Methods of Studying Development
10 Developmental Psychology
STEP 4 Review the Knowledge You Need to Score High
Developmental psychologists conduct experiments, naturalistic observations, correlational studies, and case studies that enable them to assess change over time. (See Chapter 6, Research Methods.) They use four basic research designs: longitudinal, cross-sectional, cohort-sequential, and retrospective studies.
A longitudinal study follows the same group of people over a period from months to many years in order to evaluate changes in those individuals. In 1921, Lewis Terman of Stanford University began studying a group of highly intelligent children who have been studied throughout their lives, providing important information about changes in intellectual functioning across the life span. Longitudinal studies can be extremely costly to conduct, take a long time to produce results, and typically lose participants over time. If those who drop out differ from the other subjects in significant ways, results of the study may not be generalizable to the original population.
On the other hand, cross-sectional studies cost less, do not lose participants, and produce results quickly, but they have other major weaknesses. In a cross-sectional study, researchers assess developmental changes with respect to a particular factor by evaluating different age groups of people at the same time. For example, to study life-span changes in mathematical skills, psychologists could give the same math tests to groups of 15-, 25-, 35-, 45-, 55-, 65‑, and 75-year-olds at the same time. Cross-sectional studies can be invalid if a cohort, group of people in one age group, is significantly different in their experiences from other age groups, resulting in the cohort effect, differences in the experiences of each age group as a result of growing up in different historical times. This difference is a confounding variable in the study. Obviously, most younger participants may have been exposed to calculators and computers their whole lives, whereas 65- and 75-year-olds have had fewer opportunities.
To minimize the major drawbacks of both longitudinal and cross-sectional research designs, some researchers conduct cohort-sequential studies. In cohort-sequential studies, cross-sectional groups are assessed at least two times over a span of months or years, rather than just once. Results from one cohort are compared with other cohorts at the same age to evaluate their similarity; differences indicate a cohort effect. In this way, researchers can separate age-related changes from cohort effects. These studies share disadvantages of longitudinal research but to a lesser extent.
Biographical or retrospective studies are case studies that investigate development in one person at a time. Typically, a researcher interviews an individual at the older end of the age span of interest. The researcher reconstructs changes that have occurred in the subject’s life through the subject’s self-reports in interviews and examination of available data. Although these studies can be very detailed, they are not always correct because memory is not always accurate and they may not be generalizable to a larger population.