suggestions for the next steps. Similarly, “Marketing Survey Research Best Practices: Evidence and Recommendations from a Review of JAMS Articles” (Hulland et al. 2017 ) systematically reviews published marketing studies that use survey techniques, describes recent trends, and suggests best practices. In their review, Hulland et al. examine the entire population of survey papers published in JAMS over a ten-year span, relying on an extensive standardized data template to facilitate their subsequent data analysis.

Structure of systematic review papers

There is no cookie-cutter recipe for the exact structure of a useful systematic review paper; the final structure depends on the authors’ insights and intended points of emphasis. However, several key components are likely integral to a paper’s ability to contribute.

Depth and rigor

Systematic review papers must avoid falling in to two potential “ditches.” The first ditch threatens when the paper fails to demonstrate that a systematic approach was used for selecting articles for inclusion and capturing their insights. If a reader gets the impression that the author has cherry-picked only articles that fit some preset notion or failed to be thorough enough, without including articles that make significant contributions to the field, the paper will be consigned to the proverbial side of the road when it comes to the discipline’s attention.

Authors that fall into the other ditch present a thorough, complete overview that offers only a mind-numbing recitation, without evident organization, synthesis, or critical evaluation. Although comprehensive, such a paper is more of an index than a useful review. The reviewed articles must be grouped in a meaningful way to guide the reader toward a better understanding of the focal phenomenon and provide a foundation for insights about future research directions. Some scholars organize research by scholarly perspectives (e.g., the psychology of privacy, the economics of privacy; Martin and Murphy 2017 ); others classify the chosen articles by objective research aspects (e.g., empirical setting, research design, conceptual frameworks; Cleeren et al. 2017 ). The method of organization chosen must allow the author to capture the complexity of the underlying phenomenon (e.g., including temporal or evolutionary aspects, if relevant).

Replicability

Processes for the identification and inclusion of research articles should be described in sufficient detail, such that an interested reader could replicate the procedure. The procedures used to analyze chosen articles and extract their empirical findings and/or key takeaways should be described with similar specificity and detail.

We already have noted the potential usefulness of well-done review papers. Some scholars always are new to the field or domain in question, so review papers also need to help them gain foundational knowledge. Key constructs, definitions, assumptions, and theories should be laid out clearly (for which purpose summary tables are extremely helpful). An integrated conceptual model can be useful to organize cited works. Most scholars integrate the knowledge they gain from reading the review paper into their plans for future research, so it is also critical that review papers clearly lay out implications (and specific directions) for research. Ideally, readers will come away from a review article filled with enthusiasm about ways they might contribute to the ongoing development of the field.

Helpful format

Because such a large body of research is being synthesized in most review papers, simply reading through the list of included studies can be exhausting for readers. We cannot overstate the importance of tables and figures in review papers, used in conjunction with meaningful headings and subheadings. Vast literature review tables often are essential, but they must be organized in a way that makes their insights digestible to the reader; in some cases, a sequence of more focused tables may be better than a single, comprehensive table.

In summary, articles that review extant research in a domain (topic, theory, or method) can be incredibly useful to the scientific progress of our field. Whether integrating the insights from extant research through a meta-analysis or synthesizing them through a systematic assessment, the promised benefits are similar. Both formats provide readers with a useful overview of knowledge about the focal phenomenon, as well as insights on key dilemmas and conflicting findings that suggest future research directions. Thus, the editorial team at JAMS encourages scholars to continue to invest the time and effort to construct thoughtful review papers.

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Palmatier, R.W., Houston, M.B. & Hulland, J. Review articles: purpose, process, and structure. J. of the Acad. Mark. Sci. 46 , 1–5 (2018). https://doi.org/10.1007/s11747-017-0563-4

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Published : 02 October 2017

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DOI : https://doi.org/10.1007/s11747-017-0563-4

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A literature review is a document or section of a document that collects key sources on a topic and discusses those sources in conversation with each other (also called synthesis ). The lit review is an important genre in many disciplines, not just literature (i.e., the study of works of literature such as novels and plays). When we say “literature review” or refer to “the literature,” we are talking about the research ( scholarship ) in a given field. You will often see the terms “the research,” “the scholarship,” and “the literature” used mostly interchangeably.

Where, when, and why would I write a lit review?

There are a number of different situations where you might write a literature review, each with slightly different expectations; different disciplines, too, have field-specific expectations for what a literature review is and does. For instance, in the humanities, authors might include more overt argumentation and interpretation of source material in their literature reviews, whereas in the sciences, authors are more likely to report study designs and results in their literature reviews; these differences reflect these disciplines’ purposes and conventions in scholarship. You should always look at examples from your own discipline and talk to professors or mentors in your field to be sure you understand your discipline’s conventions, for literature reviews as well as for any other genre.

A literature review can be a part of a research paper or scholarly article, usually falling after the introduction and before the research methods sections. In these cases, the lit review just needs to cover scholarship that is important to the issue you are writing about; sometimes it will also cover key sources that informed your research methodology.

Lit reviews can also be standalone pieces, either as assignments in a class or as publications. In a class, a lit review may be assigned to help students familiarize themselves with a topic and with scholarship in their field, get an idea of the other researchers working on the topic they’re interested in, find gaps in existing research in order to propose new projects, and/or develop a theoretical framework and methodology for later research. As a publication, a lit review usually is meant to help make other scholars’ lives easier by collecting and summarizing, synthesizing, and analyzing existing research on a topic. This can be especially helpful for students or scholars getting into a new research area, or for directing an entire community of scholars toward questions that have not yet been answered.

What are the parts of a lit review?

Most lit reviews use a basic introduction-body-conclusion structure; if your lit review is part of a larger paper, the introduction and conclusion pieces may be just a few sentences while you focus most of your attention on the body. If your lit review is a standalone piece, the introduction and conclusion take up more space and give you a place to discuss your goals, research methods, and conclusions separately from where you discuss the literature itself.

Introduction:

• An introductory paragraph that explains what your working topic and thesis is
• A forecast of key topics or texts that will appear in the review
• Potentially, a description of how you found sources and how you analyzed them for inclusion and discussion in the review (more often found in published, standalone literature reviews than in lit review sections in an article or research paper)
• Summarize and synthesize: Give an overview of the main points of each source and combine them into a coherent whole
• Analyze and interpret: Don’t just paraphrase other researchers – add your own interpretations where possible, discussing the significance of findings in relation to the literature as a whole
• Critically Evaluate: Mention the strengths and weaknesses of your sources
• Write in well-structured paragraphs: Use transition words and topic sentence to draw connections, comparisons, and contrasts.

Conclusion:

• Summarize the key findings you have taken from the literature and emphasize their significance
• Connect it back to your primary research question

How should I organize my lit review?

Lit reviews can take many different organizational patterns depending on what you are trying to accomplish with the review. Here are some examples:

• Chronological : The simplest approach is to trace the development of the topic over time, which helps familiarize the audience with the topic (for instance if you are introducing something that is not commonly known in your field). If you choose this strategy, be careful to avoid simply listing and summarizing sources in order. Try to analyze the patterns, turning points, and key debates that have shaped the direction of the field. Give your interpretation of how and why certain developments occurred (as mentioned previously, this may not be appropriate in your discipline — check with a teacher or mentor if you’re unsure).
• Thematic : If you have found some recurring central themes that you will continue working with throughout your piece, you can organize your literature review into subsections that address different aspects of the topic. For example, if you are reviewing literature about women and religion, key themes can include the role of women in churches and the religious attitude towards women.
• Qualitative versus quantitative research
• Empirical versus theoretical scholarship
• Divide the research by sociological, historical, or cultural sources
• Theoretical : In many humanities articles, the literature review is the foundation for the theoretical framework. You can use it to discuss various theories, models, and definitions of key concepts. You can argue for the relevance of a specific theoretical approach or combine various theorical concepts to create a framework for your research.

What are some strategies or tips I can use while writing my lit review?

Any lit review is only as good as the research it discusses; make sure your sources are well-chosen and your research is thorough. Don’t be afraid to do more research if you discover a new thread as you’re writing. More info on the research process is available in our "Conducting Research" resources .

As you’re doing your research, create an annotated bibliography ( see our page on the this type of document ). Much of the information used in an annotated bibliography can be used also in a literature review, so you’ll be not only partially drafting your lit review as you research, but also developing your sense of the larger conversation going on among scholars, professionals, and any other stakeholders in your topic.

Usually you will need to synthesize research rather than just summarizing it. This means drawing connections between sources to create a picture of the scholarly conversation on a topic over time. Many student writers struggle to synthesize because they feel they don’t have anything to add to the scholars they are citing; here are some strategies to help you:

• It often helps to remember that the point of these kinds of syntheses is to show your readers how you understand your research, to help them read the rest of your paper.
• Writing teachers often say synthesis is like hosting a dinner party: imagine all your sources are together in a room, discussing your topic. What are they saying to each other?
• Look at the in-text citations in each paragraph. Are you citing just one source for each paragraph? This usually indicates summary only. When you have multiple sources cited in a paragraph, you are more likely to be synthesizing them (not always, but often
• Read more about synthesis here.

The most interesting literature reviews are often written as arguments (again, as mentioned at the beginning of the page, this is discipline-specific and doesn’t work for all situations). Often, the literature review is where you can establish your research as filling a particular gap or as relevant in a particular way. You have some chance to do this in your introduction in an article, but the literature review section gives a more extended opportunity to establish the conversation in the way you would like your readers to see it. You can choose the intellectual lineage you would like to be part of and whose definitions matter most to your thinking (mostly humanities-specific, but this goes for sciences as well). In addressing these points, you argue for your place in the conversation, which tends to make the lit review more compelling than a simple reporting of other sources.

How to write a good scientific review article

Affiliation.

• 1 The FEBS Journal Editorial Office, Cambridge, UK.
• PMID: 35792782
• DOI: 10.1111/febs.16565

Literature reviews are valuable resources for the scientific community. With research accelerating at an unprecedented speed in recent years and more and more original papers being published, review articles have become increasingly important as a means to keep up to date with developments in a particular area of research. A good review article provides readers with an in-depth understanding of a field and highlights key gaps and challenges to address with future research. Writing a review article also helps to expand the writer's knowledge of their specialist area and to develop their analytical and communication skills, amongst other benefits. Thus, the importance of building review-writing into a scientific career cannot be overstated. In this instalment of The FEBS Journal's Words of Advice series, I provide detailed guidance on planning and writing an informative and engaging literature review.

© 2022 Federation of European Biochemical Societies.

Publication types

• Review Literature as Topic*

Review Paper Format: How To Write A Review Article Fast

This guide aims to demystify the review paper format, presenting practical tips to help you accelerate the writing process. 

From understanding the structure to synthesising literature effectively, we’ll explore how to create a compelling review article swiftly, ensuring your work is both impactful and timely.

Whether you’re a seasoned researcher or a budding scholar, these insights will streamline your writing journey.

Research Paper, Review Paper Format

What is a review paper.

Diving into the realm of scholarly communication, you might have stumbled upon a research review article.

This unique genre serves to synthesise existing data, offering a panoramic view of the current state of knowledge on a particular topic. 

Unlike a standard research article that presents original experiments, a review paper delves into published literature, aiming to: 

• clarify, and
• evaluate previous findings.

Imagine you’re tasked to write a review article. The starting point is often a burning research question. Your mission? To scour various journals, piecing together a well-structured narrative that not only summarises key findings but also identifies gaps in existing literature.

This is where the magic of review writing shines – it’s about creating a roadmap for future research, highlighting areas ripe for exploration.

Review articles come in different flavours, with systematic reviews and meta-analyses being the gold standards. The methodology here is meticulous, with a clear protocol for selecting and evaluating studies.

This rigorous approach ensures that your review is more than just an overview; it’s a critical analysis that adds depth to the understanding of the subject.

Crafting a good review requires mastering the art of citation. Every claim or observation you make needs to be backed by relevant literature. This not only lends credibility to your work but also provides a treasure trove of information for readers eager to delve deeper.

Types Of Review Paper

Not all review articles are created equal. Each type has its methodology, purpose, and format, catering to different research needs and questions.

Systematic Review Paper

First up is the systematic review, the crème de la crème of review types. It’s known for its rigorous methodology, involving a detailed plan for:

• identifying,
• selecting, and
• critically appraising relevant research. 

The aim? To answer a specific research question. Systematic reviews often include meta-analyses, where data from multiple studies are statistically combined to provide more robust conclusions. This review type is a cornerstone in evidence-based fields like healthcare.

Literature Review Paper

Then there’s the literature review, a broader type you might encounter.

Here, the goal is to give an overview of the main points and debates on a topic, without the stringent methodological framework of a systematic review.

Literature reviews are great for getting a grasp of the field and identifying where future research might head. Often reading literature review papers can help you to learn about a topic rather quickly.

Narrative Reviews

Narrative reviews allow for a more flexible approach. Authors of narrative reviews draw on existing literature to provide insights or critique a certain area of research.

This is generally done with a less formal structure than systematic reviews. This type is particularly useful for areas where it’s difficult to quantify findings across studies.

Scoping Reviews

Scoping reviews are gaining traction for their ability to map out the existing literature on a broad topic, identifying:

• key concepts,
• theories, and

Unlike systematic reviews, scoping reviews have a more exploratory approach, which can be particularly useful in emerging fields or for topics that haven’t been comprehensively reviewed before.

Each type of review serves a unique purpose and requires a specific skill set. Whether you’re looking to summarise existing findings, synthesise data for evidence-based practice, or explore new research territories, there’s a review type that fits the bill. 

Knowing how to write, read, and interpret these reviews can significantly enhance your understanding of any research area.

What Are The Parts In A Review Paper

A review paper has a pretty set structure, with minor changes here and there to suit the topic covered. The format not only organises your thoughts but also guides your readers through the complexities of your topic.

Title & Abstract

Starting with the title and abstract, you set the stage. The title should be a concise indicator of the content, making it easier for others to quickly tell what your article content is about.

As for the abstract, it should act as a descriptive summary, offering a snapshot of your review’s scope and findings. 

Introduction

The introduction lays the groundwork, presenting the research question that drives your review. It’s here you:

• justify the importance of your review,
• delineating the current state of knowledge and
• highlighting gaps.

This section aims to articulate the significance of the topic and your objective in exploring it.

Methodology

The methodology section is the backbone of systematic reviews and meta-analyses, detailing the research methods employed to select, assess, and synthesise studies. 

This transparency allows readers to gauge the rigour and reproducibility of your review. It’s a testament to the integrity of your work, showing how you’ve minimised bias.

The heart of your review lies in the body, where you:

• analyse, and
• critique existing literature.

This is where you synthesise evidence, draw connections, and present both sides of any argument. Well-structured paragraphs and clear subheadings guide readers through your analysis, offering insights and fostering a deeper understanding of the subject.

Discussion & Conclusion

The discussion or conclusion section is where you weave together the main points, reflecting on what your findings mean for the field.

It’s about connecting the dots, offering a synthesis of evidence that answers your initial research question. This part often hints at future research directions, suggesting areas that need further exploration due to gaps in existing knowledge.

Lastly, the citation list is your nod to the scholarly community, acknowledging the contributions of others. Each citation is a thread in the larger tapestry of academic discourse, enabling readers to delve deeper into the research that has shaped your review.

Tips To Write An Review Article Fast

Writing a review article quickly without sacrificing quality might seem like a tall order, but with the right approach, it’s entirely achievable. 

Clearly Define Your Research Question

Clearly define your research question. A focused question not only narrows down the scope of your literature search but also keeps your review concise and on track.

By honing in on a specific aspect of a broader topic, you can avoid the common pitfall of becoming overwhelmed by the vast expanse of available literature. This specificity allows you to zero in on the most relevant studies, making your review more impactful.

Efficient Literature Searching

Utilise databases specific to your field and employ advanced search techniques like Boolean operators. This can drastically reduce the time you spend sifting through irrelevant articles.

Additionally, leveraging citation chains—looking at who has cited a pivotal paper in your area and who it cites—can uncover valuable sources you might otherwise miss.

Organise Your Findings Systematically

Developing a robust organisation strategy is key. As you gather sources, categorize them based on themes or methodologies. This not only aids in structuring your review but also in identifying areas where research is lacking or abundant.

Tools like citation management software can be invaluable here, helping you keep track of your sources and their key points. We list out some of the best AI tools for academic research here. 

Build An Outline Before Writing

Don’t underestimate the power of a well-structured outline. A clear blueprint of your article can guide your writing process, ensuring that each section flows logically into the next.

This roadmap not only speeds up the writing process by providing a clear direction but also helps maintain coherence, ensuring your review article delivers a compelling narrative that advances understanding in your field.

Start Writing With The Easiest Sections

When it’s time to write, start with sections you find easiest. This might be the methodology or a particular thematic section where you feel most confident.

Getting words on the page can build momentum, making it easier to tackle more challenging sections later.

Remember, your first draft doesn’t have to be perfect; the goal is to start articulating your synthesis of the literature.

Learn How To Write An Article Review

Mastering the review paper format is a crucial step towards efficient academic writing. By adhering to the structured components outlined, you can streamline the creation of a compelling review article.

Embracing these guidelines not only speeds up the writing process but also enhances the clarity and impact of your work, ensuring your contributions to scholarly discourse are both valuable and timely.

Dr Andrew Stapleton has a Masters and PhD in Chemistry from the UK and Australia. He has many years of research experience and has worked as a Postdoctoral Fellow and Associate at a number of Universities. Although having secured funding for his own research, he left academia to help others with his YouTube channel all about the inner workings of academia and how to make it work for you.

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Page Content

Overview of the review report format, the first read-through, first read considerations, spotting potential major flaws, concluding the first reading, rejection after the first reading, before starting the second read-through, doing the second read-through, the second read-through: section by section guidance, how to structure your report, on presentation and style, criticisms & confidential comments to editors, the recommendation, when recommending rejection, additional resources, step by step guide to reviewing a manuscript.

When you receive an invitation to peer review, you should be sent a copy of the paper's abstract to help you decide whether you wish to do the review. Try to respond to invitations promptly - it will prevent delays. It is also important at this stage to declare any potential Conflict of Interest.

The structure of the review report varies between journals. Some follow an informal structure, while others have a more formal approach.

" Number your comments!!! " (Jonathon Halbesleben, former Editor of Journal of Occupational and Organizational Psychology)

Informal Structure

Many journals don't provide criteria for reviews beyond asking for your 'analysis of merits'. In this case, you may wish to familiarize yourself with examples of other reviews done for the journal, which the editor should be able to provide or, as you gain experience, rely on your own evolving style.

Formal Structure

Other journals require a more formal approach. Sometimes they will ask you to address specific questions in your review via a questionnaire. Or they might want you to rate the manuscript on various attributes using a scorecard. Often you can't see these until you log in to submit your review. So when you agree to the work, it's worth checking for any journal-specific guidelines and requirements. If there are formal guidelines, let them direct the structure of your review.

In Both Cases

Whether specifically required by the reporting format or not, you should expect to compile comments to authors and possibly confidential ones to editors only.

Following the invitation to review, when you'll have received the article abstract, you should already understand the aims, key data and conclusions of the manuscript. If you don't, make a note now that you need to feedback on how to improve those sections.

The first read-through is a skim-read. It will help you form an initial impression of the paper and get a sense of whether your eventual recommendation will be to accept or reject the paper.

Keep a pen and paper handy when skim-reading.

Try to bear in mind the following questions - they'll help you form your overall impression:

• What is the main question addressed by the research? Is it relevant and interesting?
• How original is the topic? What does it add to the subject area compared with other published material?
• Is the paper well written? Is the text clear and easy to read?
• Are the conclusions consistent with the evidence and arguments presented? Do they address the main question posed?
• If the author is disagreeing significantly with the current academic consensus, do they have a substantial case? If not, what would be required to make their case credible?
• If the paper includes tables or figures, what do they add to the paper? Do they aid understanding or are they superfluous?

While you should read the whole paper, making the right choice of what to read first can save time by flagging major problems early on.

Editors say, " Specific recommendations for remedying flaws are VERY welcome ."

Examples of possibly major flaws include:

• Drawing a conclusion that is contradicted by the author's own statistical or qualitative evidence
• The use of a discredited method
• Ignoring a process that is known to have a strong influence on the area under study

If experimental design features prominently in the paper, first check that the methodology is sound - if not, this is likely to be a major flaw.

You might examine:

• The sampling in analytical papers
• The sufficient use of control experiments
• The precision of process data
• The regularity of sampling in time-dependent studies
• The validity of questions, the use of a detailed methodology and the data analysis being done systematically (in qualitative research)
• That qualitative research extends beyond the author's opinions, with sufficient descriptive elements and appropriate quotes from interviews or focus groups

Major Flaws in Information

If methodology is less of an issue, it's often a good idea to look at the data tables, figures or images first. Especially in science research, it's all about the information gathered. If there are critical flaws in this, it's very likely the manuscript will need to be rejected. Such issues include:

• Insufficient data
• Unclear data tables
• Contradictory data that either are not self-consistent or disagree with the conclusions
• Confirmatory data that adds little, if anything, to current understanding - unless strong arguments for such repetition are made

If you find a major problem, note your reasoning and clear supporting evidence (including citations).

After the initial read and using your notes, including those of any major flaws you found, draft the first two paragraphs of your review - the first summarizing the research question addressed and the second the contribution of the work. If the journal has a prescribed reporting format, this draft will still help you compose your thoughts.

The First Paragraph

This should state the main question addressed by the research and summarize the goals, approaches, and conclusions of the paper. It should:

• Help the editor properly contextualize the research and add weight to your judgement
• Show the author what key messages are conveyed to the reader, so they can be sure they are achieving what they set out to do
• Focus on successful aspects of the paper so the author gets a sense of what they've done well

The Second Paragraph

This should provide a conceptual overview of the contribution of the research. So consider:

• Is the paper's premise interesting and important?
• Are the methods used appropriate?
• Do the data support the conclusions?

After drafting these two paragraphs, you should be in a position to decide whether this manuscript is seriously flawed and should be rejected (see the next section). Or whether it is publishable in principle and merits a detailed, careful read through.

Even if you are coming to the opinion that an article has serious flaws, make sure you read the whole paper. This is very important because you may find some really positive aspects that can be communicated to the author. This could help them with future submissions.

A full read-through will also make sure that any initial concerns are indeed correct and fair. After all, you need the context of the whole paper before deciding to reject. If you still intend to recommend rejection, see the section "When recommending rejection."

Once the paper has passed your first read and you've decided the article is publishable in principle, one purpose of the second, detailed read-through is to help prepare the manuscript for publication. You may still decide to recommend rejection following a second reading.

" Offer clear suggestions for how the authors can address the concerns raised. In other words, if you're going to raise a problem, provide a solution ." (Jonathon Halbesleben, Editor of Journal of Occupational and Organizational Psychology)

Preparation

To save time and simplify the review:

• Don't rely solely upon inserting comments on the manuscript document - make separate notes
• Try to group similar concerns or praise together
• If using a review program to note directly onto the manuscript, still try grouping the concerns and praise in separate notes - it helps later
• Note line numbers of text upon which your notes are based - this helps you find items again and also aids those reading your review

Now that you have completed your preparations, you're ready to spend an hour or so reading carefully through the manuscript.

As you're reading through the manuscript for a second time, you'll need to keep in mind the argument's construction, the clarity of the language and content.

With regard to the argument’s construction, you should identify:

• Any places where the meaning is unclear or ambiguous
• Any factual errors
• Any invalid arguments

You may also wish to consider:

• Does the title properly reflect the subject of the paper?
• Does the abstract provide an accessible summary of the paper?
• Do the keywords accurately reflect the content?
• Is the paper an appropriate length?
• Are the key messages short, accurate and clear?

Not every submission is well written. Part of your role is to make sure that the text’s meaning is clear.

Editors say, " If a manuscript has many English language and editing issues, please do not try and fix it. If it is too bad, note that in your review and it should be up to the authors to have the manuscript edited ."

If the article is difficult to understand, you should have rejected it already. However, if the language is poor but you understand the core message, see if you can suggest improvements to fix the problem:

• Are there certain aspects that could be communicated better, such as parts of the discussion?
• Should the authors consider resubmitting to the same journal after language improvements?
• Would you consider looking at the paper again once these issues are dealt with?

On Grammar and Punctuation

Your primary role is judging the research content. Don't spend time polishing grammar or spelling. Editors will make sure that the text is at a high standard before publication. However, if you spot grammatical errors that affect clarity of meaning, then it's important to highlight these. Expect to suggest such amendments - it's rare for a manuscript to pass review with no corrections.

A 2010 study of nursing journals found that 79% of recommendations by reviewers were influenced by grammar and writing style (Shattel, et al., 2010).

1. The Introduction

A well-written introduction:

• Sets out the argument
• Summarizes recent research related to the topic
• Highlights gaps in current understanding or conflicts in current knowledge
• Establishes the originality of the research aims by demonstrating the need for investigations in the topic area
• Gives a clear idea of the target readership, why the research was carried out and the novelty and topicality of the manuscript

Originality and Topicality

Originality and topicality can only be established in the light of recent authoritative research. For example, it's impossible to argue that there is a conflict in current understanding by referencing articles that are 10 years old.

Authors may make the case that a topic hasn't been investigated in several years and that new research is required. This point is only valid if researchers can point to recent developments in data gathering techniques or to research in indirectly related fields that suggest the topic needs revisiting. Clearly, authors can only do this by referencing recent literature. Obviously, where older research is seminal or where aspects of the methodology rely upon it, then it is perfectly appropriate for authors to cite some older papers.

Editors say, "Is the report providing new information; is it novel or just confirmatory of well-known outcomes ?"

It's common for the introduction to end by stating the research aims. By this point you should already have a good impression of them - if the explicit aims come as a surprise, then the introduction needs improvement.

2. Materials and Methods

Academic research should be replicable, repeatable and robust - and follow best practice.

Replicable Research

This makes sufficient use of:

• Control experiments
• Repeated analyses
• Repeated experiments

These are used to make sure observed trends are not due to chance and that the same experiment could be repeated by other researchers - and result in the same outcome. Statistical analyses will not be sound if methods are not replicable. Where research is not replicable, the paper should be recommended for rejection.

Repeatable Methods

These give enough detail so that other researchers are able to carry out the same research. For example, equipment used or sampling methods should all be described in detail so that others could follow the same steps. Where methods are not detailed enough, it's usual to ask for the methods section to be revised.

Robust Research

This has enough data points to make sure the data are reliable. If there are insufficient data, it might be appropriate to recommend revision. You should also consider whether there is any in-built bias not nullified by the control experiments.

Best Practice

During these checks you should keep in mind best practice:

• Standard guidelines were followed (e.g. the CONSORT Statement for reporting randomized trials)
• The health and safety of all participants in the study was not compromised
• Ethical standards were maintained

If the research fails to reach relevant best practice standards, it's usual to recommend rejection. What's more, you don't then need to read any further.

3. Results and Discussion

This section should tell a coherent story - What happened? What was discovered or confirmed?

Certain patterns of good reporting need to be followed by the author:

• They should start by describing in simple terms what the data show
• They should make reference to statistical analyses, such as significance or goodness of fit
• Once described, they should evaluate the trends observed and explain the significance of the results to wider understanding. This can only be done by referencing published research
• The outcome should be a critical analysis of the data collected

Discussion should always, at some point, gather all the information together into a single whole. Authors should describe and discuss the overall story formed. If there are gaps or inconsistencies in the story, they should address these and suggest ways future research might confirm the findings or take the research forward.

4. Conclusions

This section is usually no more than a few paragraphs and may be presented as part of the results and discussion, or in a separate section. The conclusions should reflect upon the aims - whether they were achieved or not - and, just like the aims, should not be surprising. If the conclusions are not evidence-based, it's appropriate to ask for them to be re-written.

5. Information Gathered: Images, Graphs and Data Tables

If you find yourself looking at a piece of information from which you cannot discern a story, then you should ask for improvements in presentation. This could be an issue with titles, labels, statistical notation or image quality.

Where information is clear, you should check that:

• The results seem plausible, in case there is an error in data gathering
• The trends you can see support the paper's discussion and conclusions
• There are sufficient data. For example, in studies carried out over time are there sufficient data points to support the trends described by the author?

You should also check whether images have been edited or manipulated to emphasize the story they tell. This may be appropriate but only if authors report on how the image has been edited (e.g. by highlighting certain parts of an image). Where you feel that an image has been edited or manipulated without explanation, you should highlight this in a confidential comment to the editor in your report.

6. List of References

You will need to check referencing for accuracy, adequacy and balance.

Where a cited article is central to the author's argument, you should check the accuracy and format of the reference - and bear in mind different subject areas may use citations differently. Otherwise, it's the editor’s role to exhaustively check the reference section for accuracy and format.

You should consider if the referencing is adequate:

• Are important parts of the argument poorly supported?
• Are there published studies that show similar or dissimilar trends that should be discussed?
• If a manuscript only uses half the citations typical in its field, this may be an indicator that referencing should be improved - but don't be guided solely by quantity
• References should be relevant, recent and readily retrievable

Check for a well-balanced list of references that is:

• Helpful to the reader
• Fair to competing authors
• Not over-reliant on self-citation
• Gives due recognition to the initial discoveries and related work that led to the work under assessment

You should be able to evaluate whether the article meets the criteria for balanced referencing without looking up every reference.

7. Plagiarism

By now you will have a deep understanding of the paper's content - and you may have some concerns about plagiarism.

Identified Concern

If you find - or already knew of - a very similar paper, this may be because the author overlooked it in their own literature search. Or it may be because it is very recent or published in a journal slightly outside their usual field.

You may feel you can advise the author how to emphasize the novel aspects of their own study, so as to better differentiate it from similar research. If so, you may ask the author to discuss their aims and results, or modify their conclusions, in light of the similar article. Of course, the research similarities may be so great that they render the work unoriginal and you have no choice but to recommend rejection.

"It's very helpful when a reviewer can point out recent similar publications on the same topic by other groups, or that the authors have already published some data elsewhere ." (Editor feedback)

Suspected Concern

If you suspect plagiarism, including self-plagiarism, but cannot recall or locate exactly what is being plagiarized, notify the editor of your suspicion and ask for guidance.

Most editors have access to software that can check for plagiarism.

Editors are not out to police every paper, but when plagiarism is discovered during peer review it can be properly addressed ahead of publication. If plagiarism is discovered only after publication, the consequences are worse for both authors and readers, because a retraction may be necessary.

For detailed guidelines see COPE's Ethical guidelines for reviewers and Wiley's Best Practice Guidelines on Publishing Ethics .

8. Search Engine Optimization (SEO)

After the detailed read-through, you will be in a position to advise whether the title, abstract and key words are optimized for search purposes. In order to be effective, good SEO terms will reflect the aims of the research.

A clear title and abstract will improve the paper's search engine rankings and will influence whether the user finds and then decides to navigate to the main article. The title should contain the relevant SEO terms early on. This has a major effect on the impact of a paper, since it helps it appear in search results. A poor abstract can then lose the reader's interest and undo the benefit of an effective title - whilst the paper's abstract may appear in search results, the potential reader may go no further.

So ask yourself, while the abstract may have seemed adequate during earlier checks, does it:

• Do justice to the manuscript in this context?
• Highlight important findings sufficiently?
• Present the most interesting data?

Editors say, " Does the Abstract highlight the important findings of the study ?"

If there is a formal report format, remember to follow it. This will often comprise a range of questions followed by comment sections. Try to answer all the questions. They are there because the editor felt that they are important. If you're following an informal report format you could structure your report in three sections: summary, major issues, minor issues.

• Give positive feedback first. Authors are more likely to read your review if you do so. But don't overdo it if you will be recommending rejection
• Briefly summarize what the paper is about and what the findings are
• Try to put the findings of the paper into the context of the existing literature and current knowledge
• Indicate the significance of the work and if it is novel or mainly confirmatory
• Indicate the work's strengths, its quality and completeness
• State any major flaws or weaknesses and note any special considerations. For example, if previously held theories are being overlooked

Major Issues

• Are there any major flaws? State what they are and what the severity of their impact is on the paper
• Has similar work already been published without the authors acknowledging this?
• Are the authors presenting findings that challenge current thinking? Is the evidence they present strong enough to prove their case? Have they cited all the relevant work that would contradict their thinking and addressed it appropriately?
• If major revisions are required, try to indicate clearly what they are
• Are there any major presentational problems? Are figures & tables, language and manuscript structure all clear enough for you to accurately assess the work?
• Are there any ethical issues? If you are unsure it may be better to disclose these in the confidential comments section

Minor Issues

• Are there places where meaning is ambiguous? How can this be corrected?
• Are the correct references cited? If not, which should be cited instead/also? Are citations excessive, limited, or biased?
• Are there any factual, numerical or unit errors? If so, what are they?
• Are all tables and figures appropriate, sufficient, and correctly labelled? If not, say which are not

Your review should ultimately help the author improve their article. So be polite, honest and clear. You should also try to be objective and constructive, not subjective and destructive.

You should also:

• Write clearly and so you can be understood by people whose first language is not English
• Avoid complex or unusual words, especially ones that would even confuse native speakers
• Number your points and refer to page and line numbers in the manuscript when making specific comments
• If you have been asked to only comment on specific parts or aspects of the manuscript, you should indicate clearly which these are
• Treat the author's work the way you would like your own to be treated

Most journals give reviewers the option to provide some confidential comments to editors. Often this is where editors will want reviewers to state their recommendation - see the next section - but otherwise this area is best reserved for communicating malpractice such as suspected plagiarism, fraud, unattributed work, unethical procedures, duplicate publication, bias or other conflicts of interest.

However, this doesn't give reviewers permission to 'backstab' the author. Authors can't see this feedback and are unable to give their side of the story unless the editor asks them to. So in the spirit of fairness, write comments to editors as though authors might read them too.

Reviewers should check the preferences of individual journals as to where they want review decisions to be stated. In particular, bear in mind that some journals will not want the recommendation included in any comments to authors, as this can cause editors difficulty later - see Section 11 for more advice about working with editors.

You will normally be asked to indicate your recommendation (e.g. accept, reject, revise and resubmit, etc.) from a fixed-choice list and then to enter your comments into a separate text box.

Recommending Acceptance

If you're recommending acceptance, give details outlining why, and if there are any areas that could be improved. Don't just give a short, cursory remark such as 'great, accept'. See Improving the Manuscript

Recommending Revision

Where improvements are needed, a recommendation for major or minor revision is typical. You may also choose to state whether you opt in or out of the post-revision review too. If recommending revision, state specific changes you feel need to be made. The author can then reply to each point in turn.

Some journals offer the option to recommend rejection with the possibility of resubmission – this is most relevant where substantial, major revision is necessary.

What can reviewers do to help? " Be clear in their comments to the author (or editor) which points are absolutely critical if the paper is given an opportunity for revisio n." (Jonathon Halbesleben, Editor of Journal of Occupational and Organizational Psychology)

Recommending Rejection

If recommending rejection or major revision, state this clearly in your review (and see the next section, 'When recommending rejection').

Where manuscripts have serious flaws you should not spend any time polishing the review you've drafted or give detailed advice on presentation.

Editors say, " If a reviewer suggests a rejection, but her/his comments are not detailed or helpful, it does not help the editor in making a decision ."

In your recommendations for the author, you should:

• Give constructive feedback describing ways that they could improve the research
• Keep the focus on the research and not the author. This is an extremely important part of your job as a reviewer
• Avoid making critical confidential comments to the editor while being polite and encouraging to the author - the latter may not understand why their manuscript has been rejected. Also, they won't get feedback on how to improve their research and it could trigger an appeal

Remember to give constructive criticism even if recommending rejection. This helps developing researchers improve their work and explains to the editor why you felt the manuscript should not be published.

" When the comments seem really positive, but the recommendation is rejection…it puts the editor in a tough position of having to reject a paper when the comments make it sound like a great paper ." (Jonathon Halbesleben, Editor of Journal of Occupational and Organizational Psychology)

Visit our Wiley Author Learning and Training Channel for expert advice on peer review.

Watch the video, Ethical considerations of Peer Review

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Organizing Your Social Sciences Research Paper

• 5. The Literature Review
• Purpose of Guide
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• Glossary of Research Terms
• Reading Research Effectively
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A literature review surveys prior research published in books, scholarly articles, and any other sources relevant to a particular issue, area of research, or theory, and by so doing, provides a description, summary, and critical evaluation of these works in relation to the research problem being investigated. Literature reviews are designed to provide an overview of sources you have used in researching a particular topic and to demonstrate to your readers how your research fits within existing scholarship about the topic.

Fink, Arlene. Conducting Research Literature Reviews: From the Internet to Paper . Fourth edition. Thousand Oaks, CA: SAGE, 2014.

Importance of a Good Literature Review

A literature review may consist of simply a summary of key sources, but in the social sciences, a literature review usually has an organizational pattern and combines both summary and synthesis, often within specific conceptual categories . A summary is a recap of the important information of the source, but a synthesis is a re-organization, or a reshuffling, of that information in a way that informs how you are planning to investigate a research problem. The analytical features of a literature review might:

• Give a new interpretation of old material or combine new with old interpretations,
• Trace the intellectual progression of the field, including major debates,
• Depending on the situation, evaluate the sources and advise the reader on the most pertinent or relevant research, or
• Usually in the conclusion of a literature review, identify where gaps exist in how a problem has been researched to date.

Given this, the purpose of a literature review is to:

• Place each work in the context of its contribution to understanding the research problem being studied.
• Describe the relationship of each work to the others under consideration.
• Identify new ways to interpret prior research.
• Reveal any gaps that exist in the literature.
• Resolve conflicts amongst seemingly contradictory previous studies.
• Identify areas of prior scholarship to prevent duplication of effort.
• Point the way in fulfilling a need for additional research.
• Locate your own research within the context of existing literature [very important].

Fink, Arlene. Conducting Research Literature Reviews: From the Internet to Paper. 2nd ed. Thousand Oaks, CA: Sage, 2005; Hart, Chris. Doing a Literature Review: Releasing the Social Science Research Imagination . Thousand Oaks, CA: Sage Publications, 1998; Jesson, Jill. Doing Your Literature Review: Traditional and Systematic Techniques . Los Angeles, CA: SAGE, 2011; Knopf, Jeffrey W. "Doing a Literature Review." PS: Political Science and Politics 39 (January 2006): 127-132; Ridley, Diana. The Literature Review: A Step-by-Step Guide for Students . 2nd ed. Los Angeles, CA: SAGE, 2012.

Types of Literature Reviews

It is important to think of knowledge in a given field as consisting of three layers. First, there are the primary studies that researchers conduct and publish. Second are the reviews of those studies that summarize and offer new interpretations built from and often extending beyond the primary studies. Third, there are the perceptions, conclusions, opinion, and interpretations that are shared informally among scholars that become part of the body of epistemological traditions within the field.

In composing a literature review, it is important to note that it is often this third layer of knowledge that is cited as "true" even though it often has only a loose relationship to the primary studies and secondary literature reviews. Given this, while literature reviews are designed to provide an overview and synthesis of pertinent sources you have explored, there are a number of approaches you could adopt depending upon the type of analysis underpinning your study.

Argumentative Review This form examines literature selectively in order to support or refute an argument, deeply embedded assumption, or philosophical problem already established in the literature. The purpose is to develop a body of literature that establishes a contrarian viewpoint. Given the value-laden nature of some social science research [e.g., educational reform; immigration control], argumentative approaches to analyzing the literature can be a legitimate and important form of discourse. However, note that they can also introduce problems of bias when they are used to make summary claims of the sort found in systematic reviews [see below].

Integrative Review Considered a form of research that reviews, critiques, and synthesizes representative literature on a topic in an integrated way such that new frameworks and perspectives on the topic are generated. The body of literature includes all studies that address related or identical hypotheses or research problems. A well-done integrative review meets the same standards as primary research in regard to clarity, rigor, and replication. This is the most common form of review in the social sciences.

Historical Review Few things rest in isolation from historical precedent. Historical literature reviews focus on examining research throughout a period of time, often starting with the first time an issue, concept, theory, phenomena emerged in the literature, then tracing its evolution within the scholarship of a discipline. The purpose is to place research in a historical context to show familiarity with state-of-the-art developments and to identify the likely directions for future research.

Methodological Review A review does not always focus on what someone said [findings], but how they came about saying what they say [method of analysis]. Reviewing methods of analysis provides a framework of understanding at different levels [i.e. those of theory, substantive fields, research approaches, and data collection and analysis techniques], how researchers draw upon a wide variety of knowledge ranging from the conceptual level to practical documents for use in fieldwork in the areas of ontological and epistemological consideration, quantitative and qualitative integration, sampling, interviewing, data collection, and data analysis. This approach helps highlight ethical issues which you should be aware of and consider as you go through your own study.

Systematic Review This form consists of an overview of existing evidence pertinent to a clearly formulated research question, which uses pre-specified and standardized methods to identify and critically appraise relevant research, and to collect, report, and analyze data from the studies that are included in the review. The goal is to deliberately document, critically evaluate, and summarize scientifically all of the research about a clearly defined research problem . Typically it focuses on a very specific empirical question, often posed in a cause-and-effect form, such as "To what extent does A contribute to B?" This type of literature review is primarily applied to examining prior research studies in clinical medicine and allied health fields, but it is increasingly being used in the social sciences.

Theoretical Review The purpose of this form is to examine the corpus of theory that has accumulated in regard to an issue, concept, theory, phenomena. The theoretical literature review helps to establish what theories already exist, the relationships between them, to what degree the existing theories have been investigated, and to develop new hypotheses to be tested. Often this form is used to help establish a lack of appropriate theories or reveal that current theories are inadequate for explaining new or emerging research problems. The unit of analysis can focus on a theoretical concept or a whole theory or framework.

NOTE: Most often the literature review will incorporate some combination of types. For example, a review that examines literature supporting or refuting an argument, assumption, or philosophical problem related to the research problem will also need to include writing supported by sources that establish the history of these arguments in the literature.

Baumeister, Roy F. and Mark R. Leary. "Writing Narrative Literature Reviews."  Review of General Psychology 1 (September 1997): 311-320; Mark R. Fink, Arlene. Conducting Research Literature Reviews: From the Internet to Paper . 2nd ed. Thousand Oaks, CA: Sage, 2005; Hart, Chris. Doing a Literature Review: Releasing the Social Science Research Imagination . Thousand Oaks, CA: Sage Publications, 1998; Kennedy, Mary M. "Defining a Literature." Educational Researcher 36 (April 2007): 139-147; Petticrew, Mark and Helen Roberts. Systematic Reviews in the Social Sciences: A Practical Guide . Malden, MA: Blackwell Publishers, 2006; Torracro, Richard. "Writing Integrative Literature Reviews: Guidelines and Examples." Human Resource Development Review 4 (September 2005): 356-367; Rocco, Tonette S. and Maria S. Plakhotnik. "Literature Reviews, Conceptual Frameworks, and Theoretical Frameworks: Terms, Functions, and Distinctions." Human Ressource Development Review 8 (March 2008): 120-130; Sutton, Anthea. Systematic Approaches to a Successful Literature Review . Los Angeles, CA: Sage Publications, 2016.

Structure and Writing Style

I.  Thinking About Your Literature Review

The structure of a literature review should include the following in support of understanding the research problem :

• An overview of the subject, issue, or theory under consideration, along with the objectives of the literature review,
• Division of works under review into themes or categories [e.g. works that support a particular position, those against, and those offering alternative approaches entirely],
• An explanation of how each work is similar to and how it varies from the others,
• Conclusions as to which pieces are best considered in their argument, are most convincing of their opinions, and make the greatest contribution to the understanding and development of their area of research.

The critical evaluation of each work should consider :

• Provenance -- what are the author's credentials? Are the author's arguments supported by evidence [e.g. primary historical material, case studies, narratives, statistics, recent scientific findings]?
• Methodology -- were the techniques used to identify, gather, and analyze the data appropriate to addressing the research problem? Was the sample size appropriate? Were the results effectively interpreted and reported?
• Objectivity -- is the author's perspective even-handed or prejudicial? Is contrary data considered or is certain pertinent information ignored to prove the author's point?
• Persuasiveness -- which of the author's theses are most convincing or least convincing?
• Validity -- are the author's arguments and conclusions convincing? Does the work ultimately contribute in any significant way to an understanding of the subject?

II.  Development of the Literature Review

Four Basic Stages of Writing 1.  Problem formulation -- which topic or field is being examined and what are its component issues? 2.  Literature search -- finding materials relevant to the subject being explored. 3.  Data evaluation -- determining which literature makes a significant contribution to the understanding of the topic. 4.  Analysis and interpretation -- discussing the findings and conclusions of pertinent literature.

Consider the following issues before writing the literature review: Clarify If your assignment is not specific about what form your literature review should take, seek clarification from your professor by asking these questions: 1.  Roughly how many sources would be appropriate to include? 2.  What types of sources should I review (books, journal articles, websites; scholarly versus popular sources)? 3.  Should I summarize, synthesize, or critique sources by discussing a common theme or issue? 4.  Should I evaluate the sources in any way beyond evaluating how they relate to understanding the research problem? 5.  Should I provide subheadings and other background information, such as definitions and/or a history? Find Models Use the exercise of reviewing the literature to examine how authors in your discipline or area of interest have composed their literature review sections. Read them to get a sense of the types of themes you might want to look for in your own research or to identify ways to organize your final review. The bibliography or reference section of sources you've already read, such as required readings in the course syllabus, are also excellent entry points into your own research. Narrow the Topic The narrower your topic, the easier it will be to limit the number of sources you need to read in order to obtain a good survey of relevant resources. Your professor will probably not expect you to read everything that's available about the topic, but you'll make the act of reviewing easier if you first limit scope of the research problem. A good strategy is to begin by searching the USC Libraries Catalog for recent books about the topic and review the table of contents for chapters that focuses on specific issues. You can also review the indexes of books to find references to specific issues that can serve as the focus of your research. For example, a book surveying the history of the Israeli-Palestinian conflict may include a chapter on the role Egypt has played in mediating the conflict, or look in the index for the pages where Egypt is mentioned in the text. Consider Whether Your Sources are Current Some disciplines require that you use information that is as current as possible. This is particularly true in disciplines in medicine and the sciences where research conducted becomes obsolete very quickly as new discoveries are made. However, when writing a review in the social sciences, a survey of the history of the literature may be required. In other words, a complete understanding the research problem requires you to deliberately examine how knowledge and perspectives have changed over time. Sort through other current bibliographies or literature reviews in the field to get a sense of what your discipline expects. You can also use this method to explore what is considered by scholars to be a "hot topic" and what is not.

III.  Ways to Organize Your Literature Review

Chronology of Events If your review follows the chronological method, you could write about the materials according to when they were published. This approach should only be followed if a clear path of research building on previous research can be identified and that these trends follow a clear chronological order of development. For example, a literature review that focuses on continuing research about the emergence of German economic power after the fall of the Soviet Union. By Publication Order your sources by publication chronology, then, only if the order demonstrates a more important trend. For instance, you could order a review of literature on environmental studies of brown fields if the progression revealed, for example, a change in the soil collection practices of the researchers who wrote and/or conducted the studies. Thematic [“conceptual categories”] A thematic literature review is the most common approach to summarizing prior research in the social and behavioral sciences. Thematic reviews are organized around a topic or issue, rather than the progression of time, although the progression of time may still be incorporated into a thematic review. For example, a review of the Internet’s impact on American presidential politics could focus on the development of online political satire. While the study focuses on one topic, the Internet’s impact on American presidential politics, it would still be organized chronologically reflecting technological developments in media. The difference in this example between a "chronological" and a "thematic" approach is what is emphasized the most: themes related to the role of the Internet in presidential politics. Note that more authentic thematic reviews tend to break away from chronological order. A review organized in this manner would shift between time periods within each section according to the point being made. Methodological A methodological approach focuses on the methods utilized by the researcher. For the Internet in American presidential politics project, one methodological approach would be to look at cultural differences between the portrayal of American presidents on American, British, and French websites. Or the review might focus on the fundraising impact of the Internet on a particular political party. A methodological scope will influence either the types of documents in the review or the way in which these documents are discussed.

Other Sections of Your Literature Review Once you've decided on the organizational method for your literature review, the sections you need to include in the paper should be easy to figure out because they arise from your organizational strategy. In other words, a chronological review would have subsections for each vital time period; a thematic review would have subtopics based upon factors that relate to the theme or issue. However, sometimes you may need to add additional sections that are necessary for your study, but do not fit in the organizational strategy of the body. What other sections you include in the body is up to you. However, only include what is necessary for the reader to locate your study within the larger scholarship about the research problem.

Here are examples of other sections, usually in the form of a single paragraph, you may need to include depending on the type of review you write:

• Current Situation : Information necessary to understand the current topic or focus of the literature review.
• Sources Used : Describes the methods and resources [e.g., databases] you used to identify the literature you reviewed.
• History : The chronological progression of the field, the research literature, or an idea that is necessary to understand the literature review, if the body of the literature review is not already a chronology.
• Selection Methods : Criteria you used to select (and perhaps exclude) sources in your literature review. For instance, you might explain that your review includes only peer-reviewed [i.e., scholarly] sources.
• Standards : Description of the way in which you present your information.
• Questions for Further Research : What questions about the field has the review sparked? How will you further your research as a result of the review?

IV.  Writing Your Literature Review

Once you've settled on how to organize your literature review, you're ready to write each section. When writing your review, keep in mind these issues.

Use Evidence A literature review section is, in this sense, just like any other academic research paper. Your interpretation of the available sources must be backed up with evidence [citations] that demonstrates that what you are saying is valid. Be Selective Select only the most important points in each source to highlight in the review. The type of information you choose to mention should relate directly to the research problem, whether it is thematic, methodological, or chronological. Related items that provide additional information, but that are not key to understanding the research problem, can be included in a list of further readings . Use Quotes Sparingly Some short quotes are appropriate if you want to emphasize a point, or if what an author stated cannot be easily paraphrased. Sometimes you may need to quote certain terminology that was coined by the author, is not common knowledge, or taken directly from the study. Do not use extensive quotes as a substitute for using your own words in reviewing the literature. Summarize and Synthesize Remember to summarize and synthesize your sources within each thematic paragraph as well as throughout the review. Recapitulate important features of a research study, but then synthesize it by rephrasing the study's significance and relating it to your own work and the work of others. Keep Your Own Voice While the literature review presents others' ideas, your voice [the writer's] should remain front and center. For example, weave references to other sources into what you are writing but maintain your own voice by starting and ending the paragraph with your own ideas and wording. Use Caution When Paraphrasing When paraphrasing a source that is not your own, be sure to represent the author's information or opinions accurately and in your own words. Even when paraphrasing an author’s work, you still must provide a citation to that work.

V.  Common Mistakes to Avoid

These are the most common mistakes made in reviewing social science research literature.

• Sources in your literature review do not clearly relate to the research problem;
• You do not take sufficient time to define and identify the most relevant sources to use in the literature review related to the research problem;
• Relies exclusively on secondary analytical sources rather than including relevant primary research studies or data;
• Uncritically accepts another researcher's findings and interpretations as valid, rather than examining critically all aspects of the research design and analysis;
• Does not describe the search procedures that were used in identifying the literature to review;
• Reports isolated statistical results rather than synthesizing them in chi-squared or meta-analytic methods; and,
• Only includes research that validates assumptions and does not consider contrary findings and alternative interpretations found in the literature.

Cook, Kathleen E. and Elise Murowchick. “Do Literature Review Skills Transfer from One Course to Another?” Psychology Learning and Teaching 13 (March 2014): 3-11; Fink, Arlene. Conducting Research Literature Reviews: From the Internet to Paper . 2nd ed. Thousand Oaks, CA: Sage, 2005; Hart, Chris. Doing a Literature Review: Releasing the Social Science Research Imagination . Thousand Oaks, CA: Sage Publications, 1998; Jesson, Jill. Doing Your Literature Review: Traditional and Systematic Techniques . London: SAGE, 2011; Literature Review Handout. Online Writing Center. Liberty University; Literature Reviews. The Writing Center. University of North Carolina; Onwuegbuzie, Anthony J. and Rebecca Frels. Seven Steps to a Comprehensive Literature Review: A Multimodal and Cultural Approach . Los Angeles, CA: SAGE, 2016; Ridley, Diana. The Literature Review: A Step-by-Step Guide for Students . 2nd ed. Los Angeles, CA: SAGE, 2012; Randolph, Justus J. “A Guide to Writing the Dissertation Literature Review." Practical Assessment, Research, and Evaluation. vol. 14, June 2009; Sutton, Anthea. Systematic Approaches to a Successful Literature Review . Los Angeles, CA: Sage Publications, 2016; Taylor, Dena. The Literature Review: A Few Tips On Conducting It. University College Writing Centre. University of Toronto; Writing a Literature Review. Academic Skills Centre. University of Canberra.

Writing Tip

Break Out of Your Disciplinary Box!

Thinking interdisciplinarily about a research problem can be a rewarding exercise in applying new ideas, theories, or concepts to an old problem. For example, what might cultural anthropologists say about the continuing conflict in the Middle East? In what ways might geographers view the need for better distribution of social service agencies in large cities than how social workers might study the issue? You don’t want to substitute a thorough review of core research literature in your discipline for studies conducted in other fields of study. However, particularly in the social sciences, thinking about research problems from multiple vectors is a key strategy for finding new solutions to a problem or gaining a new perspective. Consult with a librarian about identifying research databases in other disciplines; almost every field of study has at least one comprehensive database devoted to indexing its research literature.

Frodeman, Robert. The Oxford Handbook of Interdisciplinarity . New York: Oxford University Press, 2010.

Another Writing Tip

Don't Just Review for Content!

While conducting a review of the literature, maximize the time you devote to writing this part of your paper by thinking broadly about what you should be looking for and evaluating. Review not just what scholars are saying, but how are they saying it. Some questions to ask:

• How are they organizing their ideas?
• What methods have they used to study the problem?
• What theories have been used to explain, predict, or understand their research problem?
• What sources have they cited to support their conclusions?
• How have they used non-textual elements [e.g., charts, graphs, figures, etc.] to illustrate key points?

When you begin to write your literature review section, you'll be glad you dug deeper into how the research was designed and constructed because it establishes a means for developing more substantial analysis and interpretation of the research problem.

Hart, Chris. Doing a Literature Review: Releasing the Social Science Research Imagination . Thousand Oaks, CA: Sage Publications, 1 998.

Yet Another Writing Tip

When Do I Know I Can Stop Looking and Move On?

Here are several strategies you can utilize to assess whether you've thoroughly reviewed the literature:

• Look for repeating patterns in the research findings . If the same thing is being said, just by different people, then this likely demonstrates that the research problem has hit a conceptual dead end. At this point consider: Does your study extend current research?  Does it forge a new path? Or, does is merely add more of the same thing being said?
• Look at sources the authors cite to in their work . If you begin to see the same researchers cited again and again, then this is often an indication that no new ideas have been generated to address the research problem.
• Search Google Scholar to identify who has subsequently cited leading scholars already identified in your literature review [see next sub-tab]. This is called citation tracking and there are a number of sources that can help you identify who has cited whom, particularly scholars from outside of your discipline. Here again, if the same authors are being cited again and again, this may indicate no new literature has been written on the topic.

Onwuegbuzie, Anthony J. and Rebecca Frels. Seven Steps to a Comprehensive Literature Review: A Multimodal and Cultural Approach . Los Angeles, CA: Sage, 2016; Sutton, Anthea. Systematic Approaches to a Successful Literature Review . Los Angeles, CA: Sage Publications, 2016.

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Infographic: 5 Differences between a research paper and a review paper

Andrea Hayward

There are different types of scholarly literature . Some of these require researchers to conduct an original study, whereas others can be based on previously published research. Understanding each of these types and also how they differ from one another can be rather confusing for researchers, especially early career researchers. One of the most popular questions on our Q&A forum - What is the difference between a research paper and a review paper? - led us to conclude that of all the types of scholarly literature, researchers tend to be most perplexed by the distinction between a research paper and a review paper. This infographic explains the five main differences between these two types of scholarly papers. 

Feel free to download a PDF version of this infographic and print it out as handy reference.

You might find this course helpful: Manuscript writing

Related reading:

To learn about the different types of review papers, browse through this SlideShare presentation -  What types of articles do journals publish?

References:

• What is the difference between a research paper and a review paper?
• 6 Article types that journals publish: A guide for early career researchers
• Review vs. Research Articles
• Frontiers in Neuroscience - Article types

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Systematic review and meta-analysis of hepatitis E seroprevalence in Southeast Asia: a comprehensive assessment of epidemiological patterns

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The burden of hepatitis E in Southeast Asia is substantial, influenced by its distinct socio-economic and environmental factors, as well as variations in healthcare systems. The aim of this study was to assess the pooled seroprevalence of hepatitis E across countries within the Southeast Asian region by the UN division.

The study analyzed 66 papers across PubMed, Web of Science, and Scopus databases, encompassing data from of 44,850 individuals focusing on anti-HEV seroprevalence. The investigation spanned nine countries, excluding Brunei and East Timor due to lack of data. The pooled prevalence of anti-HEV IgG was determined to be 21.03%, with the highest prevalence observed in Myanmar (33.46%) and the lowest in Malaysia (5.93%). IgM prevalence was highest in Indonesia (12.43%) and lowest in Malaysia (0.91%). The study stratified populations into high-risk (farm workers, chronic patients) and low-risk groups (general population, blood donors, pregnant women, hospital patients). It revealed a higher IgG—28.9%, IgM—4.42% prevalence in the former group, while the latter group exhibited figures of 17.86% and 3.15%, respectively, indicating occupational and health-related vulnerabilities to HEV.

A temporal analysis (1987–2023), indicated an upward trend in both IgG and IgM prevalence, suggesting an escalating HEV burden.

These findings contribute to a better understanding of HEV seroprevalence in Southeast Asia, shedding light on important public health implications and suggesting directions for further research and intervention strategies.

Research Question

Investigate the seroprevalence of hepatitis E virus (HEV) in Southeast Asian countries focusing on different patterns, timelines, and population cohorts.

Sporadic Transmission of IgG and IgM Prevalence:

• Pooled anti-HEV IgG prevalence: 21.03%

• Pooled anti-HEV IgM prevalence: 3.49%

Seroprevalence among specific groups:

High-risk group (farm workers and chronic patients):

• anti-HEV IgG: 28.9%

• anti-HEV IgM: 4.42%

Low-risk group (general population, blood donors, pregnant women, hospital patients):

• anti-HEV IgG: 17.86%

• anti-HEV IgM: 3.15%

Temporal Seroprevalence of HEV:

Anti-HEV IgG prevalence increased over decades (1987–1999; 2000–2010; 2011–2023): 12.47%, 18.43%, 29.17% as an anti-HEV IgM prevalence: 1.92%, 2.44%, 5.27%

Provides a comprehensive overview of HEV seroprevalence in Southeast Asia.

Highlights variation in seroprevalence among different population groups.

Reveals increasing trend in HEV seroprevalence over the years.

Distinguishes between sporadic and epidemic cases for a better understanding of transmission dynamics.

Peer Review reports

Introduction

Hepatitis E is a major global health concern caused by the hepatitis E virus (HEV), which is a small, nonenveloped, single-stranded, positive-sense RNA virus belonging to the Paslahepevirus genus in the Hepeviridae family. There are eight genotypes of HEV: HEV-1 and HEV-2 infect only humans, HEV-3, HEV-4, and HEV-7 infect both humans and animals, while HEV-5, HEV-6, and HEV-8 infect only animals [ 1 ].

HEV infections affect millions of people worldwide each year, resulting in a significant number of symptomatic cases and deaths. In 2015, the World Health Organization (WHO) reported approximately 44,000 deaths from hepatitis E, accounting for 3.3% of overall mortality attributed to viral hepatitis [ 2 ]. The primary mode of transmission for hepatitis E is through the fecal–oral route. Outbreaks of the disease are often associated with heavy rainfall and flooding [ 3 , 4 ]. Additionally, sporadic cases can occur due to poor sanitation, vertical transmission, blood transfusion or close contact with infected animals, which serve as hosts for the virus [ 5 ]. Southeast Asia carries a substantial burden of hepatitis E, influenced by its unique socio-economic and environmental factors as well as variations in healthcare systems. Understanding the seroprevalence of hepatitis E in this region is crucial for implementing targeted public health interventions and allocating resources. To achieve the effective control and prevention of HEV, it is required to address the waterborne transmission and considering the specific characteristics of each region. By taking these measures, healthcare authorities can work towards reducing the global impact of hepatitis E on public health. Systematic reviews and meta-analyses on hepatitis E play a crucial role in synthesizing and integrating existing research findings, providing comprehensive insights into the epidemiology, transmission, and burden of the disease, thereby aiding evidence-based decision-making and public health strategies [ 6 , 7 ].

Recent systematic reviews and meta-analysis conducted on hepatitis E have varied in their scope or were limited by a smaller number of source materials [ 8 , 9 ]. The objective of this study was to determine the pooled seroprevalence of hepatitis E in countries within Southeast Asia by aggregating findings from a multitude of primary studies conducted across the region.

To commence this systematic review and meta-analysis, we adhered to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines and used the PRISMA assessment checklist [Supplementary Table  1 ]. The study included pertinent research conducted within the population of Southeast Asian countries, as outlined by the United Nations [ 10 ], and perform a meta-analysis on the seroprevalence of hepatitis E in this specific region.

PICOT assessment

In this systematic review and meta-analysis, the eligible population comprised individuals from the Southeast Asia region, irrespective of age, gender, ethnic characteristics, or specific chronic diseases. However, studies involving populations outside the designated countries, travelers, migrants, animal species studies, and those lacking clear descriptions of the study population were excluded.

Intervention and comparison

Intervention and comparison are not applicable to the prevalence studies.

Anti-HEV antibodies positivity either total antibodies or IgG or IgM among the Southeast Asian countries' population was assessed.

All studies conducted between 1987 and 2023 were included in this meta-analysis.

Search strategy

To conduct the data search, we utilized three databases, namely “PubMed”, “Scopus”, and “Web of Science”. The search terms comprised keywords related to the Hepatitis E virus, such as “Hepatitis E virus” OR “Hepatitis E” OR “HEV” AND names of each country “Brunei”, “Cambodia”, “Timor-Leste” OR “East-Timor”, “Laos” OR “Lao PDR”, “Indonesia”, “Malaysia”, “Myanmar” OR “Burma”, “Philippines”, “Singapore”, “Thailand”, “Vietnam” and “Southeast Asia”.

The search process in the databases finished on May 29 th , 2023, with two members of the study team conducting independent searches. Subsequently, the search results were unified. A grey literature search was performed from June 25 th to 30 th , 2023, by examining the references of review manuscripts and conference materials, along with using specific keywords in the Google Scholar database. Notably, during the gray literature search, additional studies from the Philippines that were initially missing in the first search were identified and included. Moreover, due to the diverse language expertise of the team, studies in Russian and French related to Cambodia and Vietnam were also considered for inclusion.

After applying the inclusion and exclusion criteria, each article selected for this systematic review (SR) was considered relevant. The quality assessment of each article was conducted using specific JBI critical appraisal instruments [ 11 ] [Supplementary Table  2 ].

Sporadic transmission of HEV infection

For the systematic review and meta-analysis of sporadic infection of HEV, we divided the study population into cohorts by countries, by risk of acquiring HEV—low and high risk. The low risk cohort included the general population (apparently healthy individuals, students, some ethnic populations, or individuals included in original studies as “general population”), blood donors, pregnant women, and hospital patients, while pig farmers, those with chronic hepatitis, HIV positive patients, and solid organ transplant patients in the high-risk group.

Lastly, we analyzed data in three decades—1987–1999, 2000–2010, and 2011–2023—to reveal seroprevalence rates over time.

Epidemic outbreaks of HEV infection

We separated epidemic outbreaks from sporadic cases due to distinct patterns and scale of transmission in epidemy. Epidemics are characterized by rapid and widespread transmission, affecting a large population within a short period and often following a specific pattern or route of propagation.

Statistical analysis

A meta-analysis of proportions was conducted using the 'meta' and 'metafor' packages in the R statistical software. To account for small proportions, the Freeman-Tukey double arcsine method was applied to transform the data. The Dersimonian and Laird method, which employs a random-effects model, was utilized for the meta-analysis, and the results were presented in a forest plot. Confidence intervals (CIs) for the proportions of individual studies were computed using the Clopper-Pearson method.

Heterogeneity was evaluated using the Cochran Q test and quantified by the I 2 index. Heterogeneity was considered significant if the p -value of the Cochran Q test was below 0.05.

For the assessment of publication bias, a funnel plot displaying the transformed proportions against the sample size was created. The symmetry of the plot was examined using the Egger test ( p  < 0.1).

The initial search yielded 1641 articles, which covered 9 out of 11 Southeast Asia countries. We couldn't find any information on hepatitis E from Brunei. We excluded a study from East Timor because it focused on the wrong population (US Army troops). The final screening resulted in the selection of 57 relevant studies, and the grey literature search added 9 more papers that met our inclusion criteria (Fig.  1 ). Among 9 papers through a grey literature, two relevant studies from the Philippines [ 12 , 13 ], one each from Indonesia [ 14 ] and Lao PDR [ 15 ], one study covered both Vietnam and Cambodia [ 16 ], one study provided HEV seroepidemiology information for Myanmar, Thailand, and Vietnam [ 17 ], two studies reported in Russian [ 18 , 19 ] (from Vietnam) and one reported in French [ 16 ] (from Vietnam and Cambodia). In total, our analysis included 66 papers from which we extracted data. This involved a total of 44,850 individuals (Table  1 ).

Flowchart of the identification, inclusion, and exclusion of the study. Table under flowchart informing about the studies which were found by the initial search in databases

Sporadic transmission IgG and IgM prevalence in Southeast Asian countries (excluding outbreak settings)

The sporadic cases involving 42,248 participants out of 44,850 participants (the remaining 2,602 people are considered in the “ Epidemic outbreaks ” section) from Southeast Asian countries the pooled prevalence of IgG was found to be 21.03%, while for IgM, it was 3.49% among 34,480 individuals who were tested (Fig. 2 ). Among these countries, Myanmar registered the highest pooled prevalence of IgG at 33.46%, while Malaysia had the lowest at 5.93%. For IgM prevalence, Indonesia had the highest rate at 12.43%, and Malaysia again had the lowest at 0.91% (Table  2 ) [Supplementary Figures  1 and 6 ].

Forest plot of meta-analysis of the prevalence of anti-HEV IgG ( A ) and anti-HEV IgM ( B ) in Southeast Asian countries. The plot includes the number of study participants for each country

Seroprevalence among specific groups

High risk of acquiring hev.

The high-risk group, which included farm workers and chronic patients, demonstrated a pooled anti-HEV IgG prevalence of 28.9%, with IgM prevalence at 4.42% [Supplementary Figures  2 and 8 ].

Chronic patients

This group, comprising individuals with chronic liver disease, HIV infection, or solid organ transplantation, exhibited the highest prevalence of pooled IgG among all cohorts, standing at 29.2%. Additionally, IgM prevalence was 3.9% [Supplementary Figures  2 and 7 ].

Farm workers

Farm workers were divided into several subgroups based on exposure to animals (reservoirs of HEV), including pig or ruminant farmers, slaughterhouse workers, butchers, and meat retailers. Among this group, the highest IgG prevalence was observed at 28.4%, while the pooled IgM level was 6.21% [Supplementary Figures  2 and 7 ].

Low risk of acquiring HEV

The low-risk group, comprising the general population, blood donors, pregnant women, and hospital patients, exhibited anti-HEV IgG and IgM prevalence of 17.86% and 3.15%, respectively. [Supplementary Figures  2 and 9 ].

General population

The general population in Southeast Asian countries, represented by 22,571 individuals, showed a presence of IgG in 21.4% of them. IgM was tested in 10,304 participants, and 2.63% of acute infection cases were identified [Supplementary Figures  2 and 7 ].

Blood donors

Blood donors, as a selected subgroup of the general population, exhibit differences in health status, age, gender distribution, and representativeness, warranting separate assessment. Among blood donors in Southeast Asian countries, the pooled prevalence of IgG and IgM were found to be 11.77% and 0.83%, respectively [Supplementary Figures  2 and 7 ].

Pregnant women

Pregnant women considered a vulnerable group regarding disease consequences, demonstrated an anti-HEV IgG prevalence of 18.56% among 1,670 individuals included in the study. Furthermore, 1.54% of them tested positive for anti-HEV IgM [Supplementary Figures  2 and 7 ].

Hospital patients

A group of 18,792 patients who visited hospitals with clinical signs of acute infection, jaundice, high temperature, and elevated liver enzymes, showed anti-HEV IgG and IgM prevalence of 16.3% and 4.45%, respectively [Supplementary Figures  2 and 7 ].

Temporal seroprevalence of HEV

Given the studies' long duration, the data was presented by decades: 1987–1999, 2000–2010, and 2011–2023. The prevalence of IgG showed an upward trend over these decades, with rates of 12.47%, 18.43%, and 29.17%. Similarly, for IgM, the prevalence rates were 1.92%, 2.44%, and 5.27% for the first, second, and third decades, respectively (Fig. 3 ).

The prevalence of anti-HEV IgG and IgM in Southeast Asian countries throughout the decades

Evaluating the trend of seroprevalence over decades within the same population and country proved challenging due to the limited availability of research papers. Consequently, we assessed anti-HEV antibody prevalence over decades, considering population cohorts and individual countries.

In Fig.  4 , we can see that all population groups show a consistent increase in the prevalence of both IgG and IgM antibodies over the decades. Figure  5 , we analyze the prevalence of anti-HEV antibodies in different countries over time, except for Indonesia and Malaysia, where we observe an increase in prevalence.

The epidemiological data regarding the occurrence of anti-HEV IgG ( A ) and anti-HEV IgM ( B ) antibodies within population cohorts across Southeast Asian nations divided by decades. The population cohorts delineated by the disrupted lines in the figure lack comprehensive data representation, as they provide information for only two out of three decades. Blood donors group has the anti-HEV IgM only for the last decade

The epidemiological data regarding the occurrence of anti-HEV IgG ( A ) and anti-HEV IgM ( B ) antibodies within countries of Southeast Asia divided by decades. The countries delineated by the disrupted lines in the figure lack comprehensive data representation, as they provide information for only two out of three decades. Philippines has the anti-HEV IgG antibodies information only for the first decade. Philippines, Myanmar, Singapore have anti-HEV IgM information only for single decade

Some studies lacked information on the collection time of the samples [ 13 , 19 , 41 , 48 , 59 , 62 , 64 , 82 ]. In these studies, the pooled IgG and IgM prevalence was 26.5% and 4.75%, respectively [Supplementary Figures  3 , 4 , 5 , 10 , 11 , 12 ].

Epidemic outbreaks

We separated epidemic outbreaks from sporadic cases due to distinct patterns and scale of transmission in epidemy. Epidemics are characterized by rapid and widespread transmission, affecting a large population within a short period and often following a specific pattern or route of propagation. The outbreaks occurred between 1987 and 1998 in several Southeast Asian countries, namely Indonesia [ 31 , 33 , 34 ], Vietnam [ 77 ], and Myanmar [ 54 ] [Supplementary Figure  13 ]. These outbreak investigations involved a total of 2,602 individuals, with most participants from Indonesia (2,292 individuals). The studies were mainly conducted using a case–control design. Among the participants, 876 were considered controls, while 1,726 were classified as cases. The pooled prevalence of total anti-HEV immunoglobulins was estimated as 61.6% (95% CI 57.1–66) (Table  2 ).

Assessment of publication bias

We checked for publication bias using a funnel plot and Egger's test. Both the studies on anti-HEV IgG and IgM showed asymmetry with Egger's test indicating a p -value less than 0.001 for both cases (Fig. 6 ).

Funnel plot of anti-HEV IgG ( A ) and anti-HEV IgM prevalence. Double arcsine transformed proportion of individual studies is plotted against the sample size. The distribution of studies in the funnel plot revealed the presence of publication bias

A paper search yielded varying numbers of manuscripts from Southeast Asian countries. The Philippines had the fewest studies, while Thailand had the highest with 15 studies. No data was found for Brunei Darussalam and East Timor or Timor Leste on the human species.

The results of this study provide valuable insights into the seroprevalence of IgG and IgM antibodies against HEV in different populations across Southeast Asian countries. Understanding the prevalence of these antibodies is essential for assessing the burden of HEV infection and identifying high-risk groups.

The extensive analysis of anti-HEV IgG prevalence in this study covered a wide range of population groups in Southeast Asia, including the general population, blood donors, pregnant women, hospital patients, farm workers, and chronic patients. The results unveiled an overall pooled prevalence of 21.03%, indicating significant exposure to the Hepatitis E virus among individuals in the region at some point in their lives. Moreover, a consistent increase in IgG prevalence was observed over the years, with the highest prevalence occurring in the most recent decade (2011–2023). This suggests a progressive rise in HEV exposure within the region.

Upon examining the prevalence data across different decades and population cohorts, a uniform upward trend in HEV antibody prevalence became apparent across all groups. Several factors could be assessed as potential contributors to this trend:

Notably, the expanding population in Southeast Asian nations during this timeframe increased the number of individuals at risk of Hepatitis E infection.

The rapid urbanization, characterized by the migration from rural to urban areas, led to higher population density and conditions conducive to Hepatitis E virus transmission [ 84 ]. Access to clean drinking water and adequate sanitation facilities emerged as critical factors in preventing Hepatitis E. Regions with inadequate infrastructure, particularly in water and sanitation, faced an elevated risk due to contaminated water sources. Climate-related events, such as heavy rainfall and flooding, significantly impacted waterborne diseases like Hepatitis E. The increasing frequency and severity of such events emphasized the importance of considering climate-related factors in assessing prevalence trends [ 85 ]. Consumption of contaminated or undercooked meat, particularly pork, was identified as a source of Hepatitis E transmission. Changes in food consumption habits over time may have contributed to changes in seroprevalence [ 86 ]. Limited access to healthcare facilities in certain areas exacerbated the spread of Hepatitis E. Increased awareness together with advances in medical research and the establishment of robust surveillance systems likely improved the detection and reporting of Hepatitis E cases, contributing to the observed increase in seroprevalence [ 87 , 88 , 89 ]. These multifaceted factors have likely played a collective role in shaping the changing landscape of Hepatitis E seroprevalence in Southeast Asian nations over the past decades. The upward trend emphasizes the importance of continued monitoring, intervention, and public health measures to mitigate the spread of Hepatitis E in the region.

Among specific populations, pregnant women exhibited an IgG prevalence of 18.56%, indicating that a considerable number of pregnant individuals have been exposed to HEV. Pregnant women are particularly vulnerable to the consequences of HEV infection, as it can lead to severe outcomes for both the mother and the foetus.

Hospital patients with clinical signs of acute infection showed an IgG prevalence of 16.3%, suggesting that HEV is still a significant cause of acute hepatitis cases in the hospital setting. Similarly, farm workers, especially those exposed to animals (reservoirs of HEV), had a high prevalence of IgG (28.4%), highlighting the occupational risk associated with zoonotic transmission.

Chronic patients, including individuals with chronic liver disease, HIV infection, or solid organ transplantation, exhibited the highest pooled IgG prevalence among all cohorts at 29.2%. This finding underscores the importance of monitoring HEV infection in immunocompromised individuals, as they may develop chronic HEV infection, which can lead to severe liver complications.

The prevalence of IgM antibodies, which are indicative of recent or acute HEV infection, was lower overall compared to IgG. The general population showed an IgM prevalence of 2.63% among acute infection cases. Among hospital patients exhibiting clinical signs of acute infection, the prevalence of IgM antibodies indicative of recent or acute HEV infection was higher at 4.45%.

Farm workers, particularly those exposed to animals, demonstrated the highest IgM prevalence at 6.21%. This finding highlights the occupational risk of acquiring acute HEV infection in this population due to direct or indirect contact with infected animals.

The study also identified a high-risk group, consisting of farm workers and chronic patients, with a pooled IgG prevalence of 28.9% and an IgM prevalence of 4.42%. This group is particularly susceptible to HEV infection and requires targeted interventions to reduce transmission and prevent severe outcomes.

Overall, this study provides valuable data on the seroprevalence of HEV antibodies in different populations in Southeast Asian countries. It highlights the importance of continued surveillance and public health interventions to control HEV transmission, especially in vulnerable groups. Understanding the prevalence trends over time can aid in developing effective strategies for the prevention and management of HEV infections in the region. However, further research and studies are warranted to explore the underlying factors contributing to the observed seroprevalence trends and to design targeted interventions to reduce HEV transmission in specific populations. Among the countries of Southeast Asia Myanmar was the most for HEV infection, while Malaysia registered the lowest seroprevalence.

This study has some limitations that we should be aware of. We looked at studies in three languages (English, Russian, and French), but we couldn't find data from two out of the 11 countries. This means we might not have a complete picture of the disease's prevalence in the whole region.

The way we divided the groups based on occupation or status could be questioned. Different criteria might give us different results, so it's something we need to consider. Another challenge is that the study covers a long time from 1989 to 2023 by published research and involves many different countries. This makes it difficult to compare the results because the tests used, and the diagnostic abilities might have changed over time and vary across countries.

Despite these limitations, our study presents a detailed epidemiologic report of combined seroprevalence data for HEV in Southeast Asian countries following the UN division. It gives us a basic understanding of the disease's prevalence in the region and offers some insights into potential risk factors. However, to get a more accurate picture, future research should address these limitations and include data from all countries in the region. Furthermore, certain countries such as Myanmar and the Philippines have not reported HEV prevalence data since 2006 and 2015, respectively. The absence of recent HEV prevalence reports from certain countries raises concerns about the availability of up-to-date epidemiological data for assessing the current status of hepatitis E virus infections in these regions.

Our comprehensive analysis study involving Southeast Asian countries provides significant insights into the seroprevalence of hepatitis E virus (HEV) infection in this region and in various populations. The rates of anti-HEV antibodies observed among different groups, as well as the increasing trend in seroprevalence over decades, emphasize the dynamic nature of HEV transmission in the region. These findings contribute to a better understanding of HEV prevalence across countries, populations, and time periods in Southeast Asia, shedding light on important public health implications and suggesting directions for further research and intervention strategies.

Availability of data and materials

All data generated or analyzed during this study were included in this paper either in the results or supplementary information.

Abbreviations

Hepatitis E Virus

Preferred reporting items for systematic review and meta-analysis

Enzyme-Linked Immunosorbent Essay

Hepatitis E virus Immunoglobulin G

Hepatitis E Virus Immunoglobulin M

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Acknowledgements

The authors would like to thank all researchers of the primary research included in this study.

This work was supported by Project Research Center for Epidemiology and Prevention of Viral Hepatitis and Hepatocellular Carcinoma, Hiroshima University led by Prof. Junko Tanaka (PI).

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Ulugbek Khudayberdievich Mirzaev, Serge Ouoba, Ko Ko, Zayar Phyo, Chanroth Chhoung, Akuffo Golda Ataa, Aya Sugiyama, Tomoyuki Akita & Junko Tanaka

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UM, TA, and JT conceptualized the study. UM and SO contributed to developing the study design and data acquisition. UM, CC, ZP, AG, SO, and JT analysed and interpreted the data. UM, KK, and AS drafted the manuscript. TA, AS, KK, SO, and JT contributed to the intellectual content of the manuscript. All authors read and approved the final manuscript. JT and TA shared the co-correspondence. 

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Mirzaev, U.K., Ouoba, S., Ko, K. et al. Systematic review and meta-analysis of hepatitis E seroprevalence in Southeast Asia: a comprehensive assessment of epidemiological patterns. BMC Infect Dis 24 , 525 (2024). https://doi.org/10.1186/s12879-024-09349-2

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Electronic correlations drive the anomalous constitutive law between the structure and spectra of hydrogen bonds

Phys. rev. research, rui liu, xinrui yang, famin yu, depeng zhang, lu wang, ruhong zhou, and zhigang wang.

Classical constitutive law between the structure and spectra has long been established in most physical processes and behaviors. Despite the emerging consensus, whether this law applies to microscopic systems adhering to quantum mechanics remains a fundamental and open question, due to limitations in even the most state-of-the-art experimental techniques. Here, we report for the first time an anomalous constitutive law of hydrogen bonds (X-HY) using benchmark ab initio method. Notably, a donor X-H bond shortening occurred simultaneously with an unexpected redshift and enhanced intensity in IR spectra. The reason for donor X-H bond shortening is attributed to both the slowly increasing attractive force from acceptor Y atom and the increasing short-range repulsive forces from other protons attached to the approaching acceptor Y atom. Furthermore, neither eliminating vibrational mixing nor introducing various physical effects make vibrational spectra respond to X-H bond shortening. Another structural-characterization NMR spectra provide robust evidence for this anomalous law. This anomalous law is ascribed to the interplay of electronic correlations. Our Letter thus inspire a reassessment of paradigms, which broadens the scope of microscopic behavior for finer control.

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The Egyptian pyramid chain was built along the now abandoned Ahramat Nile Branch

• Eman Ghoneim   ORCID: orcid.org/0000-0003-3988-0335 1 ,
• Timothy J. Ralph   ORCID: orcid.org/0000-0002-4956-606X 2 ,
• Suzanne Onstine 3 ,
• Raghda El-Behaedi 4 ,
• Gad El-Qady 5 ,
• Amr S. Fahil 6 ,
• Mahfooz Hafez 5 ,
• Magdy Atya 5 ,
• Mohamed Ebrahim   ORCID: orcid.org/0000-0002-4068-5628 5 ,
• Ashraf Khozym 5 &
• Mohamed S. Fathy 6  

Communications Earth & Environment volume  5 , Article number:  233 ( 2024 ) Cite this article

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• Archaeology
• Geomorphology
• Hydrogeology
• Sedimentology

The largest pyramid field in Egypt is clustered along a narrow desert strip, yet no convincing explanation as to why these pyramids are concentrated in this specific locality has been given so far. Here we use radar satellite imagery, in conjunction with geophysical data and deep soil coring, to investigate the subsurface structure and sedimentology in the Nile Valley next to these pyramids. We identify segments of a major extinct Nile branch, which we name The Ahramat Branch, running at the foothills of the Western Desert Plateau, where the majority of the pyramids lie. Many of the pyramids, dating to the Old and Middle Kingdoms, have causeways that lead to the branch and terminate with Valley Temples which may have acted as river harbors along it in the past. We suggest that The Ahramat Branch played a role in the monuments’ construction and that it was simultaneously active and used as a transportation waterway for workmen and building materials to the pyramids’ sites.

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Introduction.

The landscape of the northern Nile Valley in Egypt, between Lisht in the south and the Giza Plateau in the north, was subject to a number of environmental and hydrological changes during the past few millennia 1 , 2 . In the Early Holocene (~12,000 years before present), the Sahara of North Africa transformed from a hyper-arid desert to a savannah-like environment, with large river systems and lake basins 3 , 4 due to an increase in global sea level at the end of the Last Glacial Maximum (LGM). The wet conditions of the Sahara provided a suitable habitat for people and wildlife, unlike in the Nile Valley, which was virtually inhospitable to humans because of the constantly higher river levels and swampy environment 5 . At this time, Nile River discharge was high, which is evident from the extensive deposition of organic-rich fluvial sediment in the Eastern Mediterranean basin 6 . Based on the interpretation of archeological material and pollen records, this period, known as the African Humid Period (AHP) (ca. 14,500–5000 years ago), was the most significant and persistent wet period from the early to mid-Holocene in the eastern Sahara region 7 , with an annual rainfall rate of 300–920 mm yr −1   8 . During this time the Nile would have had several secondary channels branching across the floodplain, similar to those described by early historians (e.g., Herodotus).

During the mid-Holocene (~10,000–6000 years ago), freshwater marshes were common within the Nile floodplain causing habitation to be more nucleated along the desert margins of the Nile Valley 9 . The desert margins provided a haven from the high Nile water. With the ending of the AHP and the beginning of the Late Holocene (~5500 years ago to present), rainfall greatly declined, and the region’s humid phase gradually came to an end with punctuated short wet episodes 10 . Due to increased aridity in the Sahara, more people moved out of the desert towards the Nile Valley and settled along the edge of the Nile floodplain. With the reduced precipitation, sedimentation increased in and around the Nile River channels causing the proximal floodplain to rise in height and adjacent marshland to decrease in the area 11 , 12 estimated the Nile flood levels to have ranged from 1 to 4 m above the baseline (~5000 BP). Inhabitants moved downhill to the Nile Valley and settled in the elevated areas on the floodplain, including the raised natural levees of the river and jeziras (islands). This was the beginning of the Old Kingdom Period (ca. 2686 BCE) and the time when early pyramid complexes, including the Step Pyramid of Djoser, were constructed at the margins of the floodplain. During this time the Nile discharge was still considerably higher than its present level. The high flow of the river, particularly during the short-wet intervals, enabled the Nile to maintain multiple branches, which meandered through its floodplain. Although the landscape of the Nile floodplain has greatly transformed due to river regulation associated with the construction of the Aswan High Dam in the 1960s, this region still retains some clear hydro-geomorphological traces of the abandoned river channels.

Since the beginning of the Pharaonic era, the Nile River has played a fundamental role in the rapid growth and expansion of the Egyptian civilization. Serving as their lifeline in a largely arid landscape, the Nile provided sustenance and functioned as the main water corridor that allowed for the transportation of goods and building materials. For this reason, most of the key cities and monuments were in close proximity to the banks of the Nile and its peripheral branches. Over time, however, the main course of the Nile River laterally migrated, and its peripheral branches silted up, leaving behind many ancient Egyptian sites distant from the present-day river course 9 , 13 , 14 , 15 . Yet, it is still unclear as to where exactly the ancient Nile courses were situated 16 , and whether different reaches of the Nile had single or multiple branches that were simultaneously active in the past. Given the lack of consensus amongst scholars regarding this subject, it is imperative to develop a comprehensive understanding of the Nile during the time of the ancient Egyptian civilization. Such a poor understanding of Nile River morphodynamics, particularly in the region that hosts the largest pyramid fields of Egypt, from Lisht to Giza, limits our understanding of how changes in the landscape influenced human activities and settlement patterns in this region, and significantly restricts our ability to understand the daily lives and stories of the ancient Egyptians.

Currently, much of the original surface of the ancient Nile floodplain is masked by either anthropogenic activity or broad silt and sand sheets. For this reason, singular approaches such as on-ground searches for the remains of hidden former Nile branches are both increasingly difficult and inauspicious. A number of studies have already been carried out in Egypt to locate segments of the ancient Nile course. For instance 9 , proposed that the axis of the Nile River ran far west of its modern course past ancient cities such as el-Ashmunein (Hermopolis) 13 . mapped the ancient hydrological landscape in the Luxor area and estimated both an eastward and westward Nile migration rate of 2–3 km per 1000 years. In the Nile Delta region 17 , detected several segments of buried Nile distributaries and elevated mounds using geoelectrical resistivity surveys. Similarly, a study by Bunbury and Lutley 14 identified a segment of an ancient Nile channel, about 5000 years old, near the ancient town of Memphis ( men-nefer ). More recently 15 , used cores taken around Memphis to reveal a section of a lateral ancient Nile branch that was dated to the Neolithic and Predynastic times (ca. 7000–5000 BCE). On the bank of this branch, Memphis, the first capital of unified Egypt, was founded in early Pharaonic times. Over the Dynastic period, this lateral branch then significantly migrated eastwards 15 . A study by Toonen et al. 18 , using borehole data and electrical resistivity tomography, further revealed a segment of an ancient Nile branch, dating to the New Kingdom Period, situated near the desert edge west of Luxor. This river branch would have connected important localities and thus played a significant role in the cultural landscape of this area. More recent research conducted further north by Sheisha et al. 2 , near the Giza Plateau, indicated the presence of a former river and marsh-like environment in the floodplain east of the three great Pyramids of Giza.

Even though the largest concentration of pyramids in Egypt are located along a narrow desert strip from south Lisht to Giza, no explanation has been offered as to why these pyramid fields were condensed in this particular area. Monumental structures, such as pyramids and temples, would logically be built near major waterways to facilitate the transportation of their construction materials and workers. Yet, no waterway has been found near the largest pyramid field in Egypt, with the Nile River lying several kilometers away. Even though many efforts to reconstruct the ancient Nile waterways have been conducted, they have largely been confined to small sites, which has led to the mapping of only fragmented sections of the ancient Nile channel systems.

In this work, we present remote sensing, geomorphological, soil coring and geophysical evidence to support the existence of a long-lost ancient river branch, the Ahramat Branch, and provide the first map of the paleohydrological setting in the Lisht-Giza area. The finding of the Ahramat Branch is not only crucial to our understanding of why the pyramids were built in these specific geographical areas, but also for understanding how the pyramids were accessed and constructed by the ancient population. It has been speculated by many scholars that the ancient Egyptians used the Nile River for help transporting construction materials to pyramid building sites, but until now, this ancient Nile branch was not fully uncovered or mapped. This work can help us better understand the former hydrological setting of this region, which would in turn help us learn more about the environmental parameters that may have influenced the decision to build these pyramids in their current locations during the time of Pharaonic Egypt.

Position and morphology of the Ahramat Branch

Synthetic Aperture Radar (SAR) imagery and radar high-resolution elevation data for the Nile floodplain and its desert margins, between south Lisht and the Giza Plateau area, provide evidence for the existence of segments of a major ancient river branch bordering 31 pyramids dating from the Old Kingdom to Second Intermediate Period (2686−1649 BCE) and spanning between Dynasties 3–13 (Fig.  1a ). This extinct branch is referred to hereafter as the Ahramat Branch, meaning the “Pyramids Branch” in Arabic. Although masked by the cultivated fields of the Nile floodplain, subtle topographic expressions of this former branch, now invisible in optical satellite data, can be traced on the ground surface by TanDEM-X (TDX) radar data and the Topographic Position Index (TPI). Data analysis indicates that this lateral distributary channel lies between 2.5 and 10.25 km west from the modern Nile River. The branch appears to have a surface channel depth between 2 and 8 m, a channel length of about 64 km and a channel width of 200–700 m, which is similar to the width of the contemporary neighboring Nile course. The size and longitudinal continuity of the Ahramat Branch and its proximity to all the pyramids in the study area implies a functional waterway of great significance.

a Shows the Ahramat Branch borders a large number of pyramids dating from the Old Kingdom to the 2 nd Intermediate Period and spanning between Dynasties 3 and 13. b Shows Bahr el-Libeini canal and remnant of abandoned channel visible in the 1911 historical map (Egyptian Survey Department scale 1:50,000). c Bahr el-Libeini canal and the abandoned channel are overlain on satellite basemap. Bahr el-Libeini is possibly the last remnant of the Ahramat Branch before it migrated eastward. d A visible segment of the Ahramat Branch in TDX is now partially occupied by the modern Bahr el-Libeini canal. e A major segment of the Ahramat Branch, approximately 20 km long and 0.5 km wide, can be traced in the floodplain along the Western Desert Plateau south of the town of Jirza. Location of e is marked in white a box in a . (ESRI World Image Basemap, source: Esri, Maxar, Earthstar Geographics).

A trace of a 3 km river segment of the Ahramat Branch, with a width of about 260 m, is observable in the floodplain west of the Abu Sir pyramids field (Fig.  1b–d ). Another major segment of the Ahramat Branch, approximately 20 km long and 0.5 km wide can be traced in the floodplain along the Western Desert Plateau south of the town of Jirza (Fig.  1e ). The visible segments of the Ahramat Branch in TDX are now partially occupied by the modern Bahr el-Libeini canal. Such partial overlap between the courses of this canal, traced in the1911 historical maps (Egyptian Survey Department scale 1:50,000), and the Ahramat Branch is clear in areas where the Nile floodplain is narrower (Fig.  1b–d ), while in areas where the floodplain gets wider, the two water courses are about 2 km apart. In light of that, Bahr el-Libeini canal is possibly the last remnant of the Ahramat Branch before it migrated eastward, silted up, and vanished. In the course of the eastward migration over the Nile floodplain, the meandering Ahramat Branch would have left behind traces of abandoned channels (narrow oxbow lakes) which formed as a result of the river erosion through the neck of its meanders. A number of these abandoned channels can be traced in the 1911 historical maps near the foothill of the Western Desert plateau proving the eastward shifting of the branch at this locality (Fig.  1b–d ). The Dahshur Lake, southwest of the city of Dahshur, is most likely the last existing trace of the course of the Ahramat Branch.

Subsurface structure and sedimentology of the Ahramat Branch

Geophysical surveys using Ground Penetrating Radar (GPR) and Electromagnetic Tomography (EMT) along a 1.2 km long profile revealed a hidden river channel lying 1–1.5 m below the cultivated Nile floodplain (Fig.  2 ). The position and shape of this river channel is in an excellent match with those derived from radar satellite imagery for the Ahramat Branch. The EMT profile shows a distinct unconformity in the middle, which in this case indicates sediments that have a different texture than the overlying recent floodplain silt deposits and the sandy sediments that are adjacent to this former branch (Fig.  2 ). GPR overlapping the EMT profile from 600–1100 m on the transect confirms this. Here, we see evidence of an abandoned riverbed approximately 400 m wide and at least 25 m deep (width:depth ratio ~16) at this location. This branch has a symmetrical channel shape and has been infilled with sandy Neonile sediment different to other surrounding Neonile deposits and the underlying Eocene bedrock. The geophysical profile interpretation for the Ahramat Branch at this locality was validated using two sediment cores of depths 20 m (Core A) and 13 m (Core B) (Fig.  3 ). In Core A between the center and left bank of the former branch we found brown sandy mud at the floodplain surface and down to ~2.7 m with some limestone and chert fragments, a reddish sandy mud layer with gravel and handmade material inclusions at ~2.8 m, a gray sandy mud layer from ~3–5.8 m, another reddish sandy mud layer with gravel and freshwater mussel shells at ~6 m, black sandy mud from ~6–8 m, and sandy silt grading into clean, well-sorted medium sand dominated the profile from ~8 to >13 m. In Core B on the right bank of the former branch we found recently deposited brown sandy mud at the floodplain surface and down to ~1.5 m, alternating brown and gray layers of silty and sandy mud down to ~4 m (some reddish layers with gravel and handmade material inclusions), a black sandy mud layer from ~4–4.9 m, and another reddish sandy mud layer with gravel and freshwater mussel shells at ~5 m, before clean, well-sorted medium sand dominated the profile from 5 to >20 m. Shallow groundwater was encountered in both cores concurrently with the sand layers, indicating that the buried sedimentary structure of the abandoned Ahramat Branch acts as a conduit for subsurface water flow beneath the distal floodplain of the modern Nile River.

a Locations of geophysical profile and soil drilling (ESRI World Image Basemap, source: Esri, Maxar, Earthstar Geographics). Photos taken from the field while using the b Electromagnetic Tomography (EMT) and c Ground Penetrating Radar (GPR). d Showing the apparent conductivity profile, e showing EMT profile, and f showing GPR profiles with overlain sketch of the channel boundary on the GPR graph. g Simplified interpretation of the buried channel with the location of the two-soil coring of A and B.

It shows two-soil cores, A and core B, with soil profile descriptions, graphic core logs, sediment grain size charts, and example photographs.

Alignment of old and middle kingdom pyramids to the Ahramat Branch

The royal pyramids in ancient Egypt are not isolated monuments, but rather joined with several other structures to form complexes. Besides the pyramid itself, the pyramid complex includes the mortuary temple next to the pyramid, a valley temple farther away from the pyramid on the edge of a waterbody, and a long sloping causeway that connects the two temples. A causeway is a ceremonial raised walkway, which provides access to the pyramid site and was part of the religious aspects of the pyramid itself 19 . In the study area, it was found that many of the causeways of the pyramids run perpendicular to the course of the Ahramat Branch and terminate directly on its riverbank.

In Egyptian pyramid complexes, the valley temples at the end of causeways acted as river harbors. These harbors served as an entry point for the river borne visitors and ceremonial roads to the pyramid. Countless valley temples in Egypt have not yet been found and, therefore, might still be buried beneath the agricultural fields and desert sands along the riverbank of the Ahramat Branch. Five of these valley temples, however, partially survived and still exist in the study area. These temples include the valley temples of the Bent Pyramid, the Pyramid of Khafre, and the Pyramid of Menkaure from Dynasty 4; the valley temple of the Pyramid of Sahure from Dynasty 5, and the valley temple of the Pyramid of Pepi II from Dynasty 6. All the aforementioned temples are dated to the Old Kingdom. These five surviving temples were found to be positioned adjacent to the riverbank of the Ahramat Branch, which strongly implies that this river branch was contemporaneously functioning during the Old Kingdom, at the time of pyramid construction.

Analysis of the ground elevation of the 31 pyramids and their proximity to the floodplain, within the study area, helped explain the position and relative water level of the Ahramat Branch during the time between the Old Kingdom and Second Intermediate Period (ca. 2649–1540 BCE). Based on Fig. ( 4) , the Ahramat Branch had a high-water level during the first part of the Old Kingdom, especially during Dynasty 4. This is evident from the high ground elevation and long distance from the floodplain of the pyramids dated to that period. For instance, the remote position of the Bent and Red Pyramids in the desert, very far from the Nile floodplain, is a testament to the branch’s high-water level. On the contrary, during the Old Kingdom, our data demonstrated that the Ahramat Branch would have reached its lowest level during Dynasty 5. This is evident from the low altitudes and close proximity to the floodplain of most Dynasty 5 pyramids. The orientation of the Sahure Pyramid’s causeway (Dynasty 5) and the location of its valley temple in the low-lying floodplain provide compelling evidence for the relatively low water level proposition of the Ahramat Branch during this stage. The water level of the Ahramat Branch would have been slightly raised by the end of Dynasty 5 (the last 15–30 years), during the reign of King Unas and continued to rise during Dynasty 6. The position of Pepi II and Merenre Pyramids (Dynasty 6) deep in the desert, west of the Djedkare Isesi Pyramid (Dynasty 5), supports this notion.

It explains the position and relative water level of the Ahramat Branch during the time between the Old Kingdom and Second Intermediate Period. a Shows positive correlation between the ground elevation of the pyramids and their proximity to the floodplain. b Shows positive correlation between the average ground elevation of the pyramids and their average proximity to the floodplain in each Dynasty. c Illustrates the water level interpretation by Hassan (1986) in Faiyum Lake in correlation to the average pyramids ground elevation and average distances to the floodplain in each Dynasty. d The data indicates that the Ahramat Branch had a high-water level during the first period of the Old Kingdom, especially during Dynasty 4. The water level reduced afterwards but was raised slightly in Dynasty 6. The position of the Middle Kingdom’s pyramids, which was at lower altitudes and in close proximity to the floodplain as compared to those of the Old Kingdom might be explained by the slight eastward migration of the Ahramat Branch.

In addition, our analysis in Fig. ( 4) , shows that the Qakare Ibi Pyramid of Dynasty 8 was constructed very close to the floodplain on very low elevation, which implies that the Nile water levels were very low at this time of the First Intermediate Period (2181–2055 BCE). This finding is in agreement with previous work conducted by Kitchen 20 which implies that the sudden collapse of the Old Kingdom in Egypt (after 4160 BCE) was largely caused by catastrophic failure of the annual flood of the Nile River for a period of 30–40 years. Data from soil cores near Memphis indicated that the Old Kingdom settlement is covered by about 3 m of sand 11 . Accordingly, the Ahramat Branch was initially positioned further west during the Old Kingdom and then shifted east during the Middle Kingdom due to the drought-induced sand encroachments of the First Intermediate Period, “a period of decentralization and weak pharaonic rule” in ancient Egypt, spanning about 125 years (2181–2055 BCE) post Old Kingdom era. Soil cores from the drilling program at Memphis show dominant dry conditions during the First Intermediate Period with massive eolian sand sheets extended over a distance of at least 0.5 km from the edge of the western desert escarpment 21 . The Ahramat Branch continued to move east during the Second Intermediate Period until it had gradually lost most of its water supply by the New Kingdom.

The western tributaries of the Ahramat Branch

Sentinal-1 radar data unveiled several wide channels (inlets) in the Western Desert Plateau connected to the Ahramat Branch. These inlets are currently covered by a layer of sand, thus partially invisible in multispectral satellite imagery. In Sentinal-1 radar imagery, the valley floors of these inlets appear darker than the surrounding surfaces, indicating subsurface fluvial deposits. These smooth deposits appear dark owing to the specular reflection of the radar signals away from the receiving antenna (Fig.  5a, b ) 22 . Considering that Sentinel-1’s C-Band has a penetration capability of approximately 50 cm in dry sand surface 23 , this would suggest that the riverbed of these channels is covered by at least half a meter of desert sand. Unlike these former inlets, the course of the Ahramat Branch is invisible in SAR data due in large part to the presence of dense farmlands in the floodplain, which limits radar penetration and the detection of underlying fluvial deposition. Moreover, the radar topographic data from TDX revealed the areal extent of these inlets. Their river courses were extracted from TDX data using the Topographic Position Index (TPI), an algorithm which is used to compute the topographic slope positions and to automate landform classifications (Fig.  5c, d ). Negative TPI values show the former riverbeds of the inlets, while positive TPI signify the riverbanks bordering them.

a Conceptual sketch of the dependence of surface roughness on the sensor wavelength λ (modified after 48 ). b Expected backscatter characteristics in sandy desert areas with buried dry riverbeds. c Dry channels/inlets masked by desert sand in the Dahshur area. d The channels’ courses were extracted using TPI. Negative TPI values highlight the courses of the channels while positive TPI signify their banks.

Analysis indicated that several of the pyramid’s causeways, from Dynasties 4 and 6, lead to the inlet’s riverbanks (Fig.  6 ). Among these pyramids, are the Bent Pyramid, the first pyramid built by King Snefru in Dynasty 4 and among the oldest, largest, and best preserved ancient Egyptian pyramids that predates the Giza Pyramids. This pyramid is situated at the royal necropolis of Dahshur. The position of the Bent Pyramid, deep in the desert, far from the modern Nile floodplain, remained unexplained by researchers. This pyramid has a long causeway (~700 m) that is paved in the desert with limestone blocks and is attached to a large valley temple. Although all the pyramids’ valley temples in Egypt are connected to a water body and served as the landing point of all the river-borne visitors, the valley temple of the Bent Pyramid is oddly located deep in the desert, very distant from any waterways and more than 1 km away from the western edge of the modern Nile floodplain. Radar data revealed that this temple overlooked the bank of one of these extinct channels (called Wadi al-Taflah in historical maps). This extinct channel (referred to hereafter as the Dahshur Inlet due to its geographical location) is more than 200 m wide on average (Fig.  6 ). In light of this finding, the Dahshur Inlet, and the Ahramat Branch, are thus strongly argued to have been active during Dynasty 4 and must have played an important role in transporting building materials to the Bent Pyramid site. The Dahshur Inlet could have also served the adjacent Red Pyramid, the second pyramid built by the same king (King Snefru) in the Dahshur area. Yet, no traces of a causeway nor of a valley temple has been found thus far for the Red Pyramid. Interestingly, pyramids in this site dated to the Middle Kingdom, including the Amenemhat III pyramid, also known as the Black Pyramid, White Pyramid, and Pyramid of Senusret III, are all located at least 1 km far to the east of the Dynasty 4 pyramids (Bent and Red) near the floodplain (Fig.  6 ), which once again supports the notion of the eastward shift of the Ahramat Branch after the Old Kingdom.

a The two inlets are presently covered by sand, thus invisible in optical satellite imagery. b Radar data, and c TDX topographic data reveal the riverbed of the Sakkara Inlet due to radar signals penetration capability in dry sand. b and c show the causeways of Pepi II and Merenre Pyramids, from Dynasty 6, leading to the Saqqara Inlet. The Valley Temple of Pepi II Pyramid overlooks the inlet riverbank, which indicates that the inlet, and thus Ahramat Branch, were active during Dynasty 6. d Radar data, and e TDX topographic data, reveal the riverbed of the Dahshur Inlet with the Bent Pyramid’s causeway of Dynasty 4 leading to the Inlet. The Valley Temple of the Bent Pyramid overlooks the riverbank of the Dahshur Inlet, which indicates that the inlet and the Ahramat Branch were active during Dynasty 4 of the Old Kingdom.

Radar satellite data revealed yet another sandy buried channel (tributary), about 6 km north of the Dahshur Inlet, to the west of the ancient city of Memphis. This former fluvial channel (referred to hereafter as the Saqqara Inlet due to its geographical location) connects to the Ahramat Branch with a broad river course of more than 600 m wide. Data shows that the causeways of the two pyramids of Pepi II and Merenre, situated at the royal necropolis of Saqqara and dated to Dynasty 6, lead directly to the banks of the Saqqara Inlet (see Fig.  6 ). The 400 m long causeway of Pepi II pyramid runs northeast over the southern Saqqara plateau and connects to the riverbank of the Saqqara Inlet from the south. The causeway terminates with a valley temple that lies on the inlet’s riverbank. The 250 long causeway of the Pyramid of Merenre runs southeast over the northern Saqqara plateau and connects to the riverbank of the Saqqara Inlet from the north. Since both pyramids dated to Dynasty 6, it can be argued that the water level of the Ahramat Branch was higher during this period, which would have flooded at least the entrance of its western inlets. This indicates that the downstream segment of the Saqqara Inlet was active during Dynasty 6 and played a vital role in transporting construction materials and workers to the two pyramids sites. The fact that none of the Dynasty 5 pyramids in this area (e.g., the Djedkare Isesi Pyramid) were positioned on the Saqqara Inlet suggests that the water level in the Ahramat Branch was not high enough to enter and submerge its inlets during this period.

In addition, our data analysis clearly shows that the causeways of the Khafre, Menkaure, and Khentkaus pyramids, in the Giza Plateau, lead to a smaller but equally important river bay associated with the Ahramat Branch. This lagoon-like river arm is referred to here as the Giza Inlet (Fig.  7 ). The Khufu Pyramid, the largest pyramid in Egypt, seems to be connected directly to the river course of the Ahramat Branch (Fig.  7 ). This finding proves once again that the Ahramat Branch and its western inlets were hydrologically active during Dynasty 4 of the Old Kingdom. Our ancient river inlet hypothesis is also in accordance with earlier research, conducted on the Giza Plateau, which indicates the presence of a river and marsh-like environment in the floodplain east of the Giza pyramids 2 .

The causeways of the four Pyramids lead to an inlet, which we named the Giza Inlet, that connects from the west with the Ahramat Branch. These causeways connect the pyramids with valley temples which acted as river harbors in antiquity. These river segments are invisible in optical satellite imagery since they are masked by the cultivated lands of the Nile floodplain. The photo shows the valley temple of Khafre Pyramid (Photo source: Author Eman Ghoneim).

During the Old Kingdom Period, our analysis suggests that the Ahramat Branch had a high-water level during the first part, especially during Dynasty 4 whereas this water level was significantly decreased during Dynasty 5. This finding is in agreement with previous studies which indicate a high Nile discharge during Dynasty 4 (e.g., ref. 24 ). Sediment isotopic analysis of the Nile Delta indicated that Nile flows decrease more rapidly by the end of Dynasty 4 25 , in addition 26 reported that during Dynasties 5 and 6 the Nile flows were the lowest of the entire Dynastic period. This long-lost Ahramat Branch (possibly a former Yazoo tributary to the Nile) was large enough to carry a large volume of the Nile discharge in the past. The ancient channel segment uncovered by 1 , 15 west of the city of Memphis through borehole logs is most likely a small section of the large Ahramat Branch detected in this study. In the Middle Kingdom, although previous studies implied that the Nile witnessed abundant flood with occasional failures (e.g., ref. 27 ), our analysis shows that all the pyramids from the Middle Kingdom were built far east of their Old Kingdom counterparts, on lower altitudes and in close proximity to the floodplain as compared to those of the Old Kingdom. This paradox might be explained by the fact that the Ahramat Branch migrated eastward, slightly away from the Western Desert escarpment, prior to the construction of the Middle Kingdom pyramids, resulting in the pyramids being built eastward so that they could be near the waterway.

The eastward migration and abandonment of the Ahramat Branch could be attributed to gradual tilting of the Nile delta and floodplain in lower Egypt towards the northeast due to tectonic activity 28 . A topographic tilt such as this would have accelerated river movement eastward due to the river being located in the west at a relatively higher elevation of the floodplain. While near-channel floodplain deposition would naturally lead to alluvial ridge development around the active Ahramat Branch, and therefore to lower-lying tracts of adjacent floodplain to the east, regional tilting may explain the wholesale lateral migration of the river in that direction. The eastward migration and abandonment of the branch could also be ascribed to sand incursion due to the branch’s proximity to the Western Desert Plateau, where windblown sand is abundant. This would have increased sand deposition along the riverbanks and caused the river to silt up, particularly during periods of low flow. The region experienced drought during the First Intermediate Period, prior to the Middle Kingdom. In the area of Abu Rawash north 29 and Dahshur site 11 , settlements from the Early Dynastic and Old Kingdom were found to be covered by more than 3 m of desert sands. During this time, windblown sand engulfed the Old Kingdom settlements and desert sands extended eastward downhill over a distance of at least 0.5 km 21 . The abandonment of sites at Abusir (5 th Dynasty), where the early pottery-rich deposits are covered by wind-blown sand and then mud without sherds, can be used as evidence that the Ahramat Branch migrated eastward after the Old Kingdom. The increased sand deposition activity, during the end of the Old Kingdom, and throughout the First Intermediate Period, was most likely linked to the period of drought and desertification of the Sahara 30 . In addition, the reduced river discharge caused by decreased rainfall and increased aridity in the region would have gradually reduced the river course’s capacity, leading to silting and abandonment of the Ahramat Branch as the river migrated to the east.

The Dahshur, Saqqara, and Giza inlets, which were connected to the Ahramat Branch from the west, were remnants of past active drainage systems dated to the late Tertiary or the Pleistocene when rainwater was plentiful 31 . It is proposed that the downstream reaches of these former channels (wadis) were submerged during times of high-water levels of the Ahramat Branch, forming long narrow water arms (inlets) that gave a wedge-like shape to the western flank of the Ahramat Branch. During the Old Kingdom, the waters of these inlets would have flowed westward from the Ahramat Branch rather than from their headwaters. As the drought intensified during the First Intermediate Period, the water level of the Ahramat Branch was lowered and withdrew from its western inlets, causing them to silt up and eventually dry out. The Dahshur, Saqqara, and Giza inlets would have provided a bay environment where the water would have been calm enough for vessels and boats to dock far from the busy, open water of the Ahramat Branch.

Sediments from the Ahramat Branch riverbed, which were collected from the two deep soil cores (cores A and B), show an abrupt shift from well-sorted medium sands at depth to overlying finer materials with layers including gravel, shell, and handmade materials. This indicates a step-change from a relatively consistent higher-energy depositional regime to a generally lower-energy depositional regime with periodic flash floods at these sites. So, the Ahramat Branch in this region carried and deposited well-sorted medium sand during its last active phase, and over time became inactive, infilling with sand and mud until an abrupt change led the (by then) shallow depression fill with finer distal floodplain sediment (possibly in a wetland) that was utilized by people and experienced periodic flash flooding. Validation of the paleo-channel position and sediment type using these cores shows that the Ahramat Branch has similar morphological features and an upward-fining depositional sequence as that reported near Giza, where two cores were previously used to reconstruct late Holocene Nile floodplain paleo-environments 2 . Further deep soil coring could determine how consistent the geomorphological features are along the length of the Ahramat branch, and to help explain anomalies in areas where the branch has less surface expression and where remote sensing and geophysical techniques have limitations. Considering more core logs can give a better understanding of the floodplain and the buried paleo-channels.

The position of the Ahramat Branch along the western edge of the Nile floodplain suggests it to be the downstream extension of Bahr Yusef. In fact, Bahr Yusef’s course may have initially flowed north following the natural surface gradient of the floodplain before being forced to turn west to flow into the Fayum Depression. This assumption could be supported by the sharp westward bend of Bahr Yusef’s course at the entrance to the Fayum Depression, which could be a man-made attempt to change the waterflow direction of this branch. According to Römer 32 , during the Middle Kingdom, the Gadallah Dam located at the entrance of the Fayum, and a possible continuation running eastwards, blocked the flow of Bahr Yusef towards the north. However, a sluice, probably located near the village of el-Lahun, was created in order to better control the flow of water into the Fayum. When the sluice was locked, the water from Bahr Yusef was directed to the west and into the depression, and when the sluice was open, the water would flow towards the north via the course of the Ahramat Branch. Today, the abandoned Ahramat Branch north of Fayum appears to support subsurface water flow in the buried coarse sand bed layers, however these shallow groundwater levels are likely to be quite variable due to proximity of the bed layers to canals and other waterways that artificially maintain shallow groundwater. Groundwater levels in the region are known to be variable 33 , but data on shallow groundwater could be used to further validate the delineated paleo-channel of the Ahramat Branch.

The present work enabled the detection of segments of a major former Nile branch running at the foothills of the Western Desert Plateau, where the vast majority of the Ancient Egyptian pyramids lie. The enormity of this branch and its proximity to the pyramid complexes, in addition to the fact that the pyramids’ causeways terminate at its riverbank, all imply that this branch was active and operational during the construction phase of these pyramids. This waterway would have connected important locations in ancient Egypt, including cities and towns, and therefore, played an important role in the cultural landscape of the region. The eastward migration and abandonment of the Ahramat Branch could be attributed to gradual movement of the river to the lower-lying adjacent floodplain or tilting of the Nile floodplain toward the northeast as a result of tectonic activity, as well as windblown sand incursion due to the branch’s proximity to the Western Desert Plateau. The increased sand deposition was most likely related to periods of desertification of the Great Sahara in North Africa. In addition, the branch eastward movement and diminishing could be explained by the reduction of the river discharge and channel capacity caused by the decreased precipitation and increased aridity in the region, particularly during the end of the Old Kingdom.

The integration of radar satellite data with geophysical surveying and soil coring, which we utilized in this study, is a highly adaptable approach in locating similar former buried river systems in arid regions worldwide. Mapping the hidden course of the Ahramat Branch, allowed us to piece together a more complete picture of ancient Egypt’s former landscape and a possible water transportation route in Lower Egypt, in the area between Lisht and the Giza Plateau.

Revealing this extinct Nile branch can provide a more refined idea of where ancient settlements were possibly located in relation to it and prevent them from being lost to rapid urbanization. This could improve the protection measures of Egyptian cultural heritage. It is the hope that our findings can improve conservation measures and raise awareness of these sites for modern development planning. By understanding the landscape of the Nile floodplain and its environmental history, archeologists will be better equipped to prioritize locations for fieldwork investigation and, consequently, raise awareness of these sites for conservation purposes and modern development planning. Our finding has filled a much-needed knowledge gap related to the dominant waterscape in ancient Egypt, which could help inform and educate a wide array of global audiences about how earlier inhabitants were living and in what ways shifts in their landscape drove human activity in such an iconic region.

Materials and methods

The work comprised of two main elements: satellite remote sensing and historical maps and geophysical survey and sediment coring, complemented by archeological resources. Using this suite of investigative techniques provided insights into the nature and relationship of the former Ahramat Branch with the geographical location of the pyramid complexes in Egypt.

Satellite remote sensing and historical maps

Unlike optical sensors that image the land surface, radar sensors image the subsurface due to their unique ability to penetrate the ground and produce images of hidden paleo-rivers and structures. In this context, radar waves strip away the surface sand layer and expose previously unidentified buried channels. The penetration capability of radar waves in the hyper-arid regions of North Africa is well documented 4 , 34 , 35 , 36 , 37 . The penetration depth varies according to the radar wavelength used at the time of imaging. Radar signal penetration becomes possible without significant attenuation if the surface cover material is extremely dry (<1% moisture content), fine grained (<1/5 of the imaging wavelength) and physically homogeneous 23 . When penetrating desert sand, radar signals have the ability to detect subsurface soil roughness, texture, compactness, and dielectric properties 38 . We used the European Space Agency (ESA) Sentinel-1 data, a radar satellite constellation consisting of a C-Band synthetic aperture radar (SAR) sensor, operating at 5.405 GHz. The Sentinel-1 SAR image used here was acquired in a descending orbit with an interferometric wide swath mode (IW) at ground resolutions of 5 m × 20 m, and dual polarizations of VV + VH. Since Sentinal-1 is operated in the C-Band, it has an estimated penetration depth of 50 cm in very dry, sandy, loose soils 39 . We used ENVI v. 5.7 SARscape software for processing radar imagery. The used SAR processing sequences have generated geo-coded, orthorectified, terrain-corrected, noise free, radiometrically calibrated, and normalized Sentinel-1 images with a pixel size of 12.5 m. In SAR imagery subsurface fluvial deposits appear dark owing to specular reflection of the radar signals away from the receiving antenna, whereas buried coarse and compacted material, such as archeological remains appear bright due to diffuse reflection of radar signals 40 .

Other previous studies have shown that combining radar topographic imagery (e.g., Shuttle Radar Topography Mission-SRTM) with SAR images improves the extraction and delineation of mega paleo-drainage systems and lake basins concealed under present-day topographic signatures 3 , 4 , 22 , 41 . Topographic data represents a primary tool in investigating surface landforms and geomorphological change both spatially and temporally. This data is vital in mapping past river systems due to its ability to show subtle variations in landform morphology 37 . In low lying areas, such as the Nile floodplain, detailed elevation data can detect abandoned channels, fossilized natural levees, river meander scars and former islands, which are all crucial elements for reconstructing the ancient Nile hydrological network. In fact, the modern topography in many parts of the study area is still a good analog of the past landscape. In the present study, TanDEM-X (TDX) topographic data, from the German Aerospace Centre (DLR), has been utilized in ArcGIS Pro v. 3.1 software due to its fine spatial resolution of 0.4 arc-second ( ∼ 12 m). TDX is based on high frequency X-Band Synthetic Aperture Radar (SAR) (9.65 GHz) and has a relative vertical accuracy of 2 m for areas with a slope of ≤20% 42 . This data was found to be superior to other topographic DEMs (e.g., Shuttle Radar Topography Mission and ASTER Global Digital Elevation Map) in displaying fine topographic features even in the cultivated Nile floodplain, thus making it particularly well suited for this study. Similar archeological investigations using TDX elevation data in the flat terrains of the Seyhan River in Turkey and the Nile Delta 43 , 44 allowed for the detection of levees and other geomorphologic features in unprecedented spatial resolution. We used the Topographic Position Index (TPI) module of 45 with the TDX data by applying varying neighboring radiuses (20–100 m) to compute the difference between a cell elevation value and the average elevation of the neighborhood around that cell. TPI values of zero are either flat surfaces with minimal slope, or surfaces with a constant gradient. The TPI can be computed using the following expression 46 .

Where the scaleFactor is the outer radius in map units and Irad and Orad are the inner and outer radius of annulus in cells. Negative TPI values highlight abandoned riverbeds and meander scars, while positive TPI signify the riverbanks and natural levees bordering them.

The course of the Ahramat Branch was mapped from multiple data sources and used different approaches. For instance, some segments of the river course were derived automatically using the TPI approach, particularly in the cultivated floodplain, whereas others were mapped using radar roughness signatures specially in sandy desert areas. Moreover, a number of abandoned channel segments were digitized on screen from rectified historical maps (Egyptian Survey Department scale 1:50,000 collected on years 1910–1911) near the foothill of the Western Desert Plateau. These channel segments together with the former river course segments delineated from radar and topographic data were aggregated to generate the former Ahramat Branch. In addition to this and to ensure that none of the channel segments of the Ahramat Branch were left unmapped during the automated process, a systematic grid-based survey (through expert’s visual observation) was performed on the satellite data. Here, Landsat 8 and Sentinal-2 multispectral images, Sentinal-1 radar images and TDX topographic data were used as base layers, which were thoroughly examined, grid-square by grid-square (2*2 km per a square) at a full resolution, in order to identify small-scale fluvial landforms, anomalous agricultural field patterns and irregular ditches, and determine their spatial distributions. Here, ancient fluvial channels were identified using two key aspects: First, the sinuous geometry of natural and manmade features and, second the color tone variations in the satellite imagery. For example, clusters of contiguous pixels with darker tones and sinuous shapes may signify areas of a higher moisture content in optical imagery, and hence the possible existence of a buried riverbed. Stretching and edge detection were applied to enhance contrasts in satellite images brightness to enable the visualization of traces of buried river segments that would otherwise go unobserved. Lastly, all the pyramids and causeways in the study site, along with ancient harbors and valley temples, as indicators of preexisting river channels, were digitized from satellite data and available archeological resources and overlaid onto the delineated Ahramat Branch for geospatial analysis.

Geophysical survey and sediment coring

Geophysical measurements using Ground Penetrating Radar (GPR) and Electromagnetic Tomography (EMT) were utilized to map subsurface fluvial features and validate the satellite remote sensing findings. GPR is effective in detecting changes of dielectric constant properties of sediment layers, and its signal responses can be directly related to changes in relative porosity, material composition, and moisture content. Therefore, GPR can help in identifying transitional boundaries in subsurface layers. EMT, on the other hand, shows the variations and thickness of large-scale sedimentary deposits and is more useful in clay-rich soil than GPR. In summer 2022, a geophysical profile was measured using GPR and EMT units with a total length of approximately 1.2 km. The GPR survey was conducted with a central frequency antenna of 35 MHz and a trigger interval of 5 cm. The EMT survey was performed using the multi-frequency terrain conductivity (EM–34–3) measuring system with a spacing of 10–11 meters between stations. To validate the remote sensing and geophysical data, two sediment cores with depths of 20 m (Core A) and 13 m (Core B) were collected using a deep soil driller. These cores were collected from along the geophysical profile in the floodplain. Sieving and organic analysis were performed on the sediment samples at Tanta University sediment lab to extract information about grain size for soil texture and total organic carbon. In soil texture analysis medium to coarse sediment, such as sands, are typical for river channel sediments, loamy sand and sandy loam deposits can be interpreted as levees and crevasse splays, whereas fine texture deposits, such as silt loam, silty clay loam, and clay deposits, are representative of the more distal parts of the river floodplain 47 .

Data availability

Data for replicating the results of this study are available as supplementary files at: https://figshare.com/articles/journal_contribution/Pyramids_Elevations_and_Distances_xlsx/25216259 .

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Acknowledgements

This work was funded by NSF grant # 2114295 awarded to E.G., S.O. and T.R. and partially supported by Research Momentum Fund, UNCW, to E.G. TanDEM-X data was awarded to E.G. and R.E by the German Aerospace Centre (DLR) (contract # DEM_OTHER2886). Permissions for collecting soil coring and sampling were obtained from the Faculty of Science, Tanta University, Egypt by coauthors Dr. Amr Fhail and Dr. Mohamed Fathy. Bradley Graves at Macquarie University assisted with preparation of the sedimentological figures. Hamada Salama at NRIAG assisted with the GPR field data collection.

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Eman Ghoneim

School of Natural Sciences, Macquarie University, Macquarie, NSW, 2109, Australia

Timothy J. Ralph

Department of History, The University of Memphis, Memphis, TN, 38152-3450, USA

Suzanne Onstine

Near Eastern Languages and Civilizations, University of Chicago, Chicago, IL, 60637, USA

Raghda El-Behaedi

National Research Institute of Astronomy and Geophysics (NRIAG), Helwan, Cairo, 11421, Egypt

Gad El-Qady, Mahfooz Hafez, Magdy Atya, Mohamed Ebrahim & Ashraf Khozym

Geology Department, Faculty of Science, Tanta University, Tanta, 31527, Egypt

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Eman Ghoneim conceived the ideas, lead the research project, and conducted the data processing and interpretations. The manuscript was written and prepared by Eman Ghoneim. Timothy J. Ralph co-supervised the project, contributed to the geomorphological and sedimentological interpretations, edited the manuscript and the figures. Suzanne Onstine co-supervised the project, contributed to the archeological and historical interpretations, and edited the manuscript. Raghda El-Behaedi contributed to the remote sensing data processing and methodology and edited the manuscript. Gad El-Qady supervised the geophysical survey. Mahfooz Hafez, Magdy Atya, Mohamed Ebrahim, Ashraf Khozym designed, collected, and interpreted the GPR and EMT data. Amr S. Fahil and Mohamed S. Fathy supervised the soil coring, sediment analysis, drafted sedimentological figures and contributed to the interpretations. All authors reviewed the manuscript and participated in the fieldwork.

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Ghoneim, E., Ralph, T.J., Onstine, S. et al. The Egyptian pyramid chain was built along the now abandoned Ahramat Nile Branch. Commun Earth Environ 5 , 233 (2024). https://doi.org/10.1038/s43247-024-01379-7

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Diet Review: MIND Diet

Finding yourself confused by the seemingly endless promotion of weight-loss strategies and diet plans?  In this series , we take a look at some popular diets—and review the research behind them.

What Is It?

The Mediterranean-DASH Diet Intervention for Neurodegenerative Delay, or MIND diet, targets the health of the aging brain. Dementia is the sixth leading cause of death in the United States, driving many people to search for ways to prevent cognitive decline. In 2015, Dr. Martha Clare Morris and colleagues at Rush University Medical Center and the Harvard Chan School of Public Health published two papers introducing the MIND diet. [1,2] Both the Mediterranean and DASH diets had already been associated with preservation of cognitive function, presumably through their protective effects against cardiovascular disease, which in turn preserved brain health.

The research team followed a group of older adults for up to 10 years from the Rush Memory and Aging Project (MAP), a study of residents free of dementia at the time of enrollment. They were recruited from more than 40 retirement communities and senior public housing units in the Chicago area. More than 1,000 participants filled out annual dietary questionnaires for nine years and had two cognitive assessments. A MIND diet score was developed to identify foods and nutrients, along with daily serving sizes, related to protection against dementia and cognitive decline. The results of the study produced fifteen dietary components that were classified as either “brain healthy” or as unhealthy. Participants with the highest MIND diet scores had a significantly slower rate of cognitive decline compared with those with the lowest scores. [1] The effects of the MIND diet on cognition showed greater effects than either the Mediterranean or the DASH diet alone.

How It Works

The purpose of the research was to see if the MIND diet, partially based on the Mediterranean and DASH diets, could directly prevent the onset or slow the progression of dementia. All three diets highlight plant-based foods and limit the intake of animal and high saturated fat foods. The MIND diet recommends specific “brain healthy” foods to include, and five unhealthy food items to limit. [1]

The healthy items the MIND diet guidelines* suggest include:

• 3+ servings a day of whole grains
• 1+ servings a day of vegetables (other than green leafy)
• 6+ servings a week of green leafy vegetables
• 5+ servings a week of nuts
• 4+ meals a week of beans
• 2+ servings a week of berries
• 2+ meals a week of poultry
• 1+ meals a week of fish
• Mainly olive oil if added fat is used

The unhealthy items, which are higher in saturated and trans fat , include:

• Less than 5 servings a week of pastries and sweets
• Less than 4 servings a week of red meat (including beef, pork, lamb, and products made from these meats)
• Less than one serving a week of  cheese and fried foods
• Less than 1 tablespoon a day of butter/stick margarine

*Note: modest variations in amounts of these foods have been used in subsequent studies. [9,10]

This sample meal plan is roughly 2000 calories, the recommended intake for an average person. If you have higher calorie needs, you may add an additional snack or two; if you have lower calorie needs, you may remove a snack. If you have more specific nutritional needs or would like assistance in creating additional meal plans, consult with a registered dietitian. 

Breakfast: 1 cup cooked steel-cut oats mixed with 2 tablespoons slivered almonds, ¾ cup fresh or frozen blueberries, sprinkle of cinnamon

Snack: 1 medium orange

• Beans and rice – In medium pot, heat 1 tbsp olive oil. Add and sauté ½ chopped onion, 1 tsp cumin, and 1 tsp garlic powder until onion is softened. Mix in 1 cup canned beans, drained and rinsed. Serve bean mixture over 1 cup cooked brown rice.
• 2 cups salad (e.g., mixed greens, cucumbers, bell peppers) with dressing (mix together 2 tbsp olive oil, 1 tbsp lemon juice or vinegar, ½ teaspoon Dijon mustard, ½ teaspoon garlic powder, ¼ tsp black pepper)

Snack: ¼ cup unsalted mixed nuts

• 3 ounces baked salmon brushed with same salad dressing used at lunch
• 1 cup chopped steamed cauliflower
• 1 whole grain roll dipped in 1 tbsp olive oil

Is alcohol part of the MIND diet?

Wine was included as one of the 15 original dietary components in the MIND diet score, in which a moderate amount was found to be associated with cognitive health. [1] However, in subsequent MIND trials it was omitted for “safety” reasons. The effect of alcohol on an individual is complex, so that blanket recommendations about alcohol are not possible. Based on one’s unique personal and family history, alcohol offers each person a different spectrum of benefits and risks. Whether or not to include alcohol is a personal decision that should be discussed with your healthcare provider. For more information, read Alcohol: Balancing Risks and Benefits .

The Research So Far

The MIND diet contains foods rich in certain vitamins, carotenoids, and flavonoids that are believed to protect the brain by reducing oxidative stress and inflammation. Although the aim of the MIND diet is on brain health, it may also benefit heart health, diabetes, and certain cancers because it includes components of the  Mediterranean  and  DASH  diets, which have been shown to lower the risk of these diseases.

Cohort studies

Researchers found a 53% lower rate of Alzheimer’s disease for those with the highest MIND diet scores (indicating a higher intake of foods on the MIND diet). Even those participants who had moderate MIND diet scores showed a 35% lower rate compared with those with the lowest MIND scores. [2] The results didn’t change after adjusting for factors associated with dementia including healthy lifestyle behaviors, cardiovascular-related conditions (e.g., high blood pressure, stroke, diabetes), depression, and obesity, supporting the conclusion that the MIND diet was associated with the preservation of cognitive function.

Several other large cohort studies have shown that participants with higher MIND diet scores, compared with those with the lowest scores, had better cognitive functioning, larger total brain volume, higher memory scores, lower risk of dementia, and slower cognitive decline, even when including participants with Alzheimer’s disease and history of stroke. [3-8]

Clinical trials

A 2023 randomized controlled trial followed 604 adults aged 65 and older who at baseline were overweight (BMI greater than 25), ate a suboptimal diet, and did not have cognitive impairment but had a first-degree relative with dementia. [9] The intervention group was taught to follow a MIND diet, and the control group continued to consume their usual diet. Both groups were guided throughout the study by registered dietitians to follow their assigned diet and reduce their intake by 250 calories a day. The authors found that participants in both the MIND and control groups showed improved cognitive performance. Both groups also lost about 11 pounds, but the MIND diet group showed greater improvements in diet quality score. The authors examined changes in the brain using magnetic resonance imaging, but findings did not differ between groups. [10] Nutrition experts commenting on this study noted that both groups lost a similar amount of weight, as intended, but the control group likely improved their diet quality as well (they had been coached to eat their usual foods but were taught goal setting, calorie tracking, and mindful eating techniques), which could have prevented significant changes from being seen between groups. Furthermore, the duration of the study–3 years–may have been too short to show significant improvement in cognitive function.

The results of this study showed that the MIND diet does not slow cognitive aging over a 3-year treatment period. Whether the MIND diet or other diets can slow cognitive aging over longer time periods remains a topic of intense interest.

Other factors

Research has found that greater poverty and less education are strongly associated with lower MIND diet scores and lower cognitive function. [11]

Potential Pitfalls

• The MIND diet is flexible in that it does not include rigid meal plans. However, this also means that people will need to create their own meal plans and recipes based on the foods recommended on the MIND diet. This may be challenging for those who do not cook. Those who eat out frequently may need to spend time reviewing restaurant menus.
• Although the diet plan specifies daily and weekly amounts of foods to include and not include, it does not restrict the diet to eating only these foods. It also does not provide meal plans or emphasize portion sizes or exercise .

Bottom Line  

The MIND diet can be a healthful eating plan that incorporates dietary patterns from the Mediterranean and DASH , both of which have suggested benefits in preventing and improving cardiovascular disease and diabetes , and supporting healthy aging. When used in conjunction with a balanced plate guide , the diet may also promote healthy weight loss if desired. Whether or not following the MIND diet can slow cognitive aging over longer time periods remains an area of interest, and more research needs to be done to extend the MIND studies in other populations.

• Healthy Weight
• The Best Diet: Quality Counts
• Healthy Dietary Styles
• Other Diet Reviews
• Morris MC, Tangney CC, Wang Y, Sacks FM, Barnes LL, Bennett DA, Aggarwal NT. MIND diet slows cognitive decline with aging. Alzheimer’s & dementia . 2015 Sep 1;11(9):1015-22.
• Morris MC, Tangney CC, Wang Y, Sacks FM, Bennett DA, Aggarwal NT. MIND diet associated with reduced incidence of Alzheimer’s disease. Alzheimer’s & Dementia . 2015 Sep 1;11(9):1007-14.
• Dhana K, James BD, Agarwal P, Aggarwal NT, Cherian LJ, Leurgans SE, Barnes LL, Bennett DA, Schneider JA. MIND diet, common brain pathologies, and cognition in community-dwelling older adults. Journal of Alzheimer’s Disease . 2021 Jan 1;83(2):683-92.
• Cherian L, Wang Y, Fakuda K, Leurgans S, Aggarwal N, Morris M. Mediterranean-Dash Intervention for Neurodegenerative Delay (MIND) diet slows cognitive decline after stroke. The journal of prevention of Alzheimer’s disease . 2019 Oct;6(4):267-73.
• Hosking DE, Eramudugolla R, Cherbuin N, Anstey KJ. MIND not Mediterranean diet related to 12-year incidence of cognitive impairment in an Australian longitudinal cohort study. Alzheimer’s & Dementia . 2019 Apr 1;15(4):581-9.
• Melo van Lent D, O’Donnell A, Beiser AS, Vasan RS, DeCarli CS, Scarmeas N, Wagner M, Jacques PF, Seshadri S, Himali JJ, Pase MP. Mind diet adherence and cognitive performance in the Framingham heart study. Journal of Alzheimer’s Disease . 2021 Jan 1;82(2):827-39.
• Berendsen AM, Kang JH, Feskens EJ, de Groot CP, Grodstein F, van de Rest O. Association of long-term adherence to the mind diet with cognitive function and cognitive decline in American women. The journal of nutrition, health & aging . 2018 Feb;22(2):222-9. Disclosure: Grodstein reports grants from International Nut Council, other from California Walnut Council, outside the submitted work.
• Chen H, Dhana K, Huang Y, Huang L, Tao Y, Liu X, van Lent DM, Zheng Y, Ascherio A, Willett W, Yuan C. Association of the Mediterranean Dietary Approaches to Stop Hypertension Intervention for Neurodegenerative Delay (MIND) Diet With the Risk of Dementia. JAMA psychiatry . 2023 May 3.
• Liu X, Morris MC, Dhana K, Ventrelle J, Johnson K, Bishop L, Hollings CS, Boulin A, Laranjo N, Stubbs BJ, Reilly X. Mediterranean-DASH Intervention for Neurodegenerative Delay (MIND) study: rationale, design and baseline characteristics of a randomized control trial of the MIND diet on cognitive decline. Contemporary clinical trials . 2021 Mar 1;102:106270. Disclosure: several corporations generously donated mixed nuts (International Tree Nut Council Nutrition Research and Education Foundation), peanut butter (The Peanut Institute), extra virgin olive oil (Innoliva-ADM Capital Europe LLP), and blueberries (U.S. Highbush Blueberry Council). These items will be distributed to those participants who are randomized to the MIND diet arm.
• Barnes LL, Dhana K, Liu X, Carey VJ, Ventrelle J, Johnson K, Hollings CS, Bishop L, Laranjo N, Stubbs BJ, Reilly X. Trial of the MIND Diet for Prevention of Cognitive Decline in Older Persons. New England Journal of Medicine . 2023 Jul 18.
• Boumenna T, Scott TM, Lee JS, Zhang X, Kriebel D, Tucker KL, Palacios N. MIND diet and cognitive function in Puerto Rican older adults. The Journals of Gerontology: Series A . 2022 Mar;77(3):605-13.

Last reviewed August 2023

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