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Scientific Method and Human Development

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At the end of the session, the student is expected to:
1. Define development, focusing on three elements of its scientific study and noting how dynamic-systems theory highlights the interactive nature of development. 2. Describe the ecological-systems approach to the study of human development, and explain how this approach leads to an understanding of the overlapping contexts in which people develop. 3. Identify five characteristics of development.

4. List and describe the basic steps of the scientific method. 5. Describe three basic research designs used by developmental psychologists.

Study Guide

The science of human development seeks to understand how and why people—all people, everywhere—change with increasing age, and how and why they remain the same. The science of human development is empirical, meaning that it focuses on data, facts, observation, and experimentation.

The emphasis on the interaction between people and within each person is highlighted by dynamic-systems theory, which stresses fluctuations and transitions. The approach that emphasizes the influence of the systems, or contexts, that support the developing person is Urie Bronfenbrenner’s ecological-systems approach. According to this model, human development is supported by systems at four nested levels: the microsystem (immediate social setting), the exosystem (the local institutions such as school and church), the macrosystem (cultural values, political processes, economic policies, and social conditions), and the chronosystem, which emphasizes the importance of historical time on development. A fifth system, the mesosystem, involves systems, or parts of a single system.

Development is multidirectional, multicontextual, multicultural, multidisciplinary, and plastic.

Two important insights of the multidirectional aspect of this perspective are the concepts of dynamic change, which refers to the continual change that occurs within each person and each social group, and the butterfly effect, in which even a tiny change in one system can have a profound effect on the other systems of development.

Researchers take a broader view of development, recognizing the influence on development of external forces, that is, the context of development. This larger perspective makes it imperative that development be understood in its social context, including its historical and socioeconomic contexts. A cohort is a group of people born within a few years of each other who tend to share certain historical and social influences and perspectives.

Socioeconomic status (SES) is determined by several overlapping variables, including income, education, place of residence, and occupation. Although low income obviously limits a person, other factors (such as education) can make poverty better or worse.

Culture affects development in a multitude of interrelated ways, from whether to cover your mouth when laughing to what to eat for breakfast. Cultures are dynamic, always changing, as people change and grow older. People can belong to more than one culture, with their choice dependent on their immediate context.

An ethnic group is a collection of people who share certain attributes, such as ancestry, national origin, religion, and/or language. Although race was once defined as a biological category, it is actually a social construction.

The three domains of development include the biosocial domain (brain and body as well as changes in them and the social influences that guide them), the cognitive domain (thought processes, perceptual abilities, and language mastery, as well as the educational institutions that encourage them), and the psychosocial domain (emotions, personality, and interpersonal relationships with family, friends, and the wider community).

All three domains are important at every age, and each of the domains is affected by the other two. The value of an interdisciplinary approach to understanding human development can be seen in research on mirror neurons, which are brain cells that respond to the observed actions of others. These neurons, which in the human brain reflect gestures, mouth movements, and whole-body actions, may help explain some aspects of social organization and how culture is transmitted.

One of the most encouraging aspects of the science of development is that development is characterized by plasticity, or the capability of change. One remarkable example is resilience, which is the ability of some children to overcome severe threats to their development. Collective efficacy refers to the degree to which neighbors create a functioning, informal network of people who show concern for each other.

The scientific method consists of five basic steps: (1) formulate a research question, (2) develop a hypothesis, (3) test the hypothesis, (4) draw conclusions, and (5) make the findings available. Replication of research findings verifies the findings and leads researchers to more definitive and extensive conclusions. In replicating research, scientists use a different but related set of participants.

In designing research, scientists are concerned with four issues: validity, reliability, generalizability, and usefulness. There are many ways to test hypotheses. One method is scientific observation of people in their natural environment or in a laboratory setting. Observation is limited in that it tells us only if two variables are correlated. Experiments can reveal cause-and-effect relationships by allowing experimenters to observe whether a change in an independent variable affects some specific behavior, or dependent variable. In an experiment, the participants who receive a particular treatment constitute the experimental group; the participants who do not receive the treatment constitute the comparison group (control group). Statistics are often used to analyze experimental results. Sometimes results are reported by effect size. To determine whether a difference between two groups occurred purely by coincidence, or chance, researchers apply a test of significance.

The survey is especially vulnerable to bias: The group being surveyed may not be representative of the group of interest, the phrasing and order of the questions may affect the responses obtained, and people may give answers to make themselves look better. The interpretation of case study data depends on the researcher’s insightfulness. In cross-sectional research, groups of people who are different in age but similar in all other important ways are compared on the characteristic that is of interest to the researcher(s). One limitation of cross-sectional research is that it is always possible that some variable other than age differentiates the groups. In longitudinal research, the same people are studied over a period of time.Longitudinal research is particularly useful in studying developmental trends that occur over a long age span. Both longitudinal and cross-sectional researchers must bear in mind that research on a cohort may not be valid for people developing in an earlier or later cohort. In cross-sequential research, several groups of people at different ages (crosssectional component) are followed over time (longitudinal component).

Correlation is a number indicating the degree of relationship between two variables. A correlation is positive if both variables tend to increase together or decrease together, negative if one variable tends to increase when the other decreases, and zero if no connection is evident. Correlation does not prove causality. Because numbers can be easily summarized and compared, scientists often rely on data produced by quantitative research. This method may be particularly limiting when researchers describe child development. Also, many developmental researchers use qualitative research that asks open-ended questions.


A. Developmental Fact or Myth? True or False.
1. The science of human development is the study of how and why people change as they grow older, as well as how and why they remain the same. 2. A small change in behavior can have a large impact on the person. 3. Culture, ethnicity, race, and SES are impossible for scientists to disentangle. 4. People can belong to only one culture.

5. Understanding development at any age requires a consideration of the interplay of the biosocial, cognitive, and psychosocial domains of development. 6. Most developmental psychologists prefer not to use the scientific method in studying human development. 7. For the most accurate results, scientific observation should be performed in a laboratory. 8. An experiment is always the best way to investigate a developmental issue. 9. Developmental psychologists almost never base their research on the study of one group of people over a long period of time. 10. When two variables are correlated, it means that one caused the other.

B. Your Cohort: Describe the cohort into which you were born by answering the following questions. 1. In what year were you born?
2. Do you know of any important historical events that occurred at the time of your birth? If so, list a few of them. 3. What important events do you remember as having affected you and your classmates during your school years (for example, assassinations, space exploration, political upheavals or wars, natural disasters)? Describe, if you can, how these events influenced your development. 4. When you were in grade 6, what attitude did most of the people you knew have toward the following?

a. mothers who worked outside the home
b. fathers’ roles in child rearing
c. people of other ethnic groups
d. senior citizens
e. couples without children
f. only children
g. handicapped children
h. birth control

C. Critical Thinking Activity: Breast-Feeding and Intelligence Now that you have read and reviewed Chapter 1, take your learning a step further by testing your critical thinking skills on this scientific reasoning exercise. Several studies suggest that breast-fed babies become more intelligent children than formula-fed babies. One such study (Mortensen, Michaelsen, Sanders, & Reinisch, 2002) involved a sample of over 3,000 women and men born in Copenhagen, Denmark, between October 1959 and December 1961. The samples were divided into five categories based on duration of breast-feeding, as assessed by physician interview with mothers at a one-year examination. The child’s intelligence was assessed using the Wechsler Adult Intelligence Scale (WAIS) at a mean age of 27.2 years. The results showed that duration of breast-feeding was associated with significantly higher scores on the verbal, performance, and full scale WAIS IAs. This difference was observed even after the researchers adjusted for differences in the social class and maternal education of the two groups. (This adjustment allowed the researchers to rule out any preexisting differences in the groups that might have independently contributed to IQ differences in their children.)

The authors acknowledged that other differences between the groups, such as the children’s genetic potential or their parents’ caregiving skills or motivation to nurture, could explain the results. However, they believe that human milk contains various hormones and other factors that enhance brain growth and maturation. 1. State the research hypothesis in your own words. Identify the independent and dependent variables, and define all important concepts and terms as they are used in this study. 2. What evidence do the researchers offer as a test of their hypothesis? Is this evidence empirical (observable)? Is it valid? 3. What explanation do the researchers offer for their findings? Does this explanation make sense based on the evidence? 4. Given the results of this study, why can’t the researchers draw a causal connection between type of food and later intelligence? What might be an alternative explanation for the results of this study? What could the researchers do in order to make a causal connection between the dependent and independent variables? 5. Are there any practical implications for this research?

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