literature review software development methods

Approaches in Determining Software Development Methods for Organizations: A Systematic Literature Review

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NCBI Bookshelf. A service of the National Library of Medicine, National Institutes of Health.

Lau F, Kuziemsky C, editors. Handbook of eHealth Evaluation: An Evidence-based Approach [Internet]. Victoria (BC): University of Victoria; 2017 Feb 27.

Handbook of eHealth Evaluation: An Evidence-based Approach [Internet].

Chapter 9 methods for literature reviews.

Guy Paré and Spyros Kitsiou .

9.1. Introduction

Literature reviews play a critical role in scholarship because science remains, first and foremost, a cumulative endeavour ( vom Brocke et al., 2009 ). As in any academic discipline, rigorous knowledge syntheses are becoming indispensable in keeping up with an exponentially growing eHealth literature, assisting practitioners, academics, and graduate students in finding, evaluating, and synthesizing the contents of many empirical and conceptual papers. Among other methods, literature reviews are essential for: (a) identifying what has been written on a subject or topic; (b) determining the extent to which a specific research area reveals any interpretable trends or patterns; (c) aggregating empirical findings related to a narrow research question to support evidence-based practice; (d) generating new frameworks and theories; and (e) identifying topics or questions requiring more investigation ( Paré, Trudel, Jaana, & Kitsiou, 2015 ).

Literature reviews can take two major forms. The most prevalent one is the “literature review” or “background” section within a journal paper or a chapter in a graduate thesis. This section synthesizes the extant literature and usually identifies the gaps in knowledge that the empirical study addresses ( Sylvester, Tate, & Johnstone, 2013 ). It may also provide a theoretical foundation for the proposed study, substantiate the presence of the research problem, justify the research as one that contributes something new to the cumulated knowledge, or validate the methods and approaches for the proposed study ( Hart, 1998 ; Levy & Ellis, 2006 ).

The second form of literature review, which is the focus of this chapter, constitutes an original and valuable work of research in and of itself ( Paré et al., 2015 ). Rather than providing a base for a researcher’s own work, it creates a solid starting point for all members of the community interested in a particular area or topic ( Mulrow, 1987 ). The so-called “review article” is a journal-length paper which has an overarching purpose to synthesize the literature in a field, without collecting or analyzing any primary data ( Green, Johnson, & Adams, 2006 ).

When appropriately conducted, review articles represent powerful information sources for practitioners looking for state-of-the art evidence to guide their decision-making and work practices ( Paré et al., 2015 ). Further, high-quality reviews become frequently cited pieces of work which researchers seek out as a first clear outline of the literature when undertaking empirical studies ( Cooper, 1988 ; Rowe, 2014 ). Scholars who track and gauge the impact of articles have found that review papers are cited and downloaded more often than any other type of published article ( Cronin, Ryan, & Coughlan, 2008 ; Montori, Wilczynski, Morgan, Haynes, & Hedges, 2003 ; Patsopoulos, Analatos, & Ioannidis, 2005 ). The reason for their popularity may be the fact that reading the review enables one to have an overview, if not a detailed knowledge of the area in question, as well as references to the most useful primary sources ( Cronin et al., 2008 ). Although they are not easy to conduct, the commitment to complete a review article provides a tremendous service to one’s academic community ( Paré et al., 2015 ; Petticrew & Roberts, 2006 ). Most, if not all, peer-reviewed journals in the fields of medical informatics publish review articles of some type.

The main objectives of this chapter are fourfold: (a) to provide an overview of the major steps and activities involved in conducting a stand-alone literature review; (b) to describe and contrast the different types of review articles that can contribute to the eHealth knowledge base; (c) to illustrate each review type with one or two examples from the eHealth literature; and (d) to provide a series of recommendations for prospective authors of review articles in this domain.

9.2. Overview of the Literature Review Process and Steps

As explained in Templier and Paré (2015) , there are six generic steps involved in conducting a review article:

• formulating the research question(s) and objective(s),
• searching the extant literature,
• screening for inclusion,
• assessing the quality of primary studies,
• extracting data, and
• analyzing data.

Although these steps are presented here in sequential order, one must keep in mind that the review process can be iterative and that many activities can be initiated during the planning stage and later refined during subsequent phases ( Finfgeld-Connett & Johnson, 2013 ; Kitchenham & Charters, 2007 ).

Formulating the research question(s) and objective(s): As a first step, members of the review team must appropriately justify the need for the review itself ( Petticrew & Roberts, 2006 ), identify the review’s main objective(s) ( Okoli & Schabram, 2010 ), and define the concepts or variables at the heart of their synthesis ( Cooper & Hedges, 2009 ; Webster & Watson, 2002 ). Importantly, they also need to articulate the research question(s) they propose to investigate ( Kitchenham & Charters, 2007 ). In this regard, we concur with Jesson, Matheson, and Lacey (2011) that clearly articulated research questions are key ingredients that guide the entire review methodology; they underscore the type of information that is needed, inform the search for and selection of relevant literature, and guide or orient the subsequent analysis. Searching the extant literature: The next step consists of searching the literature and making decisions about the suitability of material to be considered in the review ( Cooper, 1988 ). There exist three main coverage strategies. First, exhaustive coverage means an effort is made to be as comprehensive as possible in order to ensure that all relevant studies, published and unpublished, are included in the review and, thus, conclusions are based on this all-inclusive knowledge base. The second type of coverage consists of presenting materials that are representative of most other works in a given field or area. Often authors who adopt this strategy will search for relevant articles in a small number of top-tier journals in a field ( Paré et al., 2015 ). In the third strategy, the review team concentrates on prior works that have been central or pivotal to a particular topic. This may include empirical studies or conceptual papers that initiated a line of investigation, changed how problems or questions were framed, introduced new methods or concepts, or engendered important debate ( Cooper, 1988 ). Screening for inclusion: The following step consists of evaluating the applicability of the material identified in the preceding step ( Levy & Ellis, 2006 ; vom Brocke et al., 2009 ). Once a group of potential studies has been identified, members of the review team must screen them to determine their relevance ( Petticrew & Roberts, 2006 ). A set of predetermined rules provides a basis for including or excluding certain studies. This exercise requires a significant investment on the part of researchers, who must ensure enhanced objectivity and avoid biases or mistakes. As discussed later in this chapter, for certain types of reviews there must be at least two independent reviewers involved in the screening process and a procedure to resolve disagreements must also be in place ( Liberati et al., 2009 ; Shea et al., 2009 ). Assessing the quality of primary studies: In addition to screening material for inclusion, members of the review team may need to assess the scientific quality of the selected studies, that is, appraise the rigour of the research design and methods. Such formal assessment, which is usually conducted independently by at least two coders, helps members of the review team refine which studies to include in the final sample, determine whether or not the differences in quality may affect their conclusions, or guide how they analyze the data and interpret the findings ( Petticrew & Roberts, 2006 ). Ascribing quality scores to each primary study or considering through domain-based evaluations which study components have or have not been designed and executed appropriately makes it possible to reflect on the extent to which the selected study addresses possible biases and maximizes validity ( Shea et al., 2009 ). Extracting data: The following step involves gathering or extracting applicable information from each primary study included in the sample and deciding what is relevant to the problem of interest ( Cooper & Hedges, 2009 ). Indeed, the type of data that should be recorded mainly depends on the initial research questions ( Okoli & Schabram, 2010 ). However, important information may also be gathered about how, when, where and by whom the primary study was conducted, the research design and methods, or qualitative/quantitative results ( Cooper & Hedges, 2009 ). Analyzing and synthesizing data : As a final step, members of the review team must collate, summarize, aggregate, organize, and compare the evidence extracted from the included studies. The extracted data must be presented in a meaningful way that suggests a new contribution to the extant literature ( Jesson et al., 2011 ). Webster and Watson (2002) warn researchers that literature reviews should be much more than lists of papers and should provide a coherent lens to make sense of extant knowledge on a given topic. There exist several methods and techniques for synthesizing quantitative (e.g., frequency analysis, meta-analysis) and qualitative (e.g., grounded theory, narrative analysis, meta-ethnography) evidence ( Dixon-Woods, Agarwal, Jones, Young, & Sutton, 2005 ; Thomas & Harden, 2008 ).

9.3. Types of Review Articles and Brief Illustrations

EHealth researchers have at their disposal a number of approaches and methods for making sense out of existing literature, all with the purpose of casting current research findings into historical contexts or explaining contradictions that might exist among a set of primary research studies conducted on a particular topic. Our classification scheme is largely inspired from Paré and colleagues’ (2015) typology. Below we present and illustrate those review types that we feel are central to the growth and development of the eHealth domain.

9.3.1. Narrative Reviews

The narrative review is the “traditional” way of reviewing the extant literature and is skewed towards a qualitative interpretation of prior knowledge ( Sylvester et al., 2013 ). Put simply, a narrative review attempts to summarize or synthesize what has been written on a particular topic but does not seek generalization or cumulative knowledge from what is reviewed ( Davies, 2000 ; Green et al., 2006 ). Instead, the review team often undertakes the task of accumulating and synthesizing the literature to demonstrate the value of a particular point of view ( Baumeister & Leary, 1997 ). As such, reviewers may selectively ignore or limit the attention paid to certain studies in order to make a point. In this rather unsystematic approach, the selection of information from primary articles is subjective, lacks explicit criteria for inclusion and can lead to biased interpretations or inferences ( Green et al., 2006 ). There are several narrative reviews in the particular eHealth domain, as in all fields, which follow such an unstructured approach ( Silva et al., 2015 ; Paul et al., 2015 ).

Despite these criticisms, this type of review can be very useful in gathering together a volume of literature in a specific subject area and synthesizing it. As mentioned above, its primary purpose is to provide the reader with a comprehensive background for understanding current knowledge and highlighting the significance of new research ( Cronin et al., 2008 ). Faculty like to use narrative reviews in the classroom because they are often more up to date than textbooks, provide a single source for students to reference, and expose students to peer-reviewed literature ( Green et al., 2006 ). For researchers, narrative reviews can inspire research ideas by identifying gaps or inconsistencies in a body of knowledge, thus helping researchers to determine research questions or formulate hypotheses. Importantly, narrative reviews can also be used as educational articles to bring practitioners up to date with certain topics of issues ( Green et al., 2006 ).

Recently, there have been several efforts to introduce more rigour in narrative reviews that will elucidate common pitfalls and bring changes into their publication standards. Information systems researchers, among others, have contributed to advancing knowledge on how to structure a “traditional” review. For instance, Levy and Ellis (2006) proposed a generic framework for conducting such reviews. Their model follows the systematic data processing approach comprised of three steps, namely: (a) literature search and screening; (b) data extraction and analysis; and (c) writing the literature review. They provide detailed and very helpful instructions on how to conduct each step of the review process. As another methodological contribution, vom Brocke et al. (2009) offered a series of guidelines for conducting literature reviews, with a particular focus on how to search and extract the relevant body of knowledge. Last, Bandara, Miskon, and Fielt (2011) proposed a structured, predefined and tool-supported method to identify primary studies within a feasible scope, extract relevant content from identified articles, synthesize and analyze the findings, and effectively write and present the results of the literature review. We highly recommend that prospective authors of narrative reviews consult these useful sources before embarking on their work.

Darlow and Wen (2015) provide a good example of a highly structured narrative review in the eHealth field. These authors synthesized published articles that describe the development process of mobile health ( m-health ) interventions for patients’ cancer care self-management. As in most narrative reviews, the scope of the research questions being investigated is broad: (a) how development of these systems are carried out; (b) which methods are used to investigate these systems; and (c) what conclusions can be drawn as a result of the development of these systems. To provide clear answers to these questions, a literature search was conducted on six electronic databases and Google Scholar . The search was performed using several terms and free text words, combining them in an appropriate manner. Four inclusion and three exclusion criteria were utilized during the screening process. Both authors independently reviewed each of the identified articles to determine eligibility and extract study information. A flow diagram shows the number of studies identified, screened, and included or excluded at each stage of study selection. In terms of contributions, this review provides a series of practical recommendations for m-health intervention development.

9.3.2. Descriptive or Mapping Reviews

The primary goal of a descriptive review is to determine the extent to which a body of knowledge in a particular research topic reveals any interpretable pattern or trend with respect to pre-existing propositions, theories, methodologies or findings ( King & He, 2005 ; Paré et al., 2015 ). In contrast with narrative reviews, descriptive reviews follow a systematic and transparent procedure, including searching, screening and classifying studies ( Petersen, Vakkalanka, & Kuzniarz, 2015 ). Indeed, structured search methods are used to form a representative sample of a larger group of published works ( Paré et al., 2015 ). Further, authors of descriptive reviews extract from each study certain characteristics of interest, such as publication year, research methods, data collection techniques, and direction or strength of research outcomes (e.g., positive, negative, or non-significant) in the form of frequency analysis to produce quantitative results ( Sylvester et al., 2013 ). In essence, each study included in a descriptive review is treated as the unit of analysis and the published literature as a whole provides a database from which the authors attempt to identify any interpretable trends or draw overall conclusions about the merits of existing conceptualizations, propositions, methods or findings ( Paré et al., 2015 ). In doing so, a descriptive review may claim that its findings represent the state of the art in a particular domain ( King & He, 2005 ).

In the fields of health sciences and medical informatics, reviews that focus on examining the range, nature and evolution of a topic area are described by Anderson, Allen, Peckham, and Goodwin (2008) as mapping reviews . Like descriptive reviews, the research questions are generic and usually relate to publication patterns and trends. There is no preconceived plan to systematically review all of the literature although this can be done. Instead, researchers often present studies that are representative of most works published in a particular area and they consider a specific time frame to be mapped.

An example of this approach in the eHealth domain is offered by DeShazo, Lavallie, and Wolf (2009). The purpose of this descriptive or mapping review was to characterize publication trends in the medical informatics literature over a 20-year period (1987 to 2006). To achieve this ambitious objective, the authors performed a bibliometric analysis of medical informatics citations indexed in medline using publication trends, journal frequencies, impact factors, Medical Subject Headings (MeSH) term frequencies, and characteristics of citations. Findings revealed that there were over 77,000 medical informatics articles published during the covered period in numerous journals and that the average annual growth rate was 12%. The MeSH term analysis also suggested a strong interdisciplinary trend. Finally, average impact scores increased over time with two notable growth periods. Overall, patterns in research outputs that seem to characterize the historic trends and current components of the field of medical informatics suggest it may be a maturing discipline (DeShazo et al., 2009).

9.3.3. Scoping Reviews

Scoping reviews attempt to provide an initial indication of the potential size and nature of the extant literature on an emergent topic (Arksey & O’Malley, 2005; Daudt, van Mossel, & Scott, 2013 ; Levac, Colquhoun, & O’Brien, 2010). A scoping review may be conducted to examine the extent, range and nature of research activities in a particular area, determine the value of undertaking a full systematic review (discussed next), or identify research gaps in the extant literature ( Paré et al., 2015 ). In line with their main objective, scoping reviews usually conclude with the presentation of a detailed research agenda for future works along with potential implications for both practice and research.

Unlike narrative and descriptive reviews, the whole point of scoping the field is to be as comprehensive as possible, including grey literature (Arksey & O’Malley, 2005). Inclusion and exclusion criteria must be established to help researchers eliminate studies that are not aligned with the research questions. It is also recommended that at least two independent coders review abstracts yielded from the search strategy and then the full articles for study selection ( Daudt et al., 2013 ). The synthesized evidence from content or thematic analysis is relatively easy to present in tabular form (Arksey & O’Malley, 2005; Thomas & Harden, 2008 ).

One of the most highly cited scoping reviews in the eHealth domain was published by Archer, Fevrier-Thomas, Lokker, McKibbon, and Straus (2011) . These authors reviewed the existing literature on personal health record ( phr ) systems including design, functionality, implementation, applications, outcomes, and benefits. Seven databases were searched from 1985 to March 2010. Several search terms relating to phr s were used during this process. Two authors independently screened titles and abstracts to determine inclusion status. A second screen of full-text articles, again by two independent members of the research team, ensured that the studies described phr s. All in all, 130 articles met the criteria and their data were extracted manually into a database. The authors concluded that although there is a large amount of survey, observational, cohort/panel, and anecdotal evidence of phr benefits and satisfaction for patients, more research is needed to evaluate the results of phr implementations. Their in-depth analysis of the literature signalled that there is little solid evidence from randomized controlled trials or other studies through the use of phr s. Hence, they suggested that more research is needed that addresses the current lack of understanding of optimal functionality and usability of these systems, and how they can play a beneficial role in supporting patient self-management ( Archer et al., 2011 ).

9.3.4. Forms of Aggregative Reviews

Healthcare providers, practitioners, and policy-makers are nowadays overwhelmed with large volumes of information, including research-based evidence from numerous clinical trials and evaluation studies, assessing the effectiveness of health information technologies and interventions ( Ammenwerth & de Keizer, 2004 ; Deshazo et al., 2009 ). It is unrealistic to expect that all these disparate actors will have the time, skills, and necessary resources to identify the available evidence in the area of their expertise and consider it when making decisions. Systematic reviews that involve the rigorous application of scientific strategies aimed at limiting subjectivity and bias (i.e., systematic and random errors) can respond to this challenge.

Systematic reviews attempt to aggregate, appraise, and synthesize in a single source all empirical evidence that meet a set of previously specified eligibility criteria in order to answer a clearly formulated and often narrow research question on a particular topic of interest to support evidence-based practice ( Liberati et al., 2009 ). They adhere closely to explicit scientific principles ( Liberati et al., 2009 ) and rigorous methodological guidelines (Higgins & Green, 2008) aimed at reducing random and systematic errors that can lead to deviations from the truth in results or inferences. The use of explicit methods allows systematic reviews to aggregate a large body of research evidence, assess whether effects or relationships are in the same direction and of the same general magnitude, explain possible inconsistencies between study results, and determine the strength of the overall evidence for every outcome of interest based on the quality of included studies and the general consistency among them ( Cook, Mulrow, & Haynes, 1997 ). The main procedures of a systematic review involve:

• Formulating a review question and developing a search strategy based on explicit inclusion criteria for the identification of eligible studies (usually described in the context of a detailed review protocol).
• Searching for eligible studies using multiple databases and information sources, including grey literature sources, without any language restrictions.
• Selecting studies, extracting data, and assessing risk of bias in a duplicate manner using two independent reviewers to avoid random or systematic errors in the process.
• Analyzing data using quantitative or qualitative methods.
• Presenting results in summary of findings tables.
• Interpreting results and drawing conclusions.

Many systematic reviews, but not all, use statistical methods to combine the results of independent studies into a single quantitative estimate or summary effect size. Known as meta-analyses , these reviews use specific data extraction and statistical techniques (e.g., network, frequentist, or Bayesian meta-analyses) to calculate from each study by outcome of interest an effect size along with a confidence interval that reflects the degree of uncertainty behind the point estimate of effect ( Borenstein, Hedges, Higgins, & Rothstein, 2009 ; Deeks, Higgins, & Altman, 2008 ). Subsequently, they use fixed or random-effects analysis models to combine the results of the included studies, assess statistical heterogeneity, and calculate a weighted average of the effect estimates from the different studies, taking into account their sample sizes. The summary effect size is a value that reflects the average magnitude of the intervention effect for a particular outcome of interest or, more generally, the strength of a relationship between two variables across all studies included in the systematic review. By statistically combining data from multiple studies, meta-analyses can create more precise and reliable estimates of intervention effects than those derived from individual studies alone, when these are examined independently as discrete sources of information.

The review by Gurol-Urganci, de Jongh, Vodopivec-Jamsek, Atun, and Car (2013) on the effects of mobile phone messaging reminders for attendance at healthcare appointments is an illustrative example of a high-quality systematic review with meta-analysis. Missed appointments are a major cause of inefficiency in healthcare delivery with substantial monetary costs to health systems. These authors sought to assess whether mobile phone-based appointment reminders delivered through Short Message Service ( sms ) or Multimedia Messaging Service ( mms ) are effective in improving rates of patient attendance and reducing overall costs. To this end, they conducted a comprehensive search on multiple databases using highly sensitive search strategies without language or publication-type restrictions to identify all rct s that are eligible for inclusion. In order to minimize the risk of omitting eligible studies not captured by the original search, they supplemented all electronic searches with manual screening of trial registers and references contained in the included studies. Study selection, data extraction, and risk of bias assessments were performed inde­­pen­dently by two coders using standardized methods to ensure consistency and to eliminate potential errors. Findings from eight rct s involving 6,615 participants were pooled into meta-analyses to calculate the magnitude of effects that mobile text message reminders have on the rate of attendance at healthcare appointments compared to no reminders and phone call reminders.

Meta-analyses are regarded as powerful tools for deriving meaningful conclusions. However, there are situations in which it is neither reasonable nor appropriate to pool studies together using meta-analytic methods simply because there is extensive clinical heterogeneity between the included studies or variation in measurement tools, comparisons, or outcomes of interest. In these cases, systematic reviews can use qualitative synthesis methods such as vote counting, content analysis, classification schemes and tabulations, as an alternative approach to narratively synthesize the results of the independent studies included in the review. This form of review is known as qualitative systematic review.

A rigorous example of one such review in the eHealth domain is presented by Mickan, Atherton, Roberts, Heneghan, and Tilson (2014) on the use of handheld computers by healthcare professionals and their impact on access to information and clinical decision-making. In line with the methodological guide­lines for systematic reviews, these authors: (a) developed and registered with prospero ( www.crd.york.ac.uk/ prospero / ) an a priori review protocol; (b) conducted comprehensive searches for eligible studies using multiple databases and other supplementary strategies (e.g., forward searches); and (c) subsequently carried out study selection, data extraction, and risk of bias assessments in a duplicate manner to eliminate potential errors in the review process. Heterogeneity between the included studies in terms of reported outcomes and measures precluded the use of meta-analytic methods. To this end, the authors resorted to using narrative analysis and synthesis to describe the effectiveness of handheld computers on accessing information for clinical knowledge, adherence to safety and clinical quality guidelines, and diagnostic decision-making.

In recent years, the number of systematic reviews in the field of health informatics has increased considerably. Systematic reviews with discordant findings can cause great confusion and make it difficult for decision-makers to interpret the review-level evidence ( Moher, 2013 ). Therefore, there is a growing need for appraisal and synthesis of prior systematic reviews to ensure that decision-making is constantly informed by the best available accumulated evidence. Umbrella reviews , also known as overviews of systematic reviews, are tertiary types of evidence synthesis that aim to accomplish this; that is, they aim to compare and contrast findings from multiple systematic reviews and meta-analyses ( Becker & Oxman, 2008 ). Umbrella reviews generally adhere to the same principles and rigorous methodological guidelines used in systematic reviews. However, the unit of analysis in umbrella reviews is the systematic review rather than the primary study ( Becker & Oxman, 2008 ). Unlike systematic reviews that have a narrow focus of inquiry, umbrella reviews focus on broader research topics for which there are several potential interventions ( Smith, Devane, Begley, & Clarke, 2011 ). A recent umbrella review on the effects of home telemonitoring interventions for patients with heart failure critically appraised, compared, and synthesized evidence from 15 systematic reviews to investigate which types of home telemonitoring technologies and forms of interventions are more effective in reducing mortality and hospital admissions ( Kitsiou, Paré, & Jaana, 2015 ).

9.3.5. Realist Reviews

Realist reviews are theory-driven interpretative reviews developed to inform, enhance, or supplement conventional systematic reviews by making sense of heterogeneous evidence about complex interventions applied in diverse contexts in a way that informs policy decision-making ( Greenhalgh, Wong, Westhorp, & Pawson, 2011 ). They originated from criticisms of positivist systematic reviews which centre on their “simplistic” underlying assumptions ( Oates, 2011 ). As explained above, systematic reviews seek to identify causation. Such logic is appropriate for fields like medicine and education where findings of randomized controlled trials can be aggregated to see whether a new treatment or intervention does improve outcomes. However, many argue that it is not possible to establish such direct causal links between interventions and outcomes in fields such as social policy, management, and information systems where for any intervention there is unlikely to be a regular or consistent outcome ( Oates, 2011 ; Pawson, 2006 ; Rousseau, Manning, & Denyer, 2008 ).

To circumvent these limitations, Pawson, Greenhalgh, Harvey, and Walshe (2005) have proposed a new approach for synthesizing knowledge that seeks to unpack the mechanism of how “complex interventions” work in particular contexts. The basic research question — what works? — which is usually associated with systematic reviews changes to: what is it about this intervention that works, for whom, in what circumstances, in what respects and why? Realist reviews have no particular preference for either quantitative or qualitative evidence. As a theory-building approach, a realist review usually starts by articulating likely underlying mechanisms and then scrutinizes available evidence to find out whether and where these mechanisms are applicable ( Shepperd et al., 2009 ). Primary studies found in the extant literature are viewed as case studies which can test and modify the initial theories ( Rousseau et al., 2008 ).

The main objective pursued in the realist review conducted by Otte-Trojel, de Bont, Rundall, and van de Klundert (2014) was to examine how patient portals contribute to health service delivery and patient outcomes. The specific goals were to investigate how outcomes are produced and, most importantly, how variations in outcomes can be explained. The research team started with an exploratory review of background documents and research studies to identify ways in which patient portals may contribute to health service delivery and patient outcomes. The authors identified six main ways which represent “educated guesses” to be tested against the data in the evaluation studies. These studies were identified through a formal and systematic search in four databases between 2003 and 2013. Two members of the research team selected the articles using a pre-established list of inclusion and exclusion criteria and following a two-step procedure. The authors then extracted data from the selected articles and created several tables, one for each outcome category. They organized information to bring forward those mechanisms where patient portals contribute to outcomes and the variation in outcomes across different contexts.

9.3.6. Critical Reviews

Lastly, critical reviews aim to provide a critical evaluation and interpretive analysis of existing literature on a particular topic of interest to reveal strengths, weaknesses, contradictions, controversies, inconsistencies, and/or other important issues with respect to theories, hypotheses, research methods or results ( Baumeister & Leary, 1997 ; Kirkevold, 1997 ). Unlike other review types, critical reviews attempt to take a reflective account of the research that has been done in a particular area of interest, and assess its credibility by using appraisal instruments or critical interpretive methods. In this way, critical reviews attempt to constructively inform other scholars about the weaknesses of prior research and strengthen knowledge development by giving focus and direction to studies for further improvement ( Kirkevold, 1997 ).

Kitsiou, Paré, and Jaana (2013) provide an example of a critical review that assessed the methodological quality of prior systematic reviews of home telemonitoring studies for chronic patients. The authors conducted a comprehensive search on multiple databases to identify eligible reviews and subsequently used a validated instrument to conduct an in-depth quality appraisal. Results indicate that the majority of systematic reviews in this particular area suffer from important methodological flaws and biases that impair their internal validity and limit their usefulness for clinical and decision-making purposes. To this end, they provide a number of recommendations to strengthen knowledge development towards improving the design and execution of future reviews on home telemonitoring.

9.4. Summary

Table 9.1 outlines the main types of literature reviews that were described in the previous sub-sections and summarizes the main characteristics that distinguish one review type from another. It also includes key references to methodological guidelines and useful sources that can be used by eHealth scholars and researchers for planning and developing reviews.

Typology of Literature Reviews (adapted from Paré et al., 2015).

As shown in Table 9.1 , each review type addresses different kinds of research questions or objectives, which subsequently define and dictate the methods and approaches that need to be used to achieve the overarching goal(s) of the review. For example, in the case of narrative reviews, there is greater flexibility in searching and synthesizing articles ( Green et al., 2006 ). Researchers are often relatively free to use a diversity of approaches to search, identify, and select relevant scientific articles, describe their operational characteristics, present how the individual studies fit together, and formulate conclusions. On the other hand, systematic reviews are characterized by their high level of systematicity, rigour, and use of explicit methods, based on an “a priori” review plan that aims to minimize bias in the analysis and synthesis process (Higgins & Green, 2008). Some reviews are exploratory in nature (e.g., scoping/mapping reviews), whereas others may be conducted to discover patterns (e.g., descriptive reviews) or involve a synthesis approach that may include the critical analysis of prior research ( Paré et al., 2015 ). Hence, in order to select the most appropriate type of review, it is critical to know before embarking on a review project, why the research synthesis is conducted and what type of methods are best aligned with the pursued goals.

9.5. Concluding Remarks

In light of the increased use of evidence-based practice and research generating stronger evidence ( Grady et al., 2011 ; Lyden et al., 2013 ), review articles have become essential tools for summarizing, synthesizing, integrating or critically appraising prior knowledge in the eHealth field. As mentioned earlier, when rigorously conducted review articles represent powerful information sources for eHealth scholars and practitioners looking for state-of-the-art evidence. The typology of literature reviews we used herein will allow eHealth researchers, graduate students and practitioners to gain a better understanding of the similarities and differences between review types.

We must stress that this classification scheme does not privilege any specific type of review as being of higher quality than another ( Paré et al., 2015 ). As explained above, each type of review has its own strengths and limitations. Having said that, we realize that the methodological rigour of any review — be it qualitative, quantitative or mixed — is a critical aspect that should be considered seriously by prospective authors. In the present context, the notion of rigour refers to the reliability and validity of the review process described in section 9.2. For one thing, reliability is related to the reproducibility of the review process and steps, which is facilitated by a comprehensive documentation of the literature search process, extraction, coding and analysis performed in the review. Whether the search is comprehensive or not, whether it involves a methodical approach for data extraction and synthesis or not, it is important that the review documents in an explicit and transparent manner the steps and approach that were used in the process of its development. Next, validity characterizes the degree to which the review process was conducted appropriately. It goes beyond documentation and reflects decisions related to the selection of the sources, the search terms used, the period of time covered, the articles selected in the search, and the application of backward and forward searches ( vom Brocke et al., 2009 ). In short, the rigour of any review article is reflected by the explicitness of its methods (i.e., transparency) and the soundness of the approach used. We refer those interested in the concepts of rigour and quality to the work of Templier and Paré (2015) which offers a detailed set of methodological guidelines for conducting and evaluating various types of review articles.

To conclude, our main objective in this chapter was to demystify the various types of literature reviews that are central to the continuous development of the eHealth field. It is our hope that our descriptive account will serve as a valuable source for those conducting, evaluating or using reviews in this important and growing domain.

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• Cite this Page Paré G, Kitsiou S. Chapter 9 Methods for Literature Reviews. In: Lau F, Kuziemsky C, editors. Handbook of eHealth Evaluation: An Evidence-based Approach [Internet]. Victoria (BC): University of Victoria; 2017 Feb 27.
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• Concluding Remarks

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A Maturity Level Framework for Practicing Machine Learning Operations in CI/CD For Software Deployment

• Muhammad Adeel Mannan Department of Computing, Faculty of Engineering Sciences and Technology (FEST), Hamdard University, Karachi, Pakistan
• Sumaira Mustafa Department of Computing, Faculty of Engineering Sciences and Technology (FEST), Hamdard University, Karachi, Pakistan
• Afzal Hussain Department of Computing, Faculty of Engineering Sciences and Technology (FEST), Hamdard University, Karachi, Pakistan.

Significantly shorter software development and deployment cycles have been made possible by the adoption of continuous software engineering techniques in business operations, such as DevOps (Development and Operations). Data scientists and operations teams have recently become more and more interested in a practice known as MLO (Machine Learning Operations). However, MLO adoption in practice is still in its early stages, and there aren't many established best practices for integrating it into current software development methods. In order to give a frame that outlines the way necessary in espousing MLO and the stages through which business capes process as they come riper and sophisticated, we achieve a methodical literature study as well as a slate review of literature in this composition. We test this approach in three example businesses and demonstrate how they were able to embrace and incorporate MLO into their massive software development businesses. This study offers three contributions. To give an overview of the state of the art in MLO, we first examine recent publications. Based on this analysis, we create an MLO framework that outlines the steps taken in the ongoing creation of machine learning models. Second, we define the several stages that businesses go through as they develop their MLO practices in a maturity model. Third, we map the firms to the maturity model phases and test our methodology using three embedded systems case companies. The main objective is to create an MLO framework.

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What is Software Development?

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Software development is the lifeblood of the digital age. It’s how we design, build, and maintain the software that powers everything from our smartphones to the complex systems running global businesses. The impact of software development is undeniable:

Explosive Growth: The global software market is poised to eclipse $600 billion by 2023 according to the Gartner report on the global software market. This highlights the vast reach and importance of software in our lives.

High Demand, High Reward: Software developers are in high demand, with the U.S. Bureau of Labor Statistics projecting a growth rate of 22% by 2030 – much faster than the average for all occupations.

In this guide, we’ll delve into the world of software development, exploring its significance, the essential skills involved, and how you can launch your career in this dynamic field.

Software development is the process of designing, writing (coding), testing, debugging, and maintaining the source code of computer programs. Picture it like this:

Software developers are the architects, builders, quality control, and renovation crew all in one! They turn ideas into the functional software that shapes our digital experiences.

This covers a lot of ground, from the websites and tools you use online, to the apps on your mobile devices, regular computer programs, big systems for running companies, and even the fun games you play.

Steps in the Software Development Process

Building software isn’t a haphazard process. It generally follows a structured lifecycle known as the Software Development Life Cycle (SDLC). Here’s an overview of its key phases:

1. Needs Identification

At this early stage, it’s all about figuring out the “why” of the software. What’s the issue you’re trying to solve for users? Will it simplify a business process? Will it create an exciting new entertainment experience? Or will it fill an existing market gap? For instance, an online retailer might recognize that their website’s recommendation engine needs to be improved in order to increase sales.

2. Requirement Analysis

Once the purpose is clear, the team delves into the detailed blueprint. They meticulously gather all the specific requirements the software must fulfill.  This includes defining features, how users will interact with the software, security considerations, and necessary performance levels. Continuing our example, the e-commerce company might determine requirements for personalized product suggestions, integration with their inventory system, and the ability to handle a high volume of users.

In this phase, software architects and designers create a structural plan.  They’ll choose the right technologies (programming languages, frameworks), decide how the software is broken into modules, and define how different components will interact.  For the recommendation engine, designers might opt for a cloud-based solution for scalability and use a machine learning library to power the suggestion algorithm.

4. Development and Implementation

This is where the building happens! Developers use their programming expertise to bring the design to life, writing the code that embodies the application’s logic and functionality.  Depending on the project’s complexity, multiple programming languages and tools might be involved. In our recommendation engine example, the team could utilize Python for the machine learning algorithm and a web framework like Flask to integrate it into their website.

A rigorous testing phase is crucial to ensure the software is bug-free and functions as intended.  Testers employ techniques like unit testing (checking individual code components), integration testing (how everything works together), and user acceptance testing (getting real-world feedback). In our scenario, testers will verify that the recommendation system suggests relevant products and gracefully handles different scenarios, such as when users have limited browsing history.

6. Deployment and Maintenance

It’s launch time! The software is deployed to its final environment, whether that’s release on an App Store, a live web application, or installation on company systems.  However, the journey doesn’t end here.  Continuous maintenance and updates are vital for security patches, addressing bugs, and adding new features down the line.

The SDLC can have different models (like Waterfall, and Agile). Real-world development often involves iterations and revisiting these stages.

Types of Software

The world of software is divided into broad categories, each serving a distinct purpose. Let’s explore these main types:

1. System Software

Think of system software as the foundation upon which your computer operates. It includes the operating system (like Windows, macOS, or Linux), which manages your computer’s hardware, provides a user interface, and enables you to run applications. Additionally, system software encompasses device drivers, the programs that allow your computer to communicate with devices like printers and webcams, and essential utilities like antivirus software and disk management tools.

2. Application Software

Application software is what you interact with directly to get things done, whether for work or play. This encompasses the programs you’re familiar with, such as web browsers (Chrome, Firefox), productivity suites (Microsoft Office, Google Workspace), video and photo editing software (Adobe Premiere Pro, Photoshop), games, and music streaming services like Spotify.

3. Programming Languages

Software coders use programming languages to create instructions. Programming languages also create application software and system software. Python, C++, Java, and C# are among the best known programming languages. Python is flexible and easy to learn for beginners, while Java is used in Android apps and enterprise programs. JavaScript makes websites interactive, while C++ is used for high-performance games and systems-level software development.

Important Note

While these categories are helpful, the lines between them can sometimes blur. For example, a web browser, though considered application software, heavily relies on components of your system software to function properly.

Why is Software Development Important?

Software development isn’t just about coding; it’s the engine driving progress in our modern world. Here’s why it matters:

The Fuel of Innovation: Breakthrough technologies like artificial intelligence, self-driving cars, and virtual reality would be impossible without sophisticated software. Software development pushes the boundaries of what’s possible, enabling entirely new industries and ways of interacting with the world.

Streamlining and Automating: From online banking to automated customer service chatbots, software makes processes faster, more convenient, and less prone to human error. This increased efficiency revolutionizes businesses and saves countless hours across various domains.

Adapting to Change: In our rapidly evolving world, software’s ability to be updated and modified is crucial. Whether it’s adapting to new regulations, customer needs, or technology trends, software empowers organizations to stay agile and remain competitive.

Global Reach: The internet and software transcend borders. Software-powered platforms connect people worldwide, facilitating remote work, global collaboration, and the rise of e-commerce, opening up markets once limited by geography.

Software Development’s Impact Across Industries

Let’s consider a few examples of how software changes the game in various sectors:

• Healthcare: Software powers medical imaging tools, analyzes vast datasets to discover new treatments and even assists with robot-guided surgery, ultimately improving patient care.
• Finance: Secure banking platforms, algorithmic trading, and fraud-detection software enable the flow of money while reducing risk.
• Education: Online learning platforms, interactive simulations, and adaptive learning tools make education more accessible and personalized for students of all ages.
• Transportation: Ride-hailing apps, traffic management systems, and developments in self-driving technology all rely on complex software systems.

Key Features of Software Development

Building high-quality software that meets user needs and endures over time requires a focus on these essential features:

Scalability: The ability of software to handle an increasing workload. Imagine a social media app: good software needs to work effortlessly whether it’s serving a few thousand users or millions. Scalability involves planning for growth and ensuring the system can expand gracefully.

Reliability: Users expect software to work consistently and as intended. Reliability encompasses thorough testing to minimize bugs and crashes, as well as implementing error-handling procedures to provide the best possible experience even when unexpected glitches occur.

Security: With cyberattacks on the rise, protecting user data and preventing unauthorized access is paramount. Secure software development includes careful encryption practices, safeguarding against common vulnerabilities, and constantly staying updated to address potential threats.

Flexibility: User needs change, technologies evolve, and new features are often desired.  Flexible software is designed to be adaptable and maintainable.  This makes it easier to introduce updates, integrate with other systems, and pivot in response to market changes.

Software Development Methodologies

Think of software development methodologies as different roadmaps to guide a software project from start to finish. Let’s explore some popular approaches:

Waterfall: The Traditional Approach

The Waterfall model is linear and sequential. It involves phases like requirements analysis, design, coding, testing, and then deployment. Each phase must be fully complete before moving on to the next. This approach is best suited for projects with very clear, unchanging requirements and a long development timeline.

Agile: Embracing Iteration

Agile methods like Scrum and Kanban focus on short development cycles (sprints), continuous feedback, and adaptability to change. They emphasize collaboration between developers, stakeholders, and end-users. Agile methodologies are well-suited for projects where requirements might shift or evolve, and where delivering working software quickly is a priority.

DevOps: Bridging Development and Operations

DevOps focuses on collaboration between development teams and IT operations.  It emphasizes automation, frequent updates, and monitoring to enable continuous delivery and rapid issue resolution.  The aim is to ensure faster releases with increased stability. This benefits businesses by allowing them to innovate quickly, delivering updates and features at a much faster pace while maintaining reliability.

Choosing the Right Methodology

The best methodology depends on factors like the project’s size and complexity, the clarity of requirements upfront, company culture, and the desired speed of delivery.

Modern Trends: Hybrid Approaches and Adaptability

Many organizations adopt variations or hybrid approaches, combining elements of different methodologies to suit their specific needs.  The ability to adapt the process itself is becoming a key hallmark of successful software development.

Software Development Tools and Solutions

Building software involves a whole toolkit beyond just coding skills. Let’s take a look at some commonly used categories of tools and technologies:

Integrated Development Environments (IDEs)

Think of IDEs as the developer’s powerhouse workspace. They combine a code editor, debugger, and compiler/interpreter, providing a streamlined experience. Popular IDEs include Visual Studio Code, IntelliJ IDEA, PyCharm, and Eclipse. IDEs boost productivity with features like code completion, syntax highlighting, and error checking, simplifying the overall development process.

Version Control Systems (e.g., Git)

Version control systems act like time travel for your code.  Git, the most widely used system, allows developers to track every change made, revert to older versions if needed, collaborate effectively, and maintain different branches of code for experimentation.  This provides a safety net, facilitates easy collaboration, and streamlines code management.

Project Management Tools (e.g., Jira, Trello)

These tools help organize tasks, set deadlines, and visualize the project’s progress. They often integrate with methodologies like Agile (Jira is particularly popular for this) and provide features like Kanban boards or Gantt charts to keep projects organized and efficient, especially within teams.

Collaboration Platforms (e.g., Slack, Microsoft Teams)

These platforms serve as a communication hub for development teams. They enable real-time messaging, file sharing, and video conferencing for seamless collaboration, reducing email overload and promoting quick problem-solving and knowledge sharing among team members.

Other Important Tools

• Cloud Computing Platforms (AWS, Azure, Google Cloud): Provide on-demand access to computing resources, databases, and a vast array of development tools.
• Testing Frameworks: Tools that help design and execute automated tests to ensure software quality.
• Web Frameworks (Django, Flask, Ruby on Rails): Offer structure and reusable components for building web applications.

Jobs That Use Software Development

• Quality Assurance (QA) Engineer: These professionals meticulously test software to identify bugs and ensure quality before release.  They employ both manual and automated testing methods, working closely with developers to enhance the final product.
• Computer Programmer: Computer Programmers focus on the core act of writing code. They use specific programming languages to translate software designs into functional programs.
• Database Administrator (DBA):   DBAs are responsible for the design, implementation, security, and performance optimization of database systems. They manage the storage, organization, and retrieval of an organization’s crucial data.
• Senior Systems Analyst: Systems Analysts act as a bridge between business needs and technical solutions.  They analyze an organization’s requirements, propose software solutions, and often oversee the development process to ensure the system meets its intended goals.
• Software Engineer: This is a broad term encompassing roles involved in designing, building, testing, and maintaining software applications. Software Engineers might specialize in areas like web development, mobile development, game development, or embedded systems.

Software Development Resources

Online courses and platforms.

• Beginner-friendly: Look for websites that have interactive lessons and guided projects to start with.
• Comprehensive Programs: Look for websites that cover a vast array of languages, frameworks, and specializations.
• Scaler’s Full-Stack Developer Course: A structured program with industry-relevant curriculum, experienced mentors, and strong community support.

Tutorials and Documentation

• Official Sources: Programming language websites (e.g., Python.org) and framework documentation provide the most reliable information.
• Community Hubs: Websites like Stack Overflow are phenomenal for troubleshooting and finding answers to common questions.

Coding Communities

• Online Forums: Engage with fellow learners, seek help, and discuss projects on platforms like Reddit (programming-related subreddits) or Discord servers dedicated to software development.
• Meetups: Network with developers in your area through local meetups and events.

How Scaler Can Help?

Scaler’s comprehensive Full-Stack Developer Course can be an accelerator on your software development journey. Consider the advantages:

• Structured Learning: A well-designed curriculum takes you systematically from core concepts to advanced applications, offering a clear path forward.
• Mentorship: Guidance from industry experts provides valuable insights and helps you overcome roadblocks.
• Projects and Practical Experience: Hands-on building solidifies learning and creates a portfolio to showcase your skills.
• Community and Career Support: Interaction with peers and access to career services can be beneficial as you navigate the journey into software development.

Learning software development is an ongoing process. Even experienced developers continue to explore new technologies and techniques.

• From ubiquitous applications to world-changing inventions that fuel global digitalization efforts in every sector, it is the software development that does all the creating.
• Designing, developing, testing and deploying are among the critical stages of the SDLC (Software Development Life Cycle).
• High-quality software should be scalable, safe and reliable. It must also perform well with good user experience while being easy to understand for other developers.
• With roles ranging from quality assurance engineers to software engineering engineers there are many opportunities available in different industries when it comes to software development.
• Continuous learning and community support are necessary for both beginners and experienced developers because of ever-evolving technologies which help them stay current within this domain of expertise or advance their careers further.

What is meant by a software developer?

A software developer is like an architect and construction crew combined. They design and build the software that powers everything from websites to complex enterprise systems.

What is the full form of SDLC?

SDLC stands for Software Development Life Cycle. It refers to the structured process of creating software, from defining requirements to deployment and maintenance.

Is software development the same as coding?

Coding (writing code) is a major part of software development, but it also involves problem-solving, design, testing, and collaboration.

What does a software developer do?

Software developers design, write code, test, debug, and maintain software applications. Their specific tasks depend on the project and their area of specialization.

What are some software development projects?

Software development projects can range from simple websites or mobile apps to complex enterprise systems, games, and even software for self-driving cars. The possibilities are endless!

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Methodological Approaches to Literature Review

• Living reference work entry
• First Online: 09 May 2023
• Cite this living reference work entry

• Dennis Thomas 2 ,
• Elida Zairina 3 &
• Johnson George 4  

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The literature review can serve various functions in the contexts of education and research. It aids in identifying knowledge gaps, informing research methodology, and developing a theoretical framework during the planning stages of a research study or project, as well as reporting of review findings in the context of the existing literature. This chapter discusses the methodological approaches to conducting a literature review and offers an overview of different types of reviews. There are various types of reviews, including narrative reviews, scoping reviews, and systematic reviews with reporting strategies such as meta-analysis and meta-synthesis. Review authors should consider the scope of the literature review when selecting a type and method. Being focused is essential for a successful review; however, this must be balanced against the relevance of the review to a broad audience.

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Centre of Excellence in Treatable Traits, College of Health, Medicine and Wellbeing, University of Newcastle, Hunter Medical Research Institute Asthma and Breathing Programme, Newcastle, NSW, Australia

Dennis Thomas

Department of Pharmacy Practice, Faculty of Pharmacy, Universitas Airlangga, Surabaya, Indonesia

Elida Zairina

Centre for Medicine Use and Safety, Monash Institute of Pharmaceutical Sciences, Faculty of Pharmacy and Pharmaceutical Sciences, Monash University, Parkville, VIC, Australia

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Thomas, D., Zairina, E., George, J. (2023). Methodological Approaches to Literature Review. In: Encyclopedia of Evidence in Pharmaceutical Public Health and Health Services Research in Pharmacy. Springer, Cham. https://doi.org/10.1007/978-3-030-50247-8_57-1

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Data visualisation in scoping reviews and evidence maps on health topics: a cross-sectional analysis

• Emily South   ORCID: orcid.org/0000-0003-2187-4762 1 &
• Mark Rodgers 1  

Systematic Reviews volume  12 , Article number:  142 ( 2023 ) Cite this article

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Scoping reviews and evidence maps are forms of evidence synthesis that aim to map the available literature on a topic and are well-suited to visual presentation of results. A range of data visualisation methods and interactive data visualisation tools exist that may make scoping reviews more useful to knowledge users. The aim of this study was to explore the use of data visualisation in a sample of recent scoping reviews and evidence maps on health topics, with a particular focus on interactive data visualisation.

Ovid MEDLINE ALL was searched for recent scoping reviews and evidence maps (June 2020-May 2021), and a sample of 300 papers that met basic selection criteria was taken. Data were extracted on the aim of each review and the use of data visualisation, including types of data visualisation used, variables presented and the use of interactivity. Descriptive data analysis was undertaken of the 238 reviews that aimed to map evidence.

Of the 238 scoping reviews or evidence maps in our analysis, around one-third (37.8%) included some form of data visualisation. Thirty-five different types of data visualisation were used across this sample, although most data visualisations identified were simple bar charts (standard, stacked or multi-set), pie charts or cross-tabulations (60.8%). Most data visualisations presented a single variable (64.4%) or two variables (26.1%). Almost a third of the reviews that used data visualisation did not use any colour (28.9%). Only two reviews presented interactive data visualisation, and few reported the software used to create visualisations.

Conclusions

Data visualisation is currently underused by scoping review authors. In particular, there is potential for much greater use of more innovative forms of data visualisation and interactive data visualisation. Where more innovative data visualisation is used, scoping reviews have made use of a wide range of different methods. Increased use of these more engaging visualisations may make scoping reviews more useful for a range of stakeholders.

Peer Review reports

Scoping reviews are “a type of evidence synthesis that aims to systematically identify and map the breadth of evidence available on a particular topic, field, concept, or issue” ([ 1 ], p. 950). While they include some of the same steps as a systematic review, such as systematic searches and the use of predetermined eligibility criteria, scoping reviews often address broader research questions and do not typically involve the quality appraisal of studies or synthesis of data [ 2 ]. Reasons for conducting a scoping review include the following: to map types of evidence available, to explore research design and conduct, to clarify concepts or definitions and to map characteristics or factors related to a concept [ 3 ]. Scoping reviews can also be undertaken to inform a future systematic review (e.g. to assure authors there will be adequate studies) or to identify knowledge gaps [ 3 ]. Other evidence synthesis approaches with similar aims have been described as evidence maps, mapping reviews or systematic maps [ 4 ]. While this terminology is used inconsistently, evidence maps can be used to identify evidence gaps and present them in a user-friendly (and often visual) way [ 5 ].

Scoping reviews are often targeted to an audience of healthcare professionals or policy-makers [ 6 ], suggesting that it is important to present results in a user-friendly and informative way. Until recently, there was little guidance on how to present the findings of scoping reviews. In recent literature, there has been some discussion of the importance of clearly presenting data for the intended audience of a scoping review, with creative and innovative use of visual methods if appropriate [ 7 , 8 , 9 ]. Lockwood et al. suggest that innovative visual presentation should be considered over dense sections of text or long tables in many cases [ 8 ]. Khalil et al. suggest that inspiration could be drawn from the field of data visualisation [ 7 ]. JBI guidance on scoping reviews recommends that reviewers carefully consider the best format for presenting data at the protocol development stage and provides a number of examples of possible methods [ 10 ].

Interactive resources are another option for presentation in scoping reviews [ 9 ]. Researchers without the relevant programming skills can now use several online platforms (such as Tableau [ 11 ] and Flourish [ 12 ]) to create interactive data visualisations. The benefits of using interactive visualisation in research include the ability to easily present more than two variables [ 13 ] and increased engagement of users [ 14 ]. Unlike static graphs, interactive visualisations can allow users to view hierarchical data at different levels, exploring both the “big picture” and looking in more detail ([ 15 ], p. 291). Interactive visualizations are often targeted at practitioners and decision-makers [ 13 ], and there is some evidence from qualitative research that they are valued by policy-makers [ 16 , 17 , 18 ].

Given their focus on mapping evidence, we believe that scoping reviews are particularly well-suited to visually presenting data and the use of interactive data visualisation tools. However, it is unknown how many recent scoping reviews visually map data or which types of data visualisation are used. The aim of this study was to explore the use of data visualisation methods in a large sample of recent scoping reviews and evidence maps on health topics. In particular, we were interested in the extent to which these forms of synthesis use any form of interactive data visualisation.

This study was a cross-sectional analysis of studies labelled as scoping reviews or evidence maps (or synonyms of these terms) in the title or abstract.

The search strategy was developed with help from an information specialist. Ovid MEDLINE® ALL was searched in June 2021 for studies added to the database in the previous 12 months. The search was limited to English language studies only.

The search strategy was as follows:

Ovid MEDLINE(R) ALL

(scoping review or evidence map or systematic map or mapping review or scoping study or scoping project or scoping exercise or literature mapping or evidence mapping or systematic mapping or literature scoping or evidence gap map).ab,ti.

limit 1 to english language

(202006* or 202007* or 202008* or 202009* or 202010* or 202011* or 202012* or 202101* or 202102* or 202103* or 202104* or 202105*).dt.

The search returned 3686 records. Records were de-duplicated in EndNote 20 software, leaving 3627 unique records.

A sample of these reviews was taken by screening the search results against basic selection criteria (Table 1 ). These criteria were piloted and refined after discussion between the two researchers. A single researcher (E.S.) screened the records in EPPI-Reviewer Web software using the machine-learning priority screening function. Where a second opinion was needed, decisions were checked by a second researcher (M.R.).

Our initial plan for sampling, informed by pilot searching, was to screen and data extract records in batches of 50 included reviews at a time. We planned to stop screening when a batch of 50 reviews had been extracted that included no new types of data visualisation or after screening time had reached 2 days. However, once data extraction was underway, we found the sample to be richer in terms of data visualisation than anticipated. After the inclusion of 300 reviews, we took the decision to end screening in order to ensure the study was manageable.

Data extraction

A data extraction form was developed in EPPI-Reviewer Web, piloted on 50 reviews and refined. Data were extracted by one researcher (E. S. or M. R.), with a second researcher (M. R. or E. S.) providing a second opinion when needed. The data items extracted were as follows: type of review (term used by authors), aim of review (mapping evidence vs. answering specific question vs. borderline), number of visualisations (if any), types of data visualisation used, variables/domains presented by each visualisation type, interactivity, use of colour and any software requirements.

When categorising review aims, we considered “mapping evidence” to incorporate all of the six purposes for conducting a scoping review proposed by Munn et al. [ 3 ]. Reviews were categorised as “answering a specific question” if they aimed to synthesise study findings to answer a particular question, for example on effectiveness of an intervention. We were inclusive with our definition of “mapping evidence” and included reviews with mixed aims in this category. However, some reviews were difficult to categorise (for example where aims were unclear or the stated aims did not match the actual focus of the paper) and were considered to be “borderline”. It became clear that a proportion of identified records that described themselves as “scoping” or “mapping” reviews were in fact pseudo-systematic reviews that failed to undertake key systematic review processes. Such reviews attempted to integrate the findings of included studies rather than map the evidence, and so reviews categorised as “answering a specific question” were excluded from the main analysis. Data visualisation methods for meta-analyses have been explored previously [ 19 ]. Figure  1 shows the flow of records from search results to final analysis sample.

Flow diagram of the sampling process

Data visualisation was defined as any graph or diagram that presented results data, including tables with a visual mapping element, such as cross-tabulations and heat maps. However, tables which displayed data at a study level (e.g. tables summarising key characteristics of each included study) were not included, even if they used symbols, shading or colour. Flow diagrams showing the study selection process were also excluded. Data visualisations in appendices or supplementary information were included, as well as any in publicly available dissemination products (e.g. visualisations hosted online) if mentioned in papers.

The typology used to categorise data visualisation methods was based on an existing online catalogue [ 20 ]. Specific types of data visualisation were categorised in five broad categories: graphs, diagrams, tables, maps/geographical and other. If a data visualisation appeared in our sample that did not feature in the original catalogue, we checked a second online catalogue [ 21 ] for an appropriate term, followed by wider Internet searches. These additional visualisation methods were added to the appropriate section of the typology. The final typology can be found in Additional file 1 .

We conducted descriptive data analysis in Microsoft Excel 2019 and present frequencies and percentages. Where appropriate, data are presented using graphs or other data visualisations created using Flourish. We also link to interactive versions of some of these visualisations.

Almost all of the 300 reviews in the total sample were labelled by review authors as “scoping reviews” ( n  = 293, 97.7%). There were also four “mapping reviews”, one “scoping study”, one “evidence mapping” and one that was described as a “scoping review and evidence map”. Included reviews were all published in 2020 or 2021, with the exception of one review published in 2018. Just over one-third of these reviews ( n  = 105, 35.0%) included some form of data visualisation. However, we excluded 62 reviews that did not focus on mapping evidence from the following analysis (see “ Methods ” section). Of the 238 remaining reviews (that either clearly aimed to map evidence or were judged to be “borderline”), 90 reviews (37.8%) included at least one data visualisation. The references for these reviews can be found in Additional file 2 .

Number of visualisations

Thirty-six (40.0%) of these 90 reviews included just one example of data visualisation (Fig.  2 ). Less than a third ( n  = 28, 31.1%) included three or more visualisations. The greatest number of data visualisations in one review was 17 (all bar or pie charts). In total, 222 individual data visualisations were identified across the sample of 238 reviews.

Number of data visualisations per review

Categories of data visualisation

Graphs were the most frequently used category of data visualisation in the sample. Over half of the reviews with data visualisation included at least one graph ( n  = 59, 65.6%). The least frequently used category was maps, with 15.6% ( n  = 14) of these reviews including a map.

Of the total number of 222 individual data visualisations, 102 were graphs (45.9%), 34 were tables (15.3%), 23 were diagrams (10.4%), 15 were maps (6.8%) and 48 were classified as “other” in the typology (21.6%).

Types of data visualisation

All of the types of data visualisation identified in our sample are reported in Table 2 . In total, 35 different types were used across the sample of reviews.

The most frequently used data visualisation type was a bar chart. Of 222 total data visualisations, 78 (35.1%) were a variation on a bar chart (either standard bar chart, stacked bar chart or multi-set bar chart). There were also 33 pie charts (14.9% of data visualisations) and 24 cross-tabulations (10.8% of data visualisations). In total, these five types of data visualisation accounted for 60.8% ( n  = 135) of all data visualisations. Figure  3 shows the frequency of each data visualisation category and type; an interactive online version of this treemap is also available ( https://public.flourish.studio/visualisation/9396133/ ). Figure  4 shows how users can further explore the data using the interactive treemap.

Data visualisation categories and types. An interactive version of this treemap is available online: https://public.flourish.studio/visualisation/9396133/ . Through the interactive version, users can further explore the data (see Fig.  4 ). The unit of this treemap is the individual data visualisation, so multiple data visualisations within the same scoping review are represented in this map. Created with flourish.studio ( https://flourish.studio )

Screenshots showing how users of the interactive treemap can explore the data further. Users can explore each level of the hierarchical treemap ( A Visualisation category >  B Visualisation subcategory >  C Variables presented in visualisation >  D Individual references reporting this category/subcategory/variable permutation). Created with flourish.studio ( https://flourish.studio )

Data presented

Around two-thirds of data visualisations in the sample presented a single variable ( n  = 143, 64.4%). The most frequently presented single variables were themes ( n  = 22, 9.9% of data visualisations), population ( n  = 21, 9.5%), country or region ( n  = 21, 9.5%) and year ( n  = 20, 9.0%). There were 58 visualisations (26.1%) that presented two different variables. The remaining 21 data visualisations (9.5%) presented three or more variables. Figure  5 shows the variables presented by each different type of data visualisation (an interactive version of this figure is available online).

Variables presented by each data visualisation type. Darker cells indicate a larger number of reviews. An interactive version of this heat map is available online: https://public.flourish.studio/visualisation/10632665/ . Users can hover over each cell to see the number of data visualisations for that combination of data visualisation type and variable. The unit of this heat map is the individual data visualisation, so multiple data visualisations within a single scoping review are represented in this map. Created with flourish.studio ( https://flourish.studio )

Most reviews presented at least one data visualisation in colour ( n  = 64, 71.1%). However, almost a third ( n  = 26, 28.9%) used only black and white or greyscale.

Interactivity

Only two of the reviews included data visualisations with any level of interactivity. One scoping review on music and serious mental illness [ 22 ] linked to an interactive bubble chart hosted online on Tableau. Functionality included the ability to filter the studies displayed by various attributes.

The other review was an example of evidence mapping from the environmental health field [ 23 ]. All four of the data visualisations included in the paper were available in an interactive format hosted either by the review management software or on Tableau. The interactive versions linked to the relevant references so users could directly explore the evidence base. This was the only review that provided this feature.

Software requirements

Nine reviews clearly reported the software used to create data visualisations. Three reviews used Tableau (one of them also used review management software as discussed above) [ 22 , 23 , 24 ]. Two reviews generated maps using ArcGIS [ 25 ] or ArcMap [ 26 ]. One review used Leximancer for a lexical analysis [ 27 ]. One review undertook a bibliometric analysis using VOSviewer [ 28 ], and another explored citation patterns using CitNetExplorer [ 29 ]. Other reviews used Excel [ 30 ] or R [ 26 ].

To our knowledge, this is the first systematic and in-depth exploration of the use of data visualisation techniques in scoping reviews. Our findings suggest that the majority of scoping reviews do not use any data visualisation at all, and, in particular, more innovative examples of data visualisation are rare. Around 60% of data visualisations in our sample were simple bar charts, pie charts or cross-tabulations. There appears to be very limited use of interactive online visualisation, despite the potential this has for communicating results to a range of stakeholders. While it is not always appropriate to use data visualisation (or a simple bar chart may be the most user-friendly way of presenting the data), these findings suggest that data visualisation is being underused in scoping reviews. In a large minority of reviews, visualisations were not published in colour, potentially limiting how user-friendly and attractive papers are to decision-makers and other stakeholders. Also, very few reviews clearly reported the software used to create data visualisations. However, 35 different types of data visualisation were used across the sample, highlighting the wide range of methods that are potentially available to scoping review authors.

Our results build on the limited research that has previously been undertaken in this area. Two previous publications also found limited use of graphs in scoping reviews. Results were “mapped graphically” in 29% of scoping reviews in any field in one 2014 publication [ 31 ] and 17% of healthcare scoping reviews in a 2016 article [ 6 ]. Our results suggest that the use of data visualisation has increased somewhat since these reviews were conducted. Scoping review methods have also evolved in the last 10 years; formal guidance on scoping review conduct was published in 2014 [ 32 ], and an extension of the PRISMA checklist for scoping reviews was published in 2018 [ 33 ]. It is possible that an overall increase in use of data visualisation reflects increased quality of published scoping reviews. There is also some literature supporting our findings on the wide range of data visualisation methods that are used in evidence synthesis. An investigation of methods to identify, prioritise or display health research gaps (25/139 included studies were scoping reviews; 6/139 were evidence maps) identified 14 different methods used to display gaps or priorities, with half being “more advanced” (e.g. treemaps, radial bar plots) ([ 34 ], p. 107). A review of data visualisation methods used in papers reporting meta-analyses found over 200 different ways of displaying data [ 19 ].

Only two reviews in our sample used interactive data visualisation, and one of these was an example of systematic evidence mapping from the environmental health field rather than a scoping review (in environmental health, systematic evidence mapping explicitly involves producing a searchable database [ 35 ]). A scoping review of papers on the use of interactive data visualisation in population health or health services research found a range of examples but still limited use overall [ 13 ]. For example, the authors noted the currently underdeveloped potential for using interactive visualisation in research on health inequalities. It is possible that the use of interactive data visualisation in academic papers is restricted by academic publishing requirements; for example, it is currently difficult to incorporate an interactive figure into a journal article without linking to an external host or platform. However, we believe that there is a lot of potential to add value to future scoping reviews by using interactive data visualisation software. Few reviews in our sample presented three or more variables in a single visualisation, something which can easily be achieved using interactive data visualisation tools. We have previously used EPPI-Mapper [ 36 ] to present results of a scoping review of systematic reviews on behaviour change in disadvantaged groups, with links to the maps provided in the paper [ 37 ]. These interactive maps allowed policy-makers to explore the evidence on different behaviours and disadvantaged groups and access full publications of the included studies directly from the map.

We acknowledge there are barriers to use for some of the data visualisation software available. EPPI-Mapper and some of the software used by reviews in our sample incur a cost. Some software requires a certain level of knowledge and skill in its use. However numerous online free data visualisation tools and resources exist. We have used Flourish to present data for this review, a basic version of which is currently freely available and easy to use. Previous health research has been found to have used a range of different interactive data visualisation software, much of which does not required advanced knowledge or skills to use [ 13 ].

There are likely to be other barriers to the use of data visualisation in scoping reviews. Journal guidelines and policies may present barriers for using innovative data visualisation. For example, some journals charge a fee for publication of figures in colour. As previously mentioned, there are limited options for incorporating interactive data visualisation into journal articles. Authors may also be unaware of the data visualisation methods and tools that are available. Producing data visualisations can be time-consuming, particularly if authors lack experience and skills in this. It is possible that many authors prioritise speed of publication over spending time producing innovative data visualisations, particularly in a context where there is pressure to achieve publications.

Limitations

A limitation of this study was that we did not assess how appropriate the use of data visualisation was in our sample as this would have been highly subjective. Simple descriptive or tabular presentation of results may be the most appropriate approach for some scoping review objectives [ 7 , 8 , 10 ], and the scoping review literature cautions against “over-using” different visual presentation methods [ 7 , 8 ]. It cannot be assumed that all of the reviews that did not include data visualisation should have done so. Likewise, we do not know how many reviews used methods of data visualisation that were not well suited to their data.

We initially relied on authors’ own use of the term “scoping review” (or equivalent) to sample reviews but identified a relatively large number of papers labelled as scoping reviews that did not meet the basic definition, despite the availability of guidance and reporting guidelines [ 10 , 33 ]. It has previously been noted that scoping reviews may be undertaken inappropriately because they are seen as “easier” to conduct than a systematic review ([ 3 ], p.6), and that reviews are often labelled as “scoping reviews” while not appearing to follow any established framework or guidance [ 2 ]. We therefore took the decision to remove these reviews from our main analysis. However, decisions on how to classify review aims were subjective, and we did include some reviews that were of borderline relevance.

A further limitation is that this was a sample of published reviews, rather than a comprehensive systematic scoping review as have previously been undertaken [ 6 , 31 ]. The number of scoping reviews that are published has increased rapidly, and this would now be difficult to undertake. As this was a sample, not all relevant scoping reviews or evidence maps that would have met our criteria were included. We used machine learning to screen our search results for pragmatic reasons (to reduce screening time), but we do not see any reason that our sample would not be broadly reflective of the wider literature.

Data visualisation, and in particular more innovative examples of it, is currently underused in published scoping reviews on health topics. The examples that we have found highlight the wide range of methods that scoping review authors could draw upon to present their data in an engaging way. In particular, we believe that interactive data visualisation has significant potential for mapping the available literature on a topic. Appropriate use of data visualisation may increase the usefulness, and thus uptake, of scoping reviews as a way of identifying existing evidence or research gaps by decision-makers, researchers and commissioners of research. We recommend that scoping review authors explore the extensive free resources and online tools available for data visualisation. However, we also think that it would be useful for publishers to explore allowing easier integration of interactive tools into academic publishing, given the fact that papers are now predominantly accessed online. Future research may be helpful to explore which methods are particularly useful to scoping review users.

Availability of data and materials

The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

Abbreviations

Organisation formerly known as Joanna Briggs Institute

Preferred Reporting Items for Systematic Reviews and Meta-Analyses

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Acknowledgements

We would like to thank Melissa Harden, Senior Information Specialist, Centre for Reviews and Dissemination, for advice on developing the search strategy.

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Both authors conceptualised and designed the study and contributed to screening, data extraction and the interpretation of results. ES undertook the literature searches, analysed data, produced the data visualisations and drafted the manuscript. MR contributed to revising the manuscript, and both authors read and approved the final version.

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Additional file 1..

Typology of data visualisation methods.

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References of scoping reviews included in main dataset.

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Machine learning models for abstract screening task - A systematic literature review application for health economics and outcome research

• Jingcheng Du 1 ,
• Ekin Soysal 1 , 3 ,
• Dong Wang 2 ,
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• Jingqi Wang 1 ,
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Systematic literature reviews (SLRs) are critical for life-science research. However, the manual selection and retrieval of relevant publications can be a time-consuming process. This study aims to (1) develop two disease-specific annotated corpora, one for human papillomavirus (HPV) associated diseases and the other for pneumococcal-associated pediatric diseases (PAPD), and (2) optimize machine- and deep-learning models to facilitate automation of the SLR abstract screening.

This study constructed two disease-specific SLR screening corpora for HPV and PAPD, which contained citation metadata and corresponding abstracts. Performance was evaluated using precision, recall, accuracy, and F1-score of multiple combinations of machine- and deep-learning algorithms and features such as keywords and MeSH terms.

Results and conclusions

The HPV corpus contained 1697 entries, with 538 relevant and 1159 irrelevant articles. The PAPD corpus included 2865 entries, with 711 relevant and 2154 irrelevant articles. Adding additional features beyond title and abstract improved the performance (measured in Accuracy) of machine learning models by 3% for HPV corpus and 2% for PAPD corpus. Transformer-based deep learning models that consistently outperformed conventional machine learning algorithms, highlighting the strength of domain-specific pre-trained language models for SLR abstract screening. This study provides a foundation for the development of more intelligent SLR systems.

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Introduction

Systematic literature reviews (SLRs) are an essential tool in many areas of health sciences, enabling researchers to understand the current knowledge around a topic and identify future research and development directions. In the field of health economics and outcomes research (HEOR), SLRs play a crucial role in synthesizing evidence around unmet medical needs, comparing treatment options, and preparing the design and execution of future real-world evidence studies. SLRs provide a comprehensive and transparent analysis of available evidence, allowing researchers to make informed decisions and improve patient outcomes.

Conducting a SLR involves synthesizing high-quality evidence from biomedical literature in a transparent and reproducible manner, and seeks to include all available evidence on a given research question, and provides some assessment regarding quality of the evidence [ 1 , 2 ]. To conduct an SLR one or more bibliographic databases are queried based on a given research question and a corresponding set of inclusion and exclusion criteria, resulting in the selection of a relevant set of abstracts. The abstracts are reviewed, further refining the set of articles that are used to address the research question. Finally, appropriate data is systematically extracted from the articles and summarized [ 1 , 3 ].

The current approach to conducting a SLR is through manual review, with data collection, and summary done by domain experts against pre-specified eligibility criteria. This is time-consuming, labor-intensive, expensive, and non-scalable given the current more-than linear growth of the biomedical literature [ 4 ]. Michelson and Reuter estimate that each SLR costs approximately $141,194.80 and that on average major pharmaceutical companies conduct 23.36 SLRs, and major academic centers 177.32 SLRs per year, though the cost may vary based on the scope of different reviews [ 4 ]. Clearly automated methods are needed, both from a cost/time savings perspective, and for the ability to effectively scan and identify increasing amounts of literature, thereby allowing the domain experts to spend more time analyzing the data and gleaning the insights.

One major task of SLR project that involves large amounts of manual effort, is the abstract screening task. For this task, selection criteria are developed and the citation metadata and abstract for articles tentatively meeting these criteria are retrieved from one or more bibliographic databases (e.g., PubMed). The abstracts are then examined in more detail to determine if they are relevant to the research question(s) and should be included or excluded from further consideration. Consequently, the task of determining whether articles are relevant or not based on their titles, abstracts and metadata can be treated as a binary classification task, which can be addressed by natural language processing (NLP). NLP involves recognizing entities and relationships expressed in text and leverages machine-learning (ML) and deep-learning (DL) algorithms together with computational semantics to extract information. The past decade has witnessed significant advances in these areas for biomedical literature mining. A comprehensive review on how NLP techniques in particular are being applied for automatic mining and knowledge extraction from biomedical literature can be found in Zhao et al. [ 5 ].

Materials and methods

The aims of this study were to: (1) identify and develop two disease-specific corpora, one for human papillomavirus (HPV) associated diseases and the other for pneumococcal-associated pediatric diseases suitable for training the ML and DL models underlying the necessary NLP functions; (2) investigate and optimize the performance of the ML and DL models using different sets of features (e.g., keywords, Medical Subject Heading (MeSH) terms [ 6 ]) to facilitate automation of the abstract screening tasks necessary to construct a SLR. Note that these screening corpora can be used as training data to build different NLP models. We intend to freely share these two corpora with the entire scientific community so they can serve as benchmark corpora for future NLP model development in this area.

SLR corpora preparation

Two completed disease-specific SLR studies by Merck & Co., Inc., Rahway, NJ, USA were used as the basis to construct corpora for abstract-level screening. The two SLR studies were both relevant to health economics and outcome research, including one for human papillomavirus (HPV) associated diseases (referred to as the HPV corpus), and one for pneumococcal-associated pediatric diseases (which we refer to as the PAPD corpus). Both of the original SLR studies contained literature from PubMed/MEDLINE and EMBASE. Since we intended for the screening corpora to be released to the community, we only kept citations found from PubMed/MEDLINE in the finalized corpora. Because the original SLR studies did not contain the PubMed ID (PMID) for each article, we matched each article’s citation information (if available) against PubMed and then collected meta-data such as authors, journals, keywords, MeSH terms, publication types, etc., using PubMed Entrez Programming Utilities (E-utilities) Application Programming Interface (API). The detailed description of the two corpora can be seen in Table  1 . Both of the resulting corpora are publicly available at [ https://github.com/Merck/NLP-SLR-corpora ].

Machine learning algorithms

Although deep learning algorithms have demonstrated superior performance on many NLP tasks, conventional machine learning algorithms have certain advantages, such as low computation costs and faster training and prediction speed.

We evaluated four traditional ML-based document classification algorithms, XGBoost [ 7 ], Support Vector Machines (SVM) [ 8 ], Logistic regression (LR) [ 9 ], and Random Forest [ 10 ] on the binary inclusion/exclusion classification task for abstract screening. Salient characteristics of these models are as follows:

XGBoost: Short for “eXtreme Gradient Boosting”, XGBoost is a boosting-based ensemble of algorithms that turn weak learners into strong learners by focusing on where the individual models went wrong. In Gradient Boosting, individual weak models train upon the difference between the prediction and the actual results [ 7 ]. We set max_depth at 3, n_estimators at 150 and learning rate at 0.7.

Support vector machine (SVM): SVM is one of the most robust prediction methods based on statistical learning frameworks. It aims to find a hyperplane in an N-dimensional space (where N = the number of features) that distinctly classifies the data points [ 8 ]. We set C at 100, gamma at 0.005 and kernel as radial basis function.

Logistic regression (LR): LR is a classic statistical model that in its basic form uses a logistic function to model a binary dependent variable [ 9 ]. We set C at 5 and penalty as l2.

Random forest (RF): RF is a machine learning technique that utilizes ensemble learning to combine many decision trees classifiers through bagging or bootstrap aggregating [ 10 ]. We set n_estimators at 100 and max_depth at 14.

These four algorithms were trained for both the HPV screening task and the PAPD screening task using the corresponding training corpus.

For each of the four algorithms, we examined performance using (1) only the baseline feature criteria (title and abstract of each article), and (2) with five additional meta-data features (MeSH, Authors, Keywords, Journal, Publication types.) retrieved from each article using the PubMed E-utilities API. Conventionally, title and abstract are the first information a human reviewer would depend on when making a judgment for inclusion or exclusion of an article. Consequently, we used title and abstract as the baseline features to classify whether an abstract should be included at the abstract screening stage. We further evaluated the performance with additional features that can be retrieved by PubMed E-utilities API, including MeSH terms, authors, journal, keywords and publication type. For baseline evaluation, we concatenated the titles and abstracts and extracted the TF-IDF (term frequency-inverse document frequency) vector for the corpus. TF-IDF evaluates how relevant a word is to a document in a collection of documents. For additional features, we extracted TF-IDF vector using each feature respectively and then concatenated the extracted vectors with title and abstract vector. XGBoost was selected for the feature evaluation process, due to its relatively quick computational running time and robust performance.

Deep learning algorithms

Conventional ML methods rely heavily on manually designed features and suffer from the challenges of data sparsity and poor transportability when applied to new use cases. Deep learning (DL) is a set of machine learning algorithms based on deep neural networks that has advanced performance of text classification along with many other NLP tasks. Transformer-based deep learning models, such as BERT (Bidirectional encoder representations from transformers), have achieved state-of-the-art performance in many NLP tasks [ 11 ]. A Transformer is an emerging architecture of deep learning models designed to handle sequential input data such as natural language by adopting the mechanisms of attention to differentially weigh the significance of each part of the input data [ 12 ]. The BERT model and its variants (which use Transformer as a basic unit) leverage the power of transfer learning by first pre-training the models over 100’s of millions of parameters using large volumes of unlabeled textual data. The resulting model is then fine-tuned for a particular downstream NLP application, such as text classification, named entity recognition, relation extraction, etc. The following three BERT models were evaluated against both the HPV and Pediatric pneumococcal corpus using two sets of features (title and abstract versus adding all additional features into the text). For all BERT models, we used Adam optimizer with weight decay. We set learning rate at 1e-5, batch size at 8 and number of epochs at 20.

BERT base: this is the original BERT model released by Google. The BERT base model was pre-trained on textual data in the general domain, i.e., BooksCorpus (800 M words) and English Wikipedia (2500 M words) [ 11 ].

BioBERT base: as the biomedical language is different from general language, the BERT models trained on general textual data may not work well on biomedical NLP tasks. BioBERT was further pre-trained (based on original BERT models) in the large-scale biomedical corpora, including PubMed abstracts (4.5B words) and PubMed Central Full-text articles (13.5B words) [ 13 ].

PubMedBERT: PubMedBERT was pre-trained from scratch using abstracts from PubMed. This model has achieved state-of-the-art performance on several biomedical NLP tasks on Biomedical Language Understanding and Reasoning Benchmark [ 14 ].

Text pre-processing and libraries that were used

We have removed special characters and common English words as a part of text pre-processing. Default tokenizer from scikit-learn was adopted for tokenization. Scikit-learn was also used for TF-IDF feature extraction and machine learning algorithms implementation. Transformers libraries from Hugging Face were used for deep learning algorithms implementation.

Evaluation datasets were constructed from the HPV and Pediatric pneumococcal corpora and were split into training, validation and testing sets with a ratio of 8:1:1 for the two evaluation tasks: (1) ML algorithms performance assessment; and (2) DL algorithms performance assessment. Models were fitted on the training sets, and model hyperparameters were optimized on the validation sets and the performance were evaluated on the testing sets. The following major metrics are expressed by the noted calculations:

Where True positive is an outcome where the model correctly predicts the positive (e.g., “included” in our tasks) class. Similarly, a True negative is an outcome where the model correctly predicts the negative class (e.g., “excluded” in our tasks). False positive is an outcome where the model incorrectly predicts the positive class, and a False negative is an outcome where the model incorrectly predicts the negative class. We have repeated all experiments five times and reported the mean scores with standard deviation.

Table  2 shows the baseline comparison using different feature combinations for the SLR text classification tasks using XGBoost. As noted, adding additional features in addition to title and abstract was effective in further improving the classification accuracy. Specifically, using all available features for the HPV classification increased accuracy by ? ∼  3% and F1 score by ? ∼  3%; using all available features for Pediatric pneumococcal classification increased accuracy by ? ∼  2% and F1 score by ? ∼  4%. As observed, adding additional features provided a stronger boost in precision, which contributed to the overall performance improvement.

The comparison of the article inclusion/exclusion classification task for four machine learning algorithms with all features is shown in Table  3 . XGBoost achieved the highest accuracy and F-1 scores in both tasks. Table  4 shows the comparison between XGBoost and deep learning algorithms on the classification tasks for each disease. Both XGBoost and deep learning models consistently have achieved higher accuracy scores when using all features as input. Among all models, BioBERT has achieved the highest accuracy at 0.88, compared with XGBoost at 0.86. XGBoost has the highest F1 score at 0.8 and the highest recall score at 0.9 for inclusion prediction.

Discussions and conclusions

Abstract screening is a crucial step in conducting a systematic literature review (SLR), as it helps to identify relevant citations and reduces the effort required for full-text screening and data element extraction. However, screening thousands of abstracts can be a time-consuming and burdensome task for scientific reviewers. In this study, we systematically investigated the use of various machine learning and deep learning algorithms, using different sets of features, to automate abstract screening tasks. We evaluated these algorithms using disease-focused SLR corpora, including one for human papillomavirus (HPV) associated diseases and another for pneumococcal-associated pediatric diseases (PADA). The publicly available corpora used in this study can be used by the scientific community for advanced algorithm development and evaluation. Our findings suggest that machine learning and deep learning algorithms can effectively automate abstract screening tasks, saving valuable time and effort in the SLR process.

Although machine learning and deep learning algorithms trained on the two SLR corpora showed some variations in performance, there were also some consistencies. Firstly, adding additional citation features significantly improved the performance of conventional machine learning algorithms, although the improvement was not as strong in transformer-based deep learning models. This may be because transformer models were mostly pre-trained on abstracts, which do not include additional citation information like MeSH terms, keywords, and journal names. Secondly, when using only title and abstract as input, transformer models consistently outperformed conventional machine learning algorithms, highlighting the strength of subject domain-specific pre-trained language models. When all citation features were combined as input, conventional machine learning algorithms showed comparable performance to deep learning models. Given the much lower computation costs and faster training and prediction time, XGBoost or support vector machines with all citation features could be an excellent choice for developing an abstract screening system.

Some limitations remain for this study. Although we’ve evaluated cutting-edge machine learning and deep learning algorithms on two SLR corpora, we did not conduct much task-specific customization to the learning algorithms, including task-specific feature engineering and rule-based post-processing, which could offer additional benefits to the performance. As the focus of this study is to provide generalizable strategies for employing machine learning to abstract screening tasks, we leave the task-specific customization to future improvement. The corpora we evaluated in this study mainly focus on health economics and outcome research, the generalizability of learning algorithms to another domain will benefit from formal examination.

Extensive studies have shown the superiority of transformer-based deep learning models for many NLP tasks [ 11 , 13 , 14 , 15 , 16 ]. Based on our experiments, however, adding features to the pre-trained language models that have not seen these features before may not significantly boost their performance. It would be interesting to find a better way of encoding additional features to these pre-trained language models to maximize their performance. In addition, transfer learning has proven to be an effective technique to improve the performance on a target task by leveraging annotation data from a source task [ 17 , 18 , 19 ]. Thus, for a new SLR abstract screening task, it would be worthwhile to investigate the use of transfer learning by adapting our (publicly available) corpora to the new target task.

When labeled data is available, supervised machine learning algorithms can be very effective and efficient for article screening. However, as there is increasing need for explainability and transparency in NLP-assisted SLR workflow, supervised machine learning algorithms are facing challenges in explaining why certain papers fail to fulfill the criteria. The recent advances in large language models (LLMs), such as ChatGPT [ 20 ] and Gemini [ 21 ], show remarkable performance on NLP tasks and good potentials in explainablity. Although there are some concerns on the bias and hallucinations that LLMs could bring, it would be worthwhile to evaluate further how LLMs could be applied to SLR tasks and understand the performance of using LLMs to take free-text article screening criteria as the input and provide explainanation for article screening decisions.

Data availability

The annotated corpora underlying this article are available at https://github.com/Merck/NLP-SLR-corpora .

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Acknowledgements

We thank Dr. Majid Rastegar-Mojarad for conducting some additional experiments during revision.

This research was supported by Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA.

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Dong Wang, Yeran Li, Elise Wu & Lixia Yao

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Study concept and design: JD and LY Corpus preparation: DW, YL and LY Experiments: JD and ES Draft of the manuscript: JD, DW, FJM and LY Acquisition, analysis, or interpretation of data: JD, ES, DW and LY Critical revision of the manuscript for important intellectual content: JD, ES, DW, LH, BL, JW, FJM, YL, EW, LY Study supervision: LY.

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DW is an employee of Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA. EW, YL, and LY were employees of Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA for this work. JD, LH, JW, and FJM are employees of Intelligent Medical Objects. ES was an employee of Intelligent Medical Objects during his contributions, and is currently an employee of EBSCO Information Services. All the other authors declare no competing interest.

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Du, J., Soysal, E., Wang, D. et al. Machine learning models for abstract screening task - A systematic literature review application for health economics and outcome research. BMC Med Res Methodol 24 , 108 (2024). https://doi.org/10.1186/s12874-024-02224-3

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Efficacy and safety of mirror therapy for post-stroke aphasia: A systematic review and meta-analysis protocol

Roles Writing – original draft

Affiliation School of Medical Technology and Information Engineering, Zhejiang Chinese Medical University, Hangzhou, China

Roles Software

Affiliation Department of Emergency Medicine, Taihe Hospital, Hubei, China

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* E-mail: [email protected]

• Yufeng Peng, 
• Shouqiang Huang, 
• Xiaotong Yang, 

• Published: May 8, 2024
• https://doi.org/10.1371/journal.pone.0301468
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• Reader Comments

Aphasia is one of the most common complications of stroke. Mirror therapy (MT) is promising rehabilitation measure for the treatment of post-stroke aphasia. Although some studies suggested that MT is effective and safe for aphasia, the effects and safety remain uncertain due to lacking strong evidence, such as the relevant systematic review and meta- analysis.

This study will search PubMed, Web of Science, Cochrane Library, EMBASE, Medline, China Knowledge Network (CNKI), WANFANG, China Biomedical Literature Database (CBM), from inception to 1 th May 2023 to identify any eligible study. No language or date of publication shall be limited. We will only include randomised controlled trials of MT in the Treatment of poststroke aphasia. Two investigators will work separately on the study selection, data extraction, and study quality assessment. The western aphasia battery (WAB) and aphasia quotient (AQ) will be included as the main outcomes. Boston diagnostic aphasia examination method (BDAE), Chinese standard aphasia examination (CRRCAE) will be included as the secondary outcomes. The statistical analysis will be conducted by RevMan V.5.4 software. The risk of bias of included studies will be assessed by the Cochrane ‘Risk of bias’ tool. The quality of proof of the results will be evaluated by using the Grading of Recommendations Assessment, Development and Evaluation guidelines.

The finding will be presented in a journal or related conferences.

This study will provide a basis for whether mirror therapy (MT) is effective and safe in the treatment of post-stroke aphasia.

Trial registration

Systematic review registration

INPLASY registration number: INPLASY 202340054 .

Citation: Peng Y, Huang S, Yang X, Ma J (2024) Efficacy and safety of mirror therapy for post-stroke aphasia: A systematic review and meta-analysis protocol. PLoS ONE 19(5): e0301468. https://doi.org/10.1371/journal.pone.0301468

Editor: Nadinne Alexandra Roman, Transilvania University of Brasov: Universitatea Transilvania din Brasov, ROMANIA

Received: August 2, 2023; Accepted: March 13, 2024; Published: May 8, 2024

Copyright: © 2024 Peng et al. This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Data Availability: All relevant data are within the paper and its Supporting information files.

Funding: The authors received no specific funding for this work.

Competing interests: The authors have declared that no competing interests exist.

Introduction

There are more than 10 million new cases of stroke worldwide each year, and at least one third of these patients present with aphasia [ 1 , 2 ]. Post-stroke aphasia is an acquired language disorder in which patients have impairments in all aspects of the language system [ 3 ], mainly including difficulties in auditory comprehension, spontaneous speech, repetition and naming [ 4 ]. Different patients have different manifestations of aphasia. Even within the same patient, symptoms related to aphasia can vary considerably, especially in the first weeks and months after stroke. The different types and severity of aphasia depend on many factors, including the size and location of the stroke, health status, time to recovery from stroke, and time since stroke [ 5 ]. Although many stroke survivors show spontaneous partial speech recovery, between one-third and one-half of these patients continue to suffer from speech dysfunction 6 months after the stroke [ 6 ]. Post-stroke aphasia can adversely affect daily life and work as well as communication skills and lead to a higher incidence of depression in patients [ 7 ]. However, treatment options for patients with this disorder remain relatively limited, such as speech therapy and pharmacological interventions. Therefore, it is crucial to develop new and effective approaches to treat this language disorder.

Mirror therapy is a kind of motor representation training based on action observation, visual imagery and imitation learning [ 8 ]. During the training process, a mirror device is used to copy the image of the activity of the healthy side of the limb to the affected side, and the patient stimulates the main motor cortex of the human brain through such visual feedback, which affects the electrical activity and excitability of the cortex and promotes brain function remodeling and induces motor function recovery [ 9 ]. Mirror neurons are specialized neurons with mapping functions, visual connectivity, and motor feedback; mirror neurons are activated both when performing motor tasks and when observing the same movements; therefore, mirror neurons are considered to be an important neural basis for understanding movements, imitating behaviors, language learning, and attention shifting [ 10 , 11 ]. In mirror training, by activating relevant mirror neurons, especially in the inferior frontal gyrus and pre motor cortex and inferior parietal lobule [ 12 ], thereby improving aphasia and spatial attentional function in stroke patients [ 13 ]. Many recent studies have attempted to use the mirror neuron theory to treat different forms of aphasia [ 13 , 14 ]. In one study, real MT was found to significantly improve language function in stroke patients compared to sham MT [ 15 ].

Mirror therapy has the advantages of safety, effectiveness, convenience and non-invasive, which can intervene in the early stage of stroke Aphasia and promote the recovery of speech function. Although numerous clinical studies have reported positive effects of mirror therapy on aphasia after stroke, there is no meta-analysis available. Therefore, this review conducts a meta-analysis to assess the efficacy and safety of mirror therapy for poststroke aphasia and provides a stronger basis for clinical treatment.

This study will complete in accordance with the Preferred Reporting Initiative for Systematic Reviews and Meta-Analysis Project (PRISMA-P) guidelines [ 16 ]. This systematic review program was registered on the INPLASY website. Registration number: INPLASY202340054。As this study will be based on published studies, ethical approval is not required. The PRISMA-P checklist is attached as S1 File .

Selection criteria

Types of participants..

Patients with aphasia after stroke and older than 18 years old. All patients should be diagnosed with stroke by CT or MRI and confirmed by the clinician of aphasia presentation. However, gender, race and educational status are not restricted, to the exclusion of participants who are unable to cooperate with rehabilitation, such as hearing, visual and cognitive impairments or severe infections, organ malfunctions, etc.

Types of interventions.

The interventions considered in the experimental group consist of mirror therapy. The control group will receive conventional speech rehabilitation therapy

Types of outcomes

(1) The primary outcomes

The western aphasia battery (WAB) and aphasia quotient (AQ) will be included as the main outcomes. The WAB is an internationally standardized test of aphasia, and consists of four subtests: spontaneous speech, auditory comprehension, repetition, and naming. AQ will be calculated based on the aphasia quotient = (spontaneous speech + listening comprehension/20 + repetition/10 + naming/10) × 2.

(2) The secondary outcomes

Additional outcomes will be assessed using the Boston Diagnostic Aphasia Examination (BDAE), Chinese Standardized Review of Aphasia (CRRCAE), Communication Activities of Daily Living (CADL), Functional Assessment of Communication Skills (FACS) and Hamilton Depression Scale (HAM-D).

Types of study.

This study will only include randomised controlled clinical trials (RCTs) of MT for poststroke aphasia. Studies will be excluded if they are conference papers, editorials, abstract opinions, case reports, and crossover studies.

Search strategy

Electronic searches..

We will search the following electronic databases from creation to 1 May 2023: Cochrane Library, EMBASE, Medline, Web of Science, Pubmed, the Chinese Biomedical Literature Database, the electronic databases of the WanFang Data and China National Knowledge Infrastructure. The following medical keywords: "mirror therapy", "aphasia", and " stroke" will be used in this search. No language or date of publication shall be limited. Details of the research strategy in the Pubmed database are presented in S1 Table .

Searching other resources.

Other ongoing and unpublished clinical trial registry studies will be reviewed to find additional eligible studies.

Data extraction and export

We will confirm the standard data extraction form prior to data extraction. Based on the requirements, the two researchers will independently review the literature. By reviewing the titles and abstracts, they will first use EndNote X 9.0 to weed out duplicate articles and remove those that don’t meet the inclusion requirements. Secondly, they will read the full text based on the inclusion and exclusion criteria and screen the remaining articles again. Finally, they will register the excluded articles and explain the reasons and decide whether they are ready for a systematic analysis. In the event of a dispute, a third researcher will be asked for guidance and to mediate a resolution. Fig 1 depicts the exact screening procedure.

• PPT PowerPoint slide
• PNG larger image
• TIFF original image

https://doi.org/10.1371/journal.pone.0301468.g001

Data extraction and analysis

The data will be extracted independently by two researchers using a predetermined standard Excel spreadsheet. This includes general information (authors, age, sex, country, race, year of publication, diagnostic criteria); study design (sample size, randomization and blinding details); details of interventions (treatment method, frequency, treatment time); and outcome indicators (primary and secondary outcomes, adverse events and others). Any disagreements between two investigators will be resolved by negotiation with a third investigator.

Assessment of risk of bias in included studies

The quality of the included trials will be assessed using the Cochrane Collaboration’s tool by two reviewers (PYF and HSQ). We will assess the risk of bias from the following seven domains: 1. random sequence generation; 2. allocation sequence concealment; 3. blinding of participants and staff; 4. blinding of outcome assessment; 5. incomplete outcome data; 6. selective reporting; 7. other biases. Assessments will be categorized as low risk, high risk, and uncertain risk, and any disagreements between two investigators will be resolved by negotiation between a third investigator.

Measures of treatment effect

If continuous data are included, mean difference (MD) or standard MD (SMD) will be used to calculate the treatment effect with a 95% confidence interval. If dichotomous data are present, the risk ratio (RR) and 95% confidence interval (CI) will be produced.

Dealing with missing data

In order to obtain the missing data, we will make an effort to contact with the authors by phone or email. If still not available, we will perform an intention-to-treat analysis for missing participant data. At the same times, we will evaluate the potential impact for the missing data by performing sensitivity analysis.

Assessment of heterogeneity

We will test heterogeneity by I 2 test. If I 2 is less than 50%, it means that there is no significant heterogeneity; if I 2 is greater than 50%, there is substantial heterogeneity. To investigate the causes of the heterogeneity in the study results, subgroup analysis and sensitivity analysis will be used.

Data synthesis

The software Review Manager V.5.4 will be used to carry out the meta-analysis. Continuous data will be presented as the standardized mean difference (SMD) with a 95% confidence interval, whereas dichotomous data will be reported as the risk ratio (RR) with a 95% confidence interval (CI). The significance level will be set at 50% for the Higgins I 2 test, which will be used to examine heterogeneity. For the goal of meta-analysis, a model with fixed effects will be employed if heterogeneity is not considerable (I 2 ≤ 50%). If heterogeneity is significant (I 2 ≥50%), a random effects model will be used. We will perform sensitivity analysis and subgroup analysis to find their potential explanations.

Assessment of publication biases

When more than ten studies are included, funnel plots will be generated to analyzed the potential reporting biases. If the distribution of funnel plot data is relatively symmetrical, that means no publication bias.

Subgroup analysis

If possible, a subgroup analysis will be performed by the characteristics of the studies. Variations in the factors including intervention type, treatment duration, age, sample size and quality of studies, will be considered.

Sensitivity analysis

To check the stability and dependability of the study’s findings, the researchers will repeat the sensitivity analysis. One study at a time will be removed to confirm that the results are not influenced by any one study. The outcomes of the data analysis will then be compared once more; if there is no change, the results are steady and trustworthy.

Evidence quality evaluation

The quality of evidence for each outcome will be assessed using the Grading of Recommendations Assessment, Development and Evaluation guidelines [ 17 ]. The evaluation items mainly stem from following factors: the risk of bias, imprecision, inconsistency, indirectness, publication bias [ 17 , 18 ]. According to above factors, the assessments will be graded into very low, low, moderate or high level.

Ethics and communication

Ethical approval is not required as individual patient data is not required in this study. The findings of this review will be presented at conferences or in peer-reviewed journal articles.

Aphasia is common following stroke, with frequencies ranging from 15 to 42 percent in acute settings and from 25 to 50 percent in chronic settings [ 19 ], and 32%-50% of patients with aphasia still have language impairment 6 months after stroke or even for the rest of their lives [ 20 ], which affects patients’ communication, daily life, work and recreation to varying degrees. The efficacy of current medication or speech rehabilitation is limited, so it is important to explore effective treatment methods for post-stroke aphasia.

In recent years, the field of brain and cognitive science has developed rapidly, and mirror neurons are one of the most significant discoveries in this field [ 21 ]. Many new rehabilitation therapies based on mirror neuron theory, such as motor observation therapy, motor imagery therapy, mirror therapy, virtual reality therapy, and brain-computer interface technology, have been translated into stroke rehabilitation [ 22 ].

MT is based on the mirror neuron system, which uses the planar mirror imaging principle of contralateral active image projection onto the affected side. It also combines visual illusion, visual feedback and virtual reality, and also has the advantages of simplicity, convenience, effectiveness and no pharmacological side effects [ 23 ].

It has been shown to be effective in improving upper limb motor function in stroke patients with hemiplegia and reducing pain in patients with regional pain syndrome [ 23 ]. Furthermore, it has been shown that supplementing conventional speech rehabilitation with mirror therapy can improve the aphasia quotient of the Western Aphasia Battery in patients with aphasia [ 24 ]. In addition, MT training in the acute post-stroke period can facilitate the recovery of language function in patients with motor aphasia. This intervention significantly strengthened the functional connectivity between the frontal, temporal, and parietal lobes of the left hemisphere brain and reinforced the connection with the hippocampus, suggesting that MT training can promote language recovery and reveal the underlying neuroplasticity mechanism of language recovery after stroke [ 15 ].

However, there is no systematic review and meta-analysis on this issue, The effectiveness and safety of MT in adult patients with post-stroke aphasia will thus be the focus of the first systematic review and meta-analysis in this field. This study offers scientifically sound medical support for this disease’s treatment. The study has a number of restrictions. First, heterogeneity may exist because most of the included studies differed in method selection, site selection, treatment frequency, and treatment duration. Second, most of the literature included in this study was in Chinese, which may have led to language selection bias.

Supporting information

S1 table. search strategy..

https://doi.org/10.1371/journal.pone.0301468.s001

S1 File. PRISMA-P-checklist.

https://doi.org/10.1371/journal.pone.0301468.s002

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