developmental psychology hypothesis

Developmental Psychology 101: Theories, Stages, & Research

You can imagine how vast this field of psychology is if it has to cover the whole of life, from birth through death.

Just like any other area of psychology, it has created exciting debates and given rise to fascinating case studies.

In recent years, developmental psychology has shifted to incorporate positive psychology paradigms to create a holistic lifespan approach. As an example, the knowledge gained from positive psychology can enhance the development of children in education.

In this article, you will learn a lot about different aspects of developmental psychology, including how it first emerged in history and famous theories and models.

Before you continue, we thought you might like to download our three Positive Psychology Exercises for free . These science-based exercises explore fundamental aspects of positive psychology, including strengths, values, and self-compassion, and will give you the tools to enhance the wellbeing of your clients, students, or employees.

This Article Contains:

What is developmental psychology, 4 popular theories, stages, & models, 2 questions and research topics, fascinating case studies & research findings, a look at positive developmental psychology, applying developmental psychology in education, resources from positivepsychology.com, a take-home message.

Human beings change drastically over our lifetime.

The American Psychological Association (2020) defines developmental psychology as the study of physical, mental, and behavioral changes, from conception through old age.

Developmental psychology investigates biological, genetic, neurological, psychosocial, cultural, and environmental factors of human growth (Burman, 2017).

Over the years, developmental psychology has been influenced by numerous theories and models in varied branches of psychology (Burman, 2017).

History of developmental psychology

Developmental psychology first appeared as an area of study in the late 19th century (Baltes, Lindenberger, & Staudinger, 2007). Developmental psychology focused initially on child and adolescent development, and was concerned about children’s minds and learning (Hall, 1883).

There are several key figures in developmental psychology. In 1877, the famous evolutionary biologist Charles Darwin undertook the first study of developmental psychology on innate communication forms. Not long after, physiologist William Preyer (1888) published a book on the abilities of an infant.

The 1900s saw many significant people dominating the developmental psychology field with their detailed theories of development: Sigmund Freud (1923, 1961), Jean Piaget (1928), Erik Erikson (1959), Lev Vygotsky (1978), John Bowlby (1958), and Albert Bandura (1977).

By the 1920s, the scope of developmental psychology had begun to include adult development and the aging process (Thompson, 2016).

In more recent years, it has broadened further to include prenatal development (Brandon et al., 2009). Developmental psychology is now understood to encompass the complete lifespan (Baltes et al., 2007).

Each of these models has contributed to the understanding of the process of human development and growth.

Furthermore, each theory and model focuses on different aspects of development: social, emotional, psychosexual, behavioral, attachment, social learning, and many more.

Here are some of the most popular models of development that have heavily contributed to the field of developmental psychology.

1. Bowlby’s attachment styles

The seminal work of psychologist John Bowlby (1958) showcased his interest in children’s social development. Bowlby (1969, 1973, 1980) developed the most famous theory of social development, known as attachment theory .

Bowlby (1969) hypothesized that the need to form attachments is innate, embedded in all humans for survival and essential for children’s development. This instinctive bond helps ensure that children are cared for by their parent or caregiver (Bowlby, 1969, 1973, 1980).

Bowlby’s original attachment work was developed further by one of his students, Mary Ainsworth. She proposed several attachment styles between the child and the caregiver (Ainsworth & Bell, 1970).

This theory clearly illustrates the importance of attachment styles to a child’s future development. Consistent and stable caregiving results in a secure attachment style (Ainsworth, Blehar, Waters, & Wall, 1978). In contrast, unstable and insecure caregiving results in several negative attachment styles: ambivalent, avoidant, or disorganized (Ainsworth & Bell, 1970; Main & Solomon, 1986).

Bowlby’s theory does not consider peer group influence or how it can shape children’s personality and development (Harris, 1998).

2. Piaget’s stage theory

Jean Piaget was a French psychologist highly interested in child development. He was interested in children’s thinking and how they acquire, construct, and use their knowledge (Piaget, 1951).

Piaget’s (1951) four-stage theory of cognitive development sequences a child’s intellectual development. According to this theory, all children move through these four stages of development in the same order (Simatwa, 2010).

The sensorimotor stage is from birth to two years old. Behaviors are triggered by sensory stimuli and limited to simple motor responses. If an object is removed from the child’s vision, they think it no longer exists (Piaget, 1936).

The pre-operational stage occurs between two and six years old. The child learns language but cannot mentally manipulate information or understand concrete logic (Wadsworth, 1971).

The concrete operational stage takes place from 7 to 11 years old. Children begin to think more logically about factual events. Abstract or hypothetical concepts are still difficult to understand in this stage (Wadsworth, 1971).

In the formal operational stage from 12 years to adulthood, abstract thought and skills arise (Piaget, 1936).

Piaget did not consider other factors that might affect these stages or a child’s progress through them. Biological maturation and interaction with the environment can determine the rate of cognitive development in children (Papalia & Feldman, 2011). Individual differences can also dictate a child’s progress (Berger, 2014).

3. Freud’s psychosexual development theory

One of the most influential developmental theories, which encompassed psychosexual stages of development, was developed by Austrian psychiatrist Sigmund Freud (Fisher & Greenberg, 1996).

Freud concluded that childhood experiences and unconscious desires influence behavior after witnessing his female patients experiencing physical symptoms and distress with no physical cause (Breuer & Freud, 1957).

According to Freud’s psychosexual theory, child development occurs in a series of stages, each focused on different pleasure areas of the body. During each stage, the child encounters conflicts, which play a significant role in development (Silverman, 2017).

Freud’s theory of psychosexual development includes the oral, anal, phallic, latent, and genital stages. His theory suggests that the energy of the libido is focused on these different erogenous zones at each specific stage (Silverman, 2017).

Freud concluded that the successful completion of each stage leads to healthy adult development. He also suggested that a failure to progress through a stage causes fixation and developmental difficulties, such as nail biting (oral fixation) or obsessive tidiness (anal fixation; Silverman, 2017).

Freud considered personality to be formed in childhood as a child passes through these stages. Criticisms of Freud’s theory of psychosexual development include its failure to consider that personality can change and grow over an entire lifetime. Freud believed that early experiences played the most significant role in shaping development (Silverman, 2017).

4. Bandura’s social learning theory

American psychologist Albert Bandura proposed the social learning theory (Bandura, Ross, & Ross, 1961). Bandura did not believe that classical or operant conditioning was enough to explain learned behavior because some behaviors of children are never reinforced (Bandura, 1986). He believed that children observe, imitate, and model the behaviors and reactions of others (Bandura, 1977).

Bandura suggested that observation is critical in learning. Further, the observation does not have to be of a live actor, such as in the Bobo doll experiment (Bandura, 1986). Bandura et al. (1961) considered that learning and modeling can also occur from listening to verbal instructions on behavior performance.

Bandura’s (1977) social theory posits that both environmental and cognitive factors interact to influence development.

Bandura’s developmental theory has been criticized for not considering biological factors or children’s autonomic nervous system responses (Kevin, 1995).

Overview of theories of development – Khan Academy

Developmental psychology has given rise to many debatable questions and research topics. Here are two of the most commonly discussed.

1. Nature vs nurture debate

One of the oldest debates in the field of developmental psychology has been between nature and nurture (Levitt, 2013).

Is human development a result of hereditary factors (genes), or is it influenced by the environment (school, family, relationships, peers, community, culture)?

The polarized position of developmental psychologists of the past has now changed. The nature/nurture question now concerns the relationship between the innateness of an attribute and the environmental effects on that attribute (Nesterak, 2015).

The field of epigenetics  describes how behavioral and environmental influences affect the expression of genes (Kubota, Miyake, & Hirasawa, 2012).

Many severe mental health disorders have a hereditary component. Yet, the environment and behavior, such as improved diet, reduced stress, physical activity, and a positive mindset, can determine whether this health condition is ever expressed (Śmigielski, Jagannath, Rössler, Walitza, & Grünblatt, 2020).

When considering classic models of developmental psychology, such as Piaget’s schema theory and Freud’s psychosexual theory, you’ll see that they both perceive development to be set in stone and unchangeable by the environment.

Contemporary developmental psychology theories take a different approach. They stress the importance of multiple levels of organization over the course of human development (Lomas, Hefferon, & Ivtzan, 2016).

2. Theory of mind

Theory of mind allows us to understand that others have different intentions, beliefs, desires, perceptions, behaviors, and emotions (American Psychological Association, 2020).

It was first identified by research by Premack and Woodruff (1978) and considered to be a natural developmental stage of progression for all children. Starting around the ages of four or five, children begin to think about the thoughts and feelings of others. This shows an emergence of the theory of mind (Wellman & Liu, 2004).

However, the ability of all individuals to achieve and maintain this critical skill at the same level is debatable.

Children diagnosed with autism exhibit a deficit in the theory of mind (Baron-Cohen, Leslie, & Frith, 1985).

Individuals with depression (psychotic and non-psychotic) are significantly impaired in theory of mind tasks (Wang, Wang, Chen, Zhu, & Wang, 2008).

People with social anxiety disorder have also been found to show less accuracy in decoding the mental states of others (Washburn, Wilson, Roes, Rnic, & Harkness, 2016).

Further research has shown that the theory of mind changes with aging. This suggests a developmental lifespan process for this concept (Meinhardt-Injac, Daum, & Meinhardt, 2020).

1. Little Albert

The small child who was the focus of the experiments of behavioral psychologists Watson and Rayner (1920) was referred to as ‘Little Albert.’ These experiments were essential landmarks in developmental psychology and showed how an emotionally stable child can be conditioned to develop a phobia.

Albert was exposed to several neutral stimuli including cotton wool, masks, a white rat, rabbit, monkey, and dog. Albert showed no initial fear to these stimuli.

When a loud noise was coupled with the initially neutral stimulus, Albert became very distressed and developed a phobia of the object, which extended to any similar object as well.

This experiment highlights the importance of environmental factors in the development of behaviors in children.

2. David Reimer

At the age of eight months, David Reimer lost his penis in a circumcision operation that went wrong. His worried parents consulted a psychologist, who advised them to raise David as a girl.

David’s young age meant he knew nothing about this. He went through the process of hormonal treatment and gender reassignment. At the age of 14, David found out the truth and wanted to reverse the gender reassignment process to become a boy again. He had always felt like a boy until this time, even though he was socialized and brought up as a girl (Colapinto, 2006).

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Contemporary theories of developmental psychology often encompass a holistic approach and a more positive approach to development.

Positive psychology has intersected with developmental disciplines in areas such as parenting, education, youth, and aging (Lomas et al., 2016).

These paradigms can all be grouped together under the umbrella of positive developmental psychology. This fresh approach to development focuses on the wellbeing aspects of development, while systematically bringing them together (Lomas, et al., 2016).

• Positive parenting is the approach to children’s wellbeing by focusing on the role of parents and caregivers (Latham, 1994).
• Positive education looks at flourishing in the context of school (Seligman, Ernst, Gillham, Reivich, & Linkins, 2009).
• Positive youth development is the productive and constructive focus on adolescence and early adulthood to enhance young people’s strengths and promote positive outcomes (Larson, 2000).
• Positive aging , also known as healthy aging, focuses on the positivity of aging as a healthy, normal stage of life (Vaillant, 2004).

Much of the empirical and theoretical work connected to positive developmental psychology has been going on for years, even before the emergence of positive psychology itself (Lomas et al., 2016).

We recommend this related article Applying Positive Psychology in Schools & Education: Your Ultimate Guide for further reading.

In the classroom, developmental psychology considers children’s psychological, emotional, and intellectual characteristics according to their developmental stage.

A report on the top 20 principles of psychology in the classroom, from pre-kindergarten to high school, was published by the American Psychological Association in 2015. The report also advised how teachers can respond to these principles in the classroom setting.

The top 5 principles and teacher responses are outlined in the table below.

There are many valuable resources to help you foster positive development no matter whether you’re working with young children, teenagers, or adults.

To help get you started, check out the following free resources from around our blog.

• Adopt A Growth Mindset This exercise helps clients recognize instances of fixed mindset in their thinking and actions and replace them with thoughts and behaviors more supportive of a growth mindset.
• Childhood Frustrations This worksheet provides a space for clients to document key challenges experienced during childhood, together with their emotional and behavioral responses.
• What I Want to Be This worksheet helps children identify behaviors and emotions they would like to display and select an opportunity in the future to behave in this ideal way.
• 17 Positive Psychology Exercises If you’re looking for more science-based ways to help others enhance their wellbeing, this signature collection contains 17 validated positive psychology tools for practitioners. Use them to help others flourish and thrive.
• Developmental Psychology Courses If you are interested in a career in Developmental Psychology , we suggest 15 of the best courses in this article.

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Expand your arsenal and impact with these 17 Positive Psychology Exercises [PDF] , scientifically designed to promote human flourishing, meaning, and wellbeing.

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Earlier developmental psychology models and theories were focused on specific areas, such as attachment, psychosexual, cognitive, and social learning. Although informative, they did not take in differing perspectives and were fixed paradigms.

We’ve now come to understand that development is not fixed. Individual differences take place in development, and the factors that can affect development are many. It is ever changing throughout life.

The modern-day approach to developmental psychology includes sub-fields of positive psychology. It brings these differing disciplines together to form an overarching positive developmental psychology paradigm.

Developmental psychology has helped us gain a considerable understanding of children’s motivations, social and emotional contexts, and their strengths and weaknesses.

This knowledge is essential for educators to create rich learning environments for students to help them develop positively and ultimately flourish to their full potential.

We hope you enjoyed reading this article. Don’t forget to download our three Positive Psychology Exercises for free .

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The Oxford Handbook of Developmental Psychology, Vol. 1: Body and Mind

Philip David Zelazo, Ph.D., is the Nancy M. and John E. Lindahl Professor at the Institute of Child Development, University of Minnesota. His research has been recognized by numerous awards and honors, he serves on several editorial boards (e.g., Child Development; Emotion; Development and Psychopathology), and he is currently the President of the Jean Piaget Society. In 2007, he was the lead Editor of The Cambridge Handbook of Consciousness.

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This volume synthesizes and integrates the broad literature in the subdisciplines of developmental psychology. The volume features an opening chapter by the volume editor outlining the organization of the field, as well as a concluding chapter in which the volume editor outlines future directions for developmental psychology. This volume synthesizes the developmental psychological literatures in such areas as biological development, behavioral genetics, visual development, auditory and musical development, object perception, cognitive development, memory, spatial development, categorization, imitation, development of attention, reasoning, imagination, moral development, speech perception, syntax acquisition, and gesture.

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Developmental Psychology

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• First Online: 17 December 2022
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• Moritz M. Daum 5 , 6 &
• Mirella Manfredi 5  

Part of the book series: Springer International Handbooks of Education ((SIHE))

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Developmental Psychology is the scientific study of mind and behavior from the perspective of change across the entire lifespan. In the present chapter, we provide a comprehensive and modern view on current topics particularly relevant when teaching Developmental Psychology. We start with the attempt to derive a contemporary definition of development and Developmental Psychology. Over historical time, perspectives on development changed. These different perspectives were regularly challenged, and we discuss some of the questions of scientific dispute such as the influence of nature and nurture on the development of an individual from a contemporary perspective. The perspectives often resulted in larger theoretical constructs. We will not describe individual theories comprehensively but rather focus on general issues of theoretical approaches and highlight one recent approach, the dynamic systems theories. Theories need to be supported by empirical evidence. Accordingly, we will briefly describe the major research designs used to measure developmental change. We will conclude the chapter with a focus on one topic particularly relevant when teaching Developmental Psychology, the development of communication, and discuss further topics that can potentially be included in a Developmental Psychology curriculum and describe some ideas on how to teach them. In all, we intend to provide a contemporary overview of the scientific study of developmental change.

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Daum, M.M., Manfredi, M. (2023). Developmental Psychology. In: Zumbach, J., Bernstein, D.A., Narciss, S., Marsico, G. (eds) International Handbook of Psychology Learning and Teaching. Springer International Handbooks of Education. Springer, Cham. https://doi.org/10.1007/978-3-030-28745-0_13

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Developmental Psychology: Definition and Uses

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Developmental psychology is a field that studies how people grow and change throughout the course of their lifespans. Development is about much more than the physical changes that occur over a lifetime. It also involves cognitive, social, and emotional changes at different ages.

This article discusses some of the major issues in developmental psychology and the historical origins of some of the best-known development theories. It also covers the goals and impact of developmental psychology.

Table of Contents

What Is Developmental Psychology?

Developmental psychology focuses on studying how individuals change and develop throughout their lifespan. It examines the physical, cognitive, emotional, and social changes from infancy to age. Developmental psychologists seek to understand the processes and factors influencing human development, such as genetics, environment, culture, and individual experiences.

Key areas of interest within developmental psychology include:

Child Development

This area focuses on children’s physical, cognitive, and emotional development from infancy through adolescence. Researchers study topics like language acquisition, attachment, moral development , and the development of cognitive abilities.

Adolescent Development

Adolescence is a unique development period marked by physical changes, identity formation, and the development of independence. Researchers in this area examine issues like peer relationships, identity development, and risk-taking behavior.

Adult Development and Aging

This area explores how individuals change and adapt as they move through adulthood and into old age. Researchers study topics like cognitive aging, personality development, and the impact of life events on well-being.

Social and Emotional Development

This field focuses on how individuals develop social skills, emotions, and interpersonal relationships. It examines topics such as attachment theory, empathy, and social cognition.

Cognitive Development

Cognitive development refers to changes in thinking, problem-solving, and reasoning abilities across the lifespan. Researchers study cognitive processes like memory, problem-solving, and language development.

Developmental Disabilities

Some developmental psychologists specialize in studying and working with individuals with developmental disabilities, such as autism spectrum disorder or intellectual disabilities.

Developmental psychology is an interdisciplinary field that draws on research and theories from various domains, including biology, sociology, education, and neuroscience.

The ultimate goal of developmental psychology is to gain a deeper understanding of human growth and change processes, which can have practical applications in fields such as education, counseling, and healthcare.

Issues in Developmental Psychology

There have been several important debates and issues throughout the history of developmental psychology.

The three important developmental psychology issues focus on:

Continuity vs. Discontinuity

The continuity vs. discontinuity debate focuses on the processes through which development occurs, including whether development is a gradual process or occurs in a series of discrete stages.

Continuity suggests that development is a gradual process that takes place continually. On the other hand, discontinuity suggests that development follows a path that often involves abrupt changes during specific life stages.

Stage theories of development are examples of discontinuity. Such theories suggest that children go through the same developmental stages that follow a specific order and usually occur at certain ages.

Stability vs. Chan ge

Stability vs. change refers to the overall importance of early experiences versus later events.

Psychologists have also debated whether certain characteristics, such as personality traits, are largely stable throughout life or whether they develop and change as a result of experience.

The stability approach suggests that many characteristics are present or established during early childhood. The change approach proposes that experiences, including interactions with peers and parents, play the most significant role in development.

Nature vs. Nurture

The classic issue in child development research is the nature vs. nurture debate . Sometimes referred to as the nativism versus empiricism debate, it centers on whether genetic inheritance plays a larger role in influencing development and behavior or whether the environment has a stronger effect.

The nature versus nurture debate is a classic question in psychology that centers on whether genetics or environment plays a greater role in different aspects of human development and behavior.

In the past, nativists have argued that development is controlled almost entirely by genetic inheritance. Due to our shared DNA, certain aspects of development tend to follow a fairly predictable pattern in terms of timing and outcome. The onset of puberty, for example, tends to occur roughly around the same age.

As you might have already guessed, however, environmental factors can also play a role in development.

While empiricists may have argued that development was largely the result of environmental influences, experts today recognize that nature and nurture both have an important role to play and that the interaction between the two forces is also important.

In the case of puberty, genetics plays an important role in determining when it begins, but environmental factors such as receiving adequate nutrition are also critical.

Most psychologists recognize that both elements play an essential role, but the debate continues over many developmental questions about topics ranging from academic aptitude to personality traits.

History of Developmental Psychology

You might be surprised to learn that child development was once a topic of little concern. For much of human history, children were simply viewed as miniature versions of adults. It was not until after the Industrial Revolution that researchers began to recognize and investigate childhood as a unique, distinct, and important period of life.

Perhaps not surprisingly, some of the major theories of development center on the development that occurs during childhood. This is, after all, the time when developmental changes occur most rapidly.

Early investigations into child development began during the late 1800s with the work of naturalist Charles Darwin and physiologist Wilhelm Preyer. It was not until the 20th century with the work of famed psychologist Jean Piaget that concentrated research into child development theories began in earnest.

Other researchers who contributed a great deal of research during this period included Jean Bowlby, Lev Vygotsky, and Erik Erikson.

Developmental Psychology Theories

The modern study of developmental psychology did not emerge until relatively recently in history to address various aspects of how people change and grow over time. Some of these theories focus on how personality develops while others are centered on the cognitive changes that occur over the course of childhood.

Freud’s Developmental Psychology Theory

Freud’s theory of psychosexual development was an early theory that focused on how personality develops during early childhood . Sigmund Freud believed that psychosexual energy became focused on various erogenous zones at different points of development.

He also suggested that failing successfully to address the primary crisis of each stage could lead to a psychological fixation at that point of development.

Erikson’s Developmental Psychology Theory

Erikson’s theory of psychosocial development was similar to Freud’s in that it broke development down into stages and involved a type of developmental crisis during each stage.

Erikson’s theory was different however in that it looked at development throughout the entire course of life, from birth up until death.

Piaget’s Developmental Psychology Theory

Piaget’s theory of cognitive development suggested that there were fundamental differences in how children think versus how adults think. Piaget broke down this development into four distinct stages that typically occur at different stages of development.

The earliest stage is centered on gaining awareness of the self and the world, while later stages build on this knowledge as kids gain an increasingly sophisticated understanding of themselves, others, and the world around them.

Bowlby’s Developmental Psychology Theory

Bowlby’s attachment theory proposed that children are born predisposed to form attachments that aid in their protection, survival, nurturance, and development. Early patterns of attachment with caregivers can have an impact on how children fare as they age.

Those who can form secure attachments as children tend to grow up happier and healthier as adults.

Vygotsky’s Developmental Psychology Theory

Vygotsky’s sociocultural theory stressed the importance of social influences and culture on child cognitive development. While other theories such as Piaget’s suggest that there are universal stages of development, Vygotsky’s approach suggests that how kids learn varies depending upon the culture of their upbringing.

Goals of Developmental Psychology

Like other areas of psychology, the goals of developmental psychology are not only to describe how development occurs but also to explain, predict, and even control the course of development.

By better understanding the many influences contributing to normative development, psychologists can recommend strategies, approaches, and interventions that lead to better outcomes and healthier, happier children.

The Process of Normal Development

Developmental psychology seeks to understand both normal and abnormal development. To describe how children develop, researchers must note both the normative patterns that occur (i.e. how most kids develop) and individual differences (i.e. variations that may occur).

Making Predictions About Development

Predicting developmental events allows parents, teachers, psychologists, and healthcare providers to anticipate the needs of children and respond appropriately. This also applies to later stages of life.

Adults realize that they may face specific health issues that result from the aging process, which allows them to make lifestyle and behavioral changes today that will influence later health and development.

Making Positive Changes

Finally, developmental psychology allows experts to have an influence in the lives of children, adults, and elderly individuals. Understanding the developmental challenges that people face at different points in life makes it possible to design educational programs, public health initiatives, and targeted interventions designed to maximize well-being and overcome potential problems.

For example, developmental psychologists have found that social connections are important for cognitive and mental health later in life. As a result, communities can encourage such social activity by creating senior citizens centers where older adults can find connectivity and social support networks.

Impact of Developmental Psychology

Developmental psychology also significantly shapes how psychologists, educators, and health professionals approach various real-world problems. Developmental psychology can improve the lives of children and families by looking at issues affecting social issues, parenting concerns, educational practices, and physical and mental health.

Research on human development has significantly contributed to our understanding of the parenting approaches that lead to the most successful child outcomes.

For example, psychologist Diana Baumrind suggested that discipline approaches, warmth, communication styles, and parental expectations marked some essential dimensions of parenting.

Today, researchers often identify four distinct parenting styles characterized by how parents interact and nurture their children.

Experts believe the authoritative style, typified by high expectations, strong communication, warmth, and ample support, is the best approach to parenting children. Kids raised by authoritative parents tend to be happier, exhibit better self-regulation, and have stronger social skills.

Developmental psychology has provided a wealth of research on children’s cognitive growth, impacting instructional practices and strategies. Theories of constructivism, for example, have helped teachers and educational designers better understand how children actively construct meaning about the world around them.

Those working in health care fields are generally required to complete at least one course in developmental psychology as part of their education. By better understanding the basics of human development, healthcare providers can be better equipped to help their patients and improve health outcomes.

Neonatal nurses, for example, can use their understanding of infant health and safety to educate new parents about how to best care for their newborns. Those working with elderly patients can empathize with their psychological and physical concerns and provide services that contribute to the best possible palliative care as these individuals face serious health issues.

Developmental psychology is not just a topic of concern to psychologists and researchers, it is a topic that touches on many other fields ranging from education to healthcare. By discovering more about how children grow and how adults age, we can better understand people and the challenges they face at all stages of life.

Baumrind, D. (1967). Child care practices anteceding three patterns of preschool behavior. Genetic Psychology Monographs, 75(1), 43-88.

Erikson, E.H. (1963). Childhood and Society. (2nd ed.). New York: Norton.

Vygotsky, L.S. (1978). Mind in Society. Cambridge, MA: Harvard University Press.

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What Is Developmental Psychology?

Conditions treated, training and certifications.

Developmental psychology is the study of how humans grow, change, and adapt across the course of their lives. Developmental psychologists research the stages of physical, emotional, social, and intellectual development from the prenatal stage through infancy, childhood, adolescence, and adulthood.

This article covers developmental psychology, including the definition, types, life stages, and how to seek treatment when necessary.

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Defining Developmental Psychology

According to the American Psychological Association (APA), developmental psychology is a branch of psychology that focuses on how human beings grow, change, adapt, and mature across various life stages. Developmental psychology is also known as human development or lifespan psychology.

In each of the life stages of developmental psychology, people generally meet certain physical, emotional, and social milestones. These are the major life stages, according to developmental psychologists:

• Prenatal development: Developmental psychologists are interested in diagnoses, such as Down syndrome, that might be noticed during the prenatal (before birth) stage. They also investigate how maternal behaviors (behaviors of the pregnant parent), such as nutrition and drug use, could affect the developing fetus.
• Early childhood: Developmental psychologists are interested in whether young children are meeting key milestones, such as walking, talking, and developing fine motor skills (coordination in the hands, fingers, and wrists). They might also be interested in a child’s attachment to their parents and other caregivers.
• Middle childhood: In this stage, children learn about the world and acquire knowledge through experimentation, questioning, and observation. They begin to develop logical and moral reasoning skills.
• Adolescence: Adolescence is a time of major strides in terms of personal development and identity formation. Teens and young adults might experiment with various identities, career choices, or areas of interest.
• Early adulthood: During early adulthood, most people are focused on preparing for the rest of their lives through a focus on education, career, and financial independence. Romantic relationships, marriage, family-building, setting down “roots,” and child-rearing are often a focus of this life stage.
• Middle adulthood: Middle-aged adults are often focused on helping the next generation, whether in their own family or their community. They are also often interested in the legacy they’ll leave behind.
• Older adulthood: In addition to physical health challenges, older people might face issues like dementia or cognitive decline (decline in thinking, remembering, and reasoning). Older adults also often need to reflect on their lives, tell their stories, and find meaning and peace within the aging process.

The Origins of Developmental Psychology

During its early development as a branch of psychology in the late 19th and early 20th centuries, developmental psychology focused on infant and child development. As the field grew, so did its focus. Today, developmental psychologists focus on all stages of the human lifespan.  

Theories of Developmental Psychology

As developmental psychology grew over time, various researchers proposed theories about how to understand the process of human development. Depending on their training, a developmental psychologist might focus on a specific theory or approach within the field. 

These are a few of the major branches of developmental psychology.

Psychosocial Developmental Theory

Building on Austrian neurologist and the founder of psychoanalysis Sigmund Freud’s theory of psychosexual development , psychologist Erik Erikson proposed a lifespan theory that included eight stages of psychosocial development .

Each of the stages corresponds to both an age range and a core “crisis” (such as trust vs. mistrust in infancy) that must be resolved before someone can move on to the next.

Cognitive Developmental Theory

Swiss psychologist Jean Piaget’s theory of cognitive development focuses on how children and youth gradually become able to think logically and scientifically. Piaget proposed that cognition develops through four distinct stages of intellectual development, beginning at birth and ending at age 12.

Attachment Theory

Attachment theory , originally developed by psychoanalyst John Bowlby, establishes the importance of a supportive, steady, and loving caregiver in infant and child development. If a child doesn’t establish such a connection, or if they experience parental separation or loss, they might continue to struggle with healthy attachments as they get older.

Sociocultural Developmental Theory

While Bowlby considered the importance of the immediate family in child development, psychologist Lev Vygotsky’s sociocultural developmental theory looks at the role of society. Cultural influences and beliefs can have a profound impact on how a person views their own identity and relates to others.

Developmental psychologists can help people address developmental issues in order to reach their full potential. 

Some of the conditions a developmental psychologist might treat include:

• Learning disabilities
• Intellectual disabilities
• Developmental delays
• Motor skill delays
• Issues with social and emotional development
• Auditory processing (hearing) disorder
• Autism spectrum disorder (ASD)
• Speech and language delays
• Mental health conditions like anxiety and depression, especially related to life stages

The training required to become a developmental psychologist is similar to that in other subfields of psychology. Most developmental psychologists start with an undergraduate degree in psychology or a related field, followed by a master’s degree and a doctoral degree (PhD). 

There are many master’s, graduate certificate, and PhD programs in developmental psychology in the United States. Some focus on a certain part of a person's lifespan, such as child and adolescent development. In addition to research and teaching, graduates may participate in a practicum or internship to pursue licensing as a therapist. 

When to Seek Treatment

If you're concerned that your child is facing a developmental delay, a developmental psychologist can assess them to ensure that they are meeting their milestones. It's best to seek an assessment, diagnosis, and treatment early, so intervention can begin as soon as possible.

Examples of when to see a developmental psychologist may include:

• An infant is struggling to bond with their parents.
• A toddler is missing milestones, such as walking or developing speech.
• A school-aged child is not progressing appropriately in reading or writing.
• An adolescent is facing challenges related to social and/or emotional development.

A developmental psychologist might perform physical and/or cognitive testing to diagnose your child or refer them to another specialist, including the following:

• Physical therapist (helps people improve movement and manage pain)
• Occupational therapist (helps people adjust to everyday activities after injury, illness, or disability)
• Speech-language pathologist (treats speech, language, and social and cognitive communication)
• Psychotherapist (uses talk therapy to treat mental health conditions)
• Neurologist (medical doctor who treats disorders of the brain, spinal cord, and nerves)
• Psychiatrist (medical doctor specializing in mental health conditions)

A developmental psychologist will also likely ask you and your child questions about issues in areas of their life such as friends, behavior, or school performance.

In addition to working with infants and children, developmental psychologists can also help people at any stage of life. In particular, many older adults benefit from working with a developmental psychologist if they're experiencing symptoms of dementia, ill health, or cognitive decline.

Developmental psychology is the study of how human beings grow and change throughout their lives. Many developmental psychologists focus on the intellectual, social, emotional, and physical development of infants, children, and adolescents. Others treat and assess people of all ages. 

Developmental psychologists can treat issues such as developmental delays, intellectual disabilities, learning disabilities, speech and language delays, motor skill delays, dementia, anxiety, depression, auditory processing disorder, autism spectrum disorder, and more. They also make referrals to other specialists, such as physical therapists, psychiatrists, and speech-language pathologists. 

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By Laura Dorwart Dr. Dorwart has a Ph.D. from UC San Diego and is a health journalist interested in mental health, pregnancy, and disability rights.

Research Hypothesis In Psychology: Types, & Examples

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Editor-in-Chief for Simply Psychology

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Saul Mcleod, PhD., is a qualified psychology teacher with over 18 years of experience in further and higher education. He has been published in peer-reviewed journals, including the Journal of Clinical Psychology.

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A research hypothesis, in its plural form “hypotheses,” is a specific, testable prediction about the anticipated results of a study, established at its outset. It is a key component of the scientific method .

Hypotheses connect theory to data and guide the research process towards expanding scientific understanding

Some key points about hypotheses:

• A hypothesis expresses an expected pattern or relationship. It connects the variables under investigation.
• It is stated in clear, precise terms before any data collection or analysis occurs. This makes the hypothesis testable.
• A hypothesis must be falsifiable. It should be possible, even if unlikely in practice, to collect data that disconfirms rather than supports the hypothesis.
• Hypotheses guide research. Scientists design studies to explicitly evaluate hypotheses about how nature works.
• For a hypothesis to be valid, it must be testable against empirical evidence. The evidence can then confirm or disprove the testable predictions.
• Hypotheses are informed by background knowledge and observation, but go beyond what is already known to propose an explanation of how or why something occurs.

Predictions typically arise from a thorough knowledge of the research literature, curiosity about real-world problems or implications, and integrating this to advance theory. They build on existing literature while providing new insight.

Types of Research Hypotheses

Alternative hypothesis.

The research hypothesis is often called the alternative or experimental hypothesis in experimental research.

It typically suggests a potential relationship between two key variables: the independent variable, which the researcher manipulates, and the dependent variable, which is measured based on those changes.

The alternative hypothesis states a relationship exists between the two variables being studied (one variable affects the other).

A hypothesis is a testable statement or prediction about the relationship between two or more variables. It is a key component of the scientific method. Some key points about hypotheses:

• Important hypotheses lead to predictions that can be tested empirically. The evidence can then confirm or disprove the testable predictions.

In summary, a hypothesis is a precise, testable statement of what researchers expect to happen in a study and why. Hypotheses connect theory to data and guide the research process towards expanding scientific understanding.

An experimental hypothesis predicts what change(s) will occur in the dependent variable when the independent variable is manipulated.

It states that the results are not due to chance and are significant in supporting the theory being investigated.

The alternative hypothesis can be directional, indicating a specific direction of the effect, or non-directional, suggesting a difference without specifying its nature. It’s what researchers aim to support or demonstrate through their study.

Null Hypothesis

The null hypothesis states no relationship exists between the two variables being studied (one variable does not affect the other). There will be no changes in the dependent variable due to manipulating the independent variable.

It states results are due to chance and are not significant in supporting the idea being investigated.

The null hypothesis, positing no effect or relationship, is a foundational contrast to the research hypothesis in scientific inquiry. It establishes a baseline for statistical testing, promoting objectivity by initiating research from a neutral stance.

Many statistical methods are tailored to test the null hypothesis, determining the likelihood of observed results if no true effect exists.

This dual-hypothesis approach provides clarity, ensuring that research intentions are explicit, and fosters consistency across scientific studies, enhancing the standardization and interpretability of research outcomes.

Nondirectional Hypothesis

A non-directional hypothesis, also known as a two-tailed hypothesis, predicts that there is a difference or relationship between two variables but does not specify the direction of this relationship.

It merely indicates that a change or effect will occur without predicting which group will have higher or lower values.

For example, “There is a difference in performance between Group A and Group B” is a non-directional hypothesis.

Directional Hypothesis

A directional (one-tailed) hypothesis predicts the nature of the effect of the independent variable on the dependent variable. It predicts in which direction the change will take place. (i.e., greater, smaller, less, more)

It specifies whether one variable is greater, lesser, or different from another, rather than just indicating that there’s a difference without specifying its nature.

For example, “Exercise increases weight loss” is a directional hypothesis.

Falsifiability

The Falsification Principle, proposed by Karl Popper , is a way of demarcating science from non-science. It suggests that for a theory or hypothesis to be considered scientific, it must be testable and irrefutable.

Falsifiability emphasizes that scientific claims shouldn’t just be confirmable but should also have the potential to be proven wrong.

It means that there should exist some potential evidence or experiment that could prove the proposition false.

However many confirming instances exist for a theory, it only takes one counter observation to falsify it. For example, the hypothesis that “all swans are white,” can be falsified by observing a black swan.

For Popper, science should attempt to disprove a theory rather than attempt to continually provide evidence to support a research hypothesis.

Can a Hypothesis be Proven?

Hypotheses make probabilistic predictions. They state the expected outcome if a particular relationship exists. However, a study result supporting a hypothesis does not definitively prove it is true.

All studies have limitations. There may be unknown confounding factors or issues that limit the certainty of conclusions. Additional studies may yield different results.

In science, hypotheses can realistically only be supported with some degree of confidence, not proven. The process of science is to incrementally accumulate evidence for and against hypothesized relationships in an ongoing pursuit of better models and explanations that best fit the empirical data. But hypotheses remain open to revision and rejection if that is where the evidence leads.

• Disproving a hypothesis is definitive. Solid disconfirmatory evidence will falsify a hypothesis and require altering or discarding it based on the evidence.
• However, confirming evidence is always open to revision. Other explanations may account for the same results, and additional or contradictory evidence may emerge over time.

We can never 100% prove the alternative hypothesis. Instead, we see if we can disprove, or reject the null hypothesis.

If we reject the null hypothesis, this doesn’t mean that our alternative hypothesis is correct but does support the alternative/experimental hypothesis.

Upon analysis of the results, an alternative hypothesis can be rejected or supported, but it can never be proven to be correct. We must avoid any reference to results proving a theory as this implies 100% certainty, and there is always a chance that evidence may exist which could refute a theory.

How to Write a Hypothesis

• Identify variables . The researcher manipulates the independent variable and the dependent variable is the measured outcome.
• Operationalized the variables being investigated . Operationalization of a hypothesis refers to the process of making the variables physically measurable or testable, e.g. if you are about to study aggression, you might count the number of punches given by participants.
• Decide on a direction for your prediction . If there is evidence in the literature to support a specific effect of the independent variable on the dependent variable, write a directional (one-tailed) hypothesis. If there are limited or ambiguous findings in the literature regarding the effect of the independent variable on the dependent variable, write a non-directional (two-tailed) hypothesis.
• Make it Testable : Ensure your hypothesis can be tested through experimentation or observation. It should be possible to prove it false (principle of falsifiability).
• Clear & concise language . A strong hypothesis is concise (typically one to two sentences long), and formulated using clear and straightforward language, ensuring it’s easily understood and testable.

Consider a hypothesis many teachers might subscribe to: students work better on Monday morning than on Friday afternoon (IV=Day, DV= Standard of work).

Now, if we decide to study this by giving the same group of students a lesson on a Monday morning and a Friday afternoon and then measuring their immediate recall of the material covered in each session, we would end up with the following:

• The alternative hypothesis states that students will recall significantly more information on a Monday morning than on a Friday afternoon.
• The null hypothesis states that there will be no significant difference in the amount recalled on a Monday morning compared to a Friday afternoon. Any difference will be due to chance or confounding factors.

More Examples

• Memory : Participants exposed to classical music during study sessions will recall more items from a list than those who studied in silence.
• Social Psychology : Individuals who frequently engage in social media use will report higher levels of perceived social isolation compared to those who use it infrequently.
• Developmental Psychology : Children who engage in regular imaginative play have better problem-solving skills than those who don’t.
• Clinical Psychology : Cognitive-behavioral therapy will be more effective in reducing symptoms of anxiety over a 6-month period compared to traditional talk therapy.
• Cognitive Psychology : Individuals who multitask between various electronic devices will have shorter attention spans on focused tasks than those who single-task.
• Health Psychology : Patients who practice mindfulness meditation will experience lower levels of chronic pain compared to those who don’t meditate.
• Organizational Psychology : Employees in open-plan offices will report higher levels of stress than those in private offices.
• Behavioral Psychology : Rats rewarded with food after pressing a lever will press it more frequently than rats who receive no reward.

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Developmental Psychology Research Methods

Kendra Cherry, MS, is a psychosocial rehabilitation specialist, psychology educator, and author of the "Everything Psychology Book."

Emily is a board-certified science editor who has worked with top digital publishing brands like Voices for Biodiversity, Study.com, GoodTherapy, Vox, and Verywell.

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Cross-Sectional Research Methods

Longitudinal research methods, correlational research methods, experimental research methods.

There are many different developmental psychology research methods, including cross-sectional, longitudinal, correlational, and experimental. Each has its own specific advantages and disadvantages. The one that a scientist chooses depends largely on the aim of the study and the nature of the phenomenon being studied.

Research design provides a standardized framework to test a hypothesis and evaluate whether the hypothesis is correct, incorrect, or inconclusive. Even if the hypothesis is untrue, the research can often provide insights that may prove valuable or move research in an entirely new direction.

At a Glance

In order to study developmental psychology, researchers utilize a number of different research methods. Some involve looking at different cross-sections of a population, while others look at how participants change over time. In other cases, researchers look at how whether certain variables appear to have a relationship with one another. In order to determine if there is a cause-and-effect relationship, however, psychologists much conduct experimental research.

Learn more about each of these different types of developmental psychology research methods, including when they are used and what they can reveal about human development.

Cross-sectional research involves looking at different groups of people with specific characteristics.

For example, a researcher might evaluate a group of young adults and compare the corresponding data from a group of older adults.

The benefit of this type of research is that it can be done relatively quickly; the research data is gathered at the same point in time. The disadvantage is that the research aims to make a direct association between a cause and an effect. This is not always so easy. In some cases, there may be confounding factors that contribute to the effect.

To this end, a cross-sectional study can suggest the odds of an effect occurring both in terms of the absolute risk (the odds of something happening over a period of time) and the relative risk (the odds of something happening in one group compared to another).  

Longitudinal research involves studying the same group of individuals over an extended period of time.

Data is collected at the outset of the study and gathered repeatedly through the course of study. In some cases, longitudinal studies can last for several decades or be open-ended. One such example is the Terman Study of the Gifted , which began in the 1920s and followed 1528 children for over 80 years.

The benefit of this longitudinal research is that it allows researchers to look at changes over time. By contrast, one of the obvious disadvantages is cost. Because of the expense of a long-term study, they tend to be confined to a smaller group of subjects or a narrower field of observation.

Challenges of Longitudinal Research

While revealing, longitudinal studies present a few challenges that make them more difficult to use when studying developmental psychology and other topics.

• Longitudinal studies are difficult to apply to a larger population.
• Another problem is that the participants can often drop out mid-study, shrinking the sample size and relative conclusions.
• Moreover, if certain outside forces change during the course of the study (including economics, politics, and science), they can influence the outcomes in a way that significantly skews the results.

For example, in Lewis Terman's longitudinal study, the correlation between IQ and achievement was blunted by such confounding forces as the Great Depression and World War II (which limited educational attainment) and gender politics of the 1940s and 1950s (which limited a woman's professional prospects).

Correlational research aims to determine if one variable has a measurable association with another.

In this type of non-experimental study, researchers look at relationships between the two variables but do not introduce the variables themselves. Instead, they gather and evaluate the available data and offer a statistical conclusion.

For example, the researchers may look at whether academic success in elementary school leads to better-paying jobs in the future. While the researchers can collect and evaluate the data, they do not manipulate any of the variables in question.

A correlational study can be appropriate and helpful if you cannot manipulate a variable because it is impossible, impractical, or unethical.

For example, imagine that a researcher wants to determine if living in a noisy environment makes people less efficient in the workplace. It would be impractical and unreasonable to artificially inflate the noise level in a working environment. Instead, researchers might collect data and then look for correlations between the variables of interest.

Limitations of Correlational Research

Correlational research has its limitations. While it can identify an association, it does not necessarily suggest a cause for the effect. Just because two variables have a relationship does not mean that changes in one will affect a change in the other.

Unlike correlational research, experimentation involves both the manipulation and measurement of variables . This model of research is the most scientifically conclusive and commonly used in medicine, chemistry, psychology, biology, and sociology.

Experimental research uses manipulation to understand cause and effect in a sampling of subjects. The sample is comprised of two groups: an experimental group in whom the variable (such as a drug or treatment) is introduced and a control group in whom the variable is not introduced.

Deciding the sample groups can be done in a number of ways:

• Population sampling, in which the subjects represent a specific population
• Random selection , in which subjects are chosen randomly to see if the effects of the variable are consistently achieved

Challenges in Experimental Resarch

While the statistical value of an experimental study is robust, it may be affected by confirmation bias . This is when the investigator's desire to publish or achieve an unambiguous result can skew the interpretations, leading to a false-positive conclusion.

One way to avoid this is to conduct a double-blind study in which neither the participants nor researchers are aware of which group is the control. A double-blind randomized controlled trial (RCT) is considered the gold standard of research.

What This Means For You

There are many different types of research methods that scientists use to study developmental psychology and other areas. Knowing more about how each of these methods works can give you a better understanding of what the findings of psychological research might mean for you.

Capili B. Cross-sectional studies .  Am J Nurs . 2021;121(10):59-62. doi:10.1097/01.NAJ.0000794280.73744.fe

Kesmodel US. Cross-sectional studies - what are they good for? .  Acta Obstet Gynecol Scand . 2018;97(4):388–393. doi:10.1111/aogs.13331

Noordzij M, van Diepen M, Caskey FC, Jager KJ. Relative risk versus absolute risk: One cannot be interpreted without the other . Nephrology Dialysis Transplantation. 2017;32(S2):ii13-ii18. doi:10.1093/ndt/gfw465

Kell HJ, Wai J. Terman Study of the Gifted . In: Frey B, ed.  The SAGE Encyclopedia of Educational Research, Measurement, and Evaluation . Vol. 4. Thousand Oaks, CA: SAGE Publications, Inc.; 2018. doi:10.4135/9781506326139.n691

Curtis EA, Comiskey C, Dempsey O. Importance and use of correlational research .  Nurse Res . 2016;23(6):20–25. doi:10.7748/nr.2016.e1382

Misra S.  Randomized double blind placebo control studies, the "Gold Standard" in intervention based studies .  Indian J Sex Transm Dis AIDS . 2012;33(2):131-4. doi:10.4103/2589-0557.102130

By Kendra Cherry, MSEd Kendra Cherry, MS, is a psychosocial rehabilitation specialist, psychology educator, and author of the "Everything Psychology Book."

2.4 Developing a Hypothesis

Learning objectives.

• Distinguish between a theory and a hypothesis.
• Discover how theories are used to generate hypotheses and how the results of studies can be used to further inform theories.
• Understand the characteristics of a good hypothesis.

Theories and Hypotheses

Before describing how to develop a hypothesis it is imporant to distinguish betwee a theory and a hypothesis. A  theory  is a coherent explanation or interpretation of one or more phenomena. Although theories can take a variety of forms, one thing they have in common is that they go beyond the phenomena they explain by including variables, structures, processes, functions, or organizing principles that have not been observed directly. Consider, for example, Zajonc’s theory of social facilitation and social inhibition. He proposed that being watched by others while performing a task creates a general state of physiological arousal, which increases the likelihood of the dominant (most likely) response. So for highly practiced tasks, being watched increases the tendency to make correct responses, but for relatively unpracticed tasks, being watched increases the tendency to make incorrect responses. Notice that this theory—which has come to be called drive theory—provides an explanation of both social facilitation and social inhibition that goes beyond the phenomena themselves by including concepts such as “arousal” and “dominant response,” along with processes such as the effect of arousal on the dominant response.

Outside of science, referring to an idea as a theory often implies that it is untested—perhaps no more than a wild guess. In science, however, the term theory has no such implication. A theory is simply an explanation or interpretation of a set of phenomena. It can be untested, but it can also be extensively tested, well supported, and accepted as an accurate description of the world by the scientific community. The theory of evolution by natural selection, for example, is a theory because it is an explanation of the diversity of life on earth—not because it is untested or unsupported by scientific research. On the contrary, the evidence for this theory is overwhelmingly positive and nearly all scientists accept its basic assumptions as accurate. Similarly, the “germ theory” of disease is a theory because it is an explanation of the origin of various diseases, not because there is any doubt that many diseases are caused by microorganisms that infect the body.

A  hypothesis , on the other hand, is a specific prediction about a new phenomenon that should be observed if a particular theory is accurate. It is an explanation that relies on just a few key concepts. Hypotheses are often specific predictions about what will happen in a particular study. They are developed by considering existing evidence and using reasoning to infer what will happen in the specific context of interest. Hypotheses are often but not always derived from theories. So a hypothesis is often a prediction based on a theory but some hypotheses are a-theoretical and only after a set of observations have been made, is a theory developed. This is because theories are broad in nature and they explain larger bodies of data. So if our research question is really original then we may need to collect some data and make some observation before we can develop a broader theory.

Theories and hypotheses always have this  if-then  relationship. “ If   drive theory is correct,  then  cockroaches should run through a straight runway faster, and a branching runway more slowly, when other cockroaches are present.” Although hypotheses are usually expressed as statements, they can always be rephrased as questions. “Do cockroaches run through a straight runway faster when other cockroaches are present?” Thus deriving hypotheses from theories is an excellent way of generating interesting research questions.

But how do researchers derive hypotheses from theories? One way is to generate a research question using the techniques discussed in this chapter  and then ask whether any theory implies an answer to that question. For example, you might wonder whether expressive writing about positive experiences improves health as much as expressive writing about traumatic experiences. Although this  question  is an interesting one  on its own, you might then ask whether the habituation theory—the idea that expressive writing causes people to habituate to negative thoughts and feelings—implies an answer. In this case, it seems clear that if the habituation theory is correct, then expressive writing about positive experiences should not be effective because it would not cause people to habituate to negative thoughts and feelings. A second way to derive hypotheses from theories is to focus on some component of the theory that has not yet been directly observed. For example, a researcher could focus on the process of habituation—perhaps hypothesizing that people should show fewer signs of emotional distress with each new writing session.

Among the very best hypotheses are those that distinguish between competing theories. For example, Norbert Schwarz and his colleagues considered two theories of how people make judgments about themselves, such as how assertive they are (Schwarz et al., 1991) [1] . Both theories held that such judgments are based on relevant examples that people bring to mind. However, one theory was that people base their judgments on the  number  of examples they bring to mind and the other was that people base their judgments on how  easily  they bring those examples to mind. To test these theories, the researchers asked people to recall either six times when they were assertive (which is easy for most people) or 12 times (which is difficult for most people). Then they asked them to judge their own assertiveness. Note that the number-of-examples theory implies that people who recalled 12 examples should judge themselves to be more assertive because they recalled more examples, but the ease-of-examples theory implies that participants who recalled six examples should judge themselves as more assertive because recalling the examples was easier. Thus the two theories made opposite predictions so that only one of the predictions could be confirmed. The surprising result was that participants who recalled fewer examples judged themselves to be more assertive—providing particularly convincing evidence in favor of the ease-of-retrieval theory over the number-of-examples theory.

Theory Testing

The primary way that scientific researchers use theories is sometimes called the hypothetico-deductive method  (although this term is much more likely to be used by philosophers of science than by scientists themselves). A researcher begins with a set of phenomena and either constructs a theory to explain or interpret them or chooses an existing theory to work with. He or she then makes a prediction about some new phenomenon that should be observed if the theory is correct. Again, this prediction is called a hypothesis. The researcher then conducts an empirical study to test the hypothesis. Finally, he or she reevaluates the theory in light of the new results and revises it if necessary. This process is usually conceptualized as a cycle because the researcher can then derive a new hypothesis from the revised theory, conduct a new empirical study to test the hypothesis, and so on. As  Figure 2.2  shows, this approach meshes nicely with the model of scientific research in psychology presented earlier in the textbook—creating a more detailed model of “theoretically motivated” or “theory-driven” research.

Figure 2.2 Hypothetico-Deductive Method Combined With the General Model of Scientific Research in Psychology Together they form a model of theoretically motivated research.

As an example, let us consider Zajonc’s research on social facilitation and inhibition. He started with a somewhat contradictory pattern of results from the research literature. He then constructed his drive theory, according to which being watched by others while performing a task causes physiological arousal, which increases an organism’s tendency to make the dominant response. This theory predicts social facilitation for well-learned tasks and social inhibition for poorly learned tasks. He now had a theory that organized previous results in a meaningful way—but he still needed to test it. He hypothesized that if his theory was correct, he should observe that the presence of others improves performance in a simple laboratory task but inhibits performance in a difficult version of the very same laboratory task. To test this hypothesis, one of the studies he conducted used cockroaches as subjects (Zajonc, Heingartner, & Herman, 1969) [2] . The cockroaches ran either down a straight runway (an easy task for a cockroach) or through a cross-shaped maze (a difficult task for a cockroach) to escape into a dark chamber when a light was shined on them. They did this either while alone or in the presence of other cockroaches in clear plastic “audience boxes.” Zajonc found that cockroaches in the straight runway reached their goal more quickly in the presence of other cockroaches, but cockroaches in the cross-shaped maze reached their goal more slowly when they were in the presence of other cockroaches. Thus he confirmed his hypothesis and provided support for his drive theory. (Zajonc also showed that drive theory existed in humans (Zajonc & Sales, 1966) [3] in many other studies afterward).

Incorporating Theory into Your Research

When you write your research report or plan your presentation, be aware that there are two basic ways that researchers usually include theory. The first is to raise a research question, answer that question by conducting a new study, and then offer one or more theories (usually more) to explain or interpret the results. This format works well for applied research questions and for research questions that existing theories do not address. The second way is to describe one or more existing theories, derive a hypothesis from one of those theories, test the hypothesis in a new study, and finally reevaluate the theory. This format works well when there is an existing theory that addresses the research question—especially if the resulting hypothesis is surprising or conflicts with a hypothesis derived from a different theory.

To use theories in your research will not only give you guidance in coming up with experiment ideas and possible projects, but it lends legitimacy to your work. Psychologists have been interested in a variety of human behaviors and have developed many theories along the way. Using established theories will help you break new ground as a researcher, not limit you from developing your own ideas.

Characteristics of a Good Hypothesis

There are three general characteristics of a good hypothesis. First, a good hypothesis must be testable and falsifiable . We must be able to test the hypothesis using the methods of science and if you’ll recall Popper’s falsifiability criterion, it must be possible to gather evidence that will disconfirm the hypothesis if it is indeed false. Second, a good hypothesis must be  logical. As described above, hypotheses are more than just a random guess. Hypotheses should be informed by previous theories or observations and logical reasoning. Typically, we begin with a broad and general theory and use  deductive reasoning to generate a more specific hypothesis to test based on that theory. Occasionally, however, when there is no theory to inform our hypothesis, we use  inductive reasoning  which involves using specific observations or research findings to form a more general hypothesis. Finally, the hypothesis should be  positive.  That is, the hypothesis should make a positive statement about the existence of a relationship or effect, rather than a statement that a relationship or effect does not exist. As scientists, we don’t set out to show that relationships do not exist or that effects do not occur so our hypotheses should not be worded in a way to suggest that an effect or relationship does not exist. The nature of science is to assume that something does not exist and then seek to find evidence to prove this wrong, to show that really it does exist. That may seem backward to you but that is the nature of the scientific method. The underlying reason for this is beyond the scope of this chapter but it has to do with statistical theory.

Key Takeaways

• A theory is broad in nature and explains larger bodies of data. A hypothesis is more specific and makes a prediction about the outcome of a particular study.
• Working with theories is not “icing on the cake.” It is a basic ingredient of psychological research.
• Like other scientists, psychologists use the hypothetico-deductive method. They construct theories to explain or interpret phenomena (or work with existing theories), derive hypotheses from their theories, test the hypotheses, and then reevaluate the theories in light of the new results.
• Practice: Find a recent empirical research report in a professional journal. Read the introduction and highlight in different colors descriptions of theories and hypotheses.
• Schwarz, N., Bless, H., Strack, F., Klumpp, G., Rittenauer-Schatka, H., & Simons, A. (1991). Ease of retrieval as information: Another look at the availability heuristic.  Journal of Personality and Social Psychology, 61 , 195–202. ↵
• Zajonc, R. B., Heingartner, A., & Herman, E. M. (1969). Social enhancement and impairment of performance in the cockroach.  Journal of Personality and Social Psychology, 13 , 83–92. ↵
• Zajonc, R.B. & Sales, S.M. (1966). Social facilitation of dominant and subordinate responses. Journal of Experimental Social Psychology, 2 , 160-168. ↵

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Developing a Hypothesis

Rajiv S. Jhangiani; I-Chant A. Chiang; Carrie Cuttler; and Dana C. Leighton

Learning Objectives

• Distinguish between a theory and a hypothesis.
• Discover how theories are used to generate hypotheses and how the results of studies can be used to further inform theories.
• Understand the characteristics of a good hypothesis.

Theories and Hypotheses

Before describing how to develop a hypothesis, it is important to distinguish between a theory and a hypothesis. A  theory  is a coherent explanation or interpretation of one or more phenomena. Although theories can take a variety of forms, one thing they have in common is that they go beyond the phenomena they explain by including variables, structures, processes, functions, or organizing principles that have not been observed directly. Consider, for example, Zajonc’s theory of social facilitation and social inhibition (1965) [1] . He proposed that being watched by others while performing a task creates a general state of physiological arousal, which increases the likelihood of the dominant (most likely) response. So for highly practiced tasks, being watched increases the tendency to make correct responses, but for relatively unpracticed tasks, being watched increases the tendency to make incorrect responses. Notice that this theory—which has come to be called drive theory—provides an explanation of both social facilitation and social inhibition that goes beyond the phenomena themselves by including concepts such as “arousal” and “dominant response,” along with processes such as the effect of arousal on the dominant response.

Outside of science, referring to an idea as a theory often implies that it is untested—perhaps no more than a wild guess. In science, however, the term theory has no such implication. A theory is simply an explanation or interpretation of a set of phenomena. It can be untested, but it can also be extensively tested, well supported, and accepted as an accurate description of the world by the scientific community. The theory of evolution by natural selection, for example, is a theory because it is an explanation of the diversity of life on earth—not because it is untested or unsupported by scientific research. On the contrary, the evidence for this theory is overwhelmingly positive and nearly all scientists accept its basic assumptions as accurate. Similarly, the “germ theory” of disease is a theory because it is an explanation of the origin of various diseases, not because there is any doubt that many diseases are caused by microorganisms that infect the body.

A  hypothesis , on the other hand, is a specific prediction about a new phenomenon that should be observed if a particular theory is accurate. It is an explanation that relies on just a few key concepts. Hypotheses are often specific predictions about what will happen in a particular study. They are developed by considering existing evidence and using reasoning to infer what will happen in the specific context of interest. Hypotheses are often but not always derived from theories. So a hypothesis is often a prediction based on a theory but some hypotheses are a-theoretical and only after a set of observations have been made, is a theory developed. This is because theories are broad in nature and they explain larger bodies of data. So if our research question is really original then we may need to collect some data and make some observations before we can develop a broader theory.

Theories and hypotheses always have this  if-then  relationship. “ If   drive theory is correct,  then  cockroaches should run through a straight runway faster, and a branching runway more slowly, when other cockroaches are present.” Although hypotheses are usually expressed as statements, they can always be rephrased as questions. “Do cockroaches run through a straight runway faster when other cockroaches are present?” Thus deriving hypotheses from theories is an excellent way of generating interesting research questions.

But how do researchers derive hypotheses from theories? One way is to generate a research question using the techniques discussed in this chapter  and then ask whether any theory implies an answer to that question. For example, you might wonder whether expressive writing about positive experiences improves health as much as expressive writing about traumatic experiences. Although this  question  is an interesting one  on its own, you might then ask whether the habituation theory—the idea that expressive writing causes people to habituate to negative thoughts and feelings—implies an answer. In this case, it seems clear that if the habituation theory is correct, then expressive writing about positive experiences should not be effective because it would not cause people to habituate to negative thoughts and feelings. A second way to derive hypotheses from theories is to focus on some component of the theory that has not yet been directly observed. For example, a researcher could focus on the process of habituation—perhaps hypothesizing that people should show fewer signs of emotional distress with each new writing session.

Among the very best hypotheses are those that distinguish between competing theories. For example, Norbert Schwarz and his colleagues considered two theories of how people make judgments about themselves, such as how assertive they are (Schwarz et al., 1991) [2] . Both theories held that such judgments are based on relevant examples that people bring to mind. However, one theory was that people base their judgments on the  number  of examples they bring to mind and the other was that people base their judgments on how  easily  they bring those examples to mind. To test these theories, the researchers asked people to recall either six times when they were assertive (which is easy for most people) or 12 times (which is difficult for most people). Then they asked them to judge their own assertiveness. Note that the number-of-examples theory implies that people who recalled 12 examples should judge themselves to be more assertive because they recalled more examples, but the ease-of-examples theory implies that participants who recalled six examples should judge themselves as more assertive because recalling the examples was easier. Thus the two theories made opposite predictions so that only one of the predictions could be confirmed. The surprising result was that participants who recalled fewer examples judged themselves to be more assertive—providing particularly convincing evidence in favor of the ease-of-retrieval theory over the number-of-examples theory.

Theory Testing

The primary way that scientific researchers use theories is sometimes called the hypothetico-deductive method  (although this term is much more likely to be used by philosophers of science than by scientists themselves). Researchers begin with a set of phenomena and either construct a theory to explain or interpret them or choose an existing theory to work with. They then make a prediction about some new phenomenon that should be observed if the theory is correct. Again, this prediction is called a hypothesis. The researchers then conduct an empirical study to test the hypothesis. Finally, they reevaluate the theory in light of the new results and revise it if necessary. This process is usually conceptualized as a cycle because the researchers can then derive a new hypothesis from the revised theory, conduct a new empirical study to test the hypothesis, and so on. As  Figure 2.3  shows, this approach meshes nicely with the model of scientific research in psychology presented earlier in the textbook—creating a more detailed model of “theoretically motivated” or “theory-driven” research.

As an example, let us consider Zajonc’s research on social facilitation and inhibition. He started with a somewhat contradictory pattern of results from the research literature. He then constructed his drive theory, according to which being watched by others while performing a task causes physiological arousal, which increases an organism’s tendency to make the dominant response. This theory predicts social facilitation for well-learned tasks and social inhibition for poorly learned tasks. He now had a theory that organized previous results in a meaningful way—but he still needed to test it. He hypothesized that if his theory was correct, he should observe that the presence of others improves performance in a simple laboratory task but inhibits performance in a difficult version of the very same laboratory task. To test this hypothesis, one of the studies he conducted used cockroaches as subjects (Zajonc, Heingartner, & Herman, 1969) [3] . The cockroaches ran either down a straight runway (an easy task for a cockroach) or through a cross-shaped maze (a difficult task for a cockroach) to escape into a dark chamber when a light was shined on them. They did this either while alone or in the presence of other cockroaches in clear plastic “audience boxes.” Zajonc found that cockroaches in the straight runway reached their goal more quickly in the presence of other cockroaches, but cockroaches in the cross-shaped maze reached their goal more slowly when they were in the presence of other cockroaches. Thus he confirmed his hypothesis and provided support for his drive theory. (Zajonc also showed that drive theory existed in humans [Zajonc & Sales, 1966] [4] in many other studies afterward).

Incorporating Theory into Your Research

When you write your research report or plan your presentation, be aware that there are two basic ways that researchers usually include theory. The first is to raise a research question, answer that question by conducting a new study, and then offer one or more theories (usually more) to explain or interpret the results. This format works well for applied research questions and for research questions that existing theories do not address. The second way is to describe one or more existing theories, derive a hypothesis from one of those theories, test the hypothesis in a new study, and finally reevaluate the theory. This format works well when there is an existing theory that addresses the research question—especially if the resulting hypothesis is surprising or conflicts with a hypothesis derived from a different theory.

To use theories in your research will not only give you guidance in coming up with experiment ideas and possible projects, but it lends legitimacy to your work. Psychologists have been interested in a variety of human behaviors and have developed many theories along the way. Using established theories will help you break new ground as a researcher, not limit you from developing your own ideas.

Characteristics of a Good Hypothesis

There are three general characteristics of a good hypothesis. First, a good hypothesis must be testable and falsifiable . We must be able to test the hypothesis using the methods of science and if you’ll recall Popper’s falsifiability criterion, it must be possible to gather evidence that will disconfirm the hypothesis if it is indeed false. Second, a good hypothesis must be logical. As described above, hypotheses are more than just a random guess. Hypotheses should be informed by previous theories or observations and logical reasoning. Typically, we begin with a broad and general theory and use  deductive reasoning to generate a more specific hypothesis to test based on that theory. Occasionally, however, when there is no theory to inform our hypothesis, we use  inductive reasoning  which involves using specific observations or research findings to form a more general hypothesis. Finally, the hypothesis should be positive. That is, the hypothesis should make a positive statement about the existence of a relationship or effect, rather than a statement that a relationship or effect does not exist. As scientists, we don’t set out to show that relationships do not exist or that effects do not occur so our hypotheses should not be worded in a way to suggest that an effect or relationship does not exist. The nature of science is to assume that something does not exist and then seek to find evidence to prove this wrong, to show that it really does exist. That may seem backward to you but that is the nature of the scientific method. The underlying reason for this is beyond the scope of this chapter but it has to do with statistical theory.

• Zajonc, R. B. (1965). Social facilitation.  Science, 149 , 269–274 ↵
• Schwarz, N., Bless, H., Strack, F., Klumpp, G., Rittenauer-Schatka, H., & Simons, A. (1991). Ease of retrieval as information: Another look at the availability heuristic.  Journal of Personality and Social Psychology, 61 , 195–202. ↵
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A coherent explanation or interpretation of one or more phenomena.

A specific prediction about a new phenomenon that should be observed if a particular theory is accurate.

A cyclical process of theory development, starting with an observed phenomenon, then developing or using a theory to make a specific prediction of what should happen if that theory is correct, testing that prediction, refining the theory in light of the findings, and using that refined theory to develop new hypotheses, and so on.

The ability to test the hypothesis using the methods of science and the possibility to gather evidence that will disconfirm the hypothesis if it is indeed false.

Developing a Hypothesis Copyright © 2022 by Rajiv S. Jhangiani; I-Chant A. Chiang; Carrie Cuttler; and Dana C. Leighton is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License , except where otherwise noted.

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Developmental Psychology Studies: 10 Examples

Discover ten classic developmental psychology experiments that study how children’s self, memory, language, learning and more emerge.

Once upon a time, although it seems barely credible to us now, we were all children.

We gurgled, we cried, we laughed, we explored, we fell down, and we had very little idea about the journey on which we had just embarked.

Barring mishap, over the first few years of our lives we developed memory, language, self-concept, cognitive, social and emotional abilities.

We took our first steps towards our future selves.

Child psychology — or, more broadly, developmental psychology — is not just the study of children, it is the study of you and me and how we came to be this way.

Just as discovering your history can teach you about the future, so developmental psychology shows us what we once were and even what we will become.

Here are 10 classic developmental psychology studies that have illuminated crucial areas of childhood development.

Each one is a piece in the jigsaw puzzle that is ourselves, and each one reminds us, through examining just one piece, how aspects of experience we now take for granted were once so complex.

Click the links for a more extensive description of each developmental psychology experiment.

1. Infant memory develops very early on

Some argue it’s impossible for us to remember anything much from before around two to four years of age.

Others think our memories can go way back – perhaps even to before birth.

The question of infant memory is thorny because it’s hard to test whether adults’ earliest memories are real or imagined.

What psychologists have done, though, is examine the emergence of memory in our first few years with a series of now classic experiments in developmental psychology.

These have found that our memory systems actually work quite well from very early on.

Infants’ memories also seems to work in much the same way as adult memories – it’s just that infant memories are much more fragile.

2. Developmental psychology: when the self emerges

To this day the ‘mirror test’ remains the best developmental psychology experiment yet developed for examining the emergence of self-concept in infants using the mirror test .

Most people look out for number one, themselves, which makes it strange to think that there was ever a time when we had no concept of ‘me’.

A simple study dating from the early 70s suggests that before the age of around two years old we can’t recognise ourselves in the mirror.

Because of this study, and the many variations in developmental psychology that have followed, some claim that it isn’t until our second birthday that our self-concept emerges.

3. How children learn

A classic study of childhood learning suggests true understanding comes from letting go of established preconceptions.

How children revise their understanding of the world is one of the most fascinating areas of developmental psychology.

But it is not just relevant to children; we all have to take on new concepts from time-to-time – even though they may not be as profound as the origin of the species.

It’s tempting to think that learning is largely about memory – especially since in the bad old days of education learning was largely accomplished by rote.

However, the idea of ‘mental models’ suggests children create, and then test, mental models of the way the world works in order to build up our understanding, and that is how children learn.

4. Attachment styles in developmental psychology

Attachment styles analyse how people respond to threats and problems in their personal relationships.

People who find relationships difficult often become unable to participate in the ordinary give-and-take of everyday life.

They may become hostile towards others, have problems in education as well as a greater chance of developing psychiatric disorders later in life.

These difficulties sometimes have their roots in the most important early relationships, evidenced in attachment styles.

It’s no wonder that developmental psychologists are so interested in the first relationships we build with our primary caregivers.

These attachment styles are likely to prove a vital influence on all our future relationships, including those with our spouse, our workmates and our own children.

While you can’t blame everything on your parents, early relationship attachment styles are like a template that we take forward with us in life.

5. Infants imitate others when only weeks old

One of the most basic forms of social behaviour is copying another person.

Although imitation is something we adults take for granted, it’s actually a pretty demanding process for a young infant.

At the heart of imitation is understanding the difference between yourself and others – something that famous Swiss child psychologist Jean Piaget thought didn’t emerge immediately in infants.

Consequently, he argued that infants could not imitate others until they were 8 to 12 months of age.

However, now some researchers think tiny infants who are between 12- and 21-days-old can imitate others.

6. When children can simulate other minds

Theory of mind is when we can put ourselves in other people’s shoes to try and imagine their thoughts, intentions and possible actions.

Without the ability to simulate what other people are thinking we would be lost in the social world.

The emergence of theory of mind in children is a vital developmental milestone; some psychologists think that a failure to develop a theory of mind is a central component of autism.

Some developmental psychology experiments suggest that at about 4- to 6-years old a range of remarkable skills start to emerge in young children that are vital for their successful functioning in society.

They begin to understand that others can hold false beliefs, they themselves can lie, and that others can lie to them — they have a theory of mind.

7. Object permanence in developmental psychology

Object permanence , or object constancy, in developmental psychology is understanding that things continue to exist, even if you cannot seem them.

Research in developmental psychology has found that infants as young as 3.5 months seem to have a basic grasp of object permanence.

It appears that young infants are not necessarily trapped in a world of shapes which have little meaning for them.

Instead, they seem to be intuitive physicists who can carry out rudimentary reasoning about physical concepts like gravity, inertia and object permanence.

8. How infants learn their first word

An infant’s very first step in their year-long developmental journey to their first word is perhaps their most impressive.

This first step is discriminating and categorising the basic sound components of the language they are hearing.

To get an idea how hard this might be think about listening to someone speaking a language you don’t understand.

Foreign languages can sound like continuous streams of noise in which it’s very hard to pick up where one word starts and another word begins.

Research in developmental psychology finds that until about 11 months of age infants are masters of discriminating phonemes used in all different types of languages.

But after 11 months infants settle down with one set of phonemes for their first language, and lose the ability to discriminate the phonemes from other languages.

9. Play and developmental psychology

The pioneering developmental psychologist Lev Vygotsky thought that, in the preschool years, play is the leading source of development.

Through play children learn and practice many basic social skills.

They develop a sense of self, learn to interact with other children, how to make friends, how to lie and how to role-play.

The classic developmental psychology study of how play develops in children was carried out by Mildred Parten in the late 1920s at the Institute of Child Development in Minnesota ( Parten, 1933 ).

She closely observed children between the ages of 2 and 5 years and categorised the types of play.

She found six different types of play , ranging from solitary, through associative to cooperative

10. Piaget’s developmental psychology theory

Jean Piaget was a developmental psychologist whose four-stage theory, published in 1936, has proved extremely influential.

Piaget’s four stages of development theory  has the dubious claim to fame of being one of the most criticised psychological theories ever.

From the sensorimotor stage, through the pre-operational stage, the concrete operational stage and the formal operational stage, his theory attempts to describe how childhood development progresses.

However, Piaget’s experiments and theories about how children build up their knowledge of the world have faced endless challenges, many of them justified.

Read on about them here .

Author: Jeremy Dean

Psychologist, Jeremy Dean, PhD is the founder and author of PsyBlog. He holds a doctorate in psychology from University College London and two other advanced degrees in psychology. He has been writing about scientific research on PsyBlog since 2004. He is also the author of the book "Making Habits, Breaking Habits" (Da Capo, 2013) and several ebooks. View all posts by Jeremy Dean

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