Understanding Psychology (10th Ed)

 cross-sectional research,  compares people of different ages at the same point in time. 
Cross-sectional studies provide information about differences in development 
between different age groups (Creasey, 2005; Huijie, 2006).
Suppose, for instance, we were interested in the development of intellectual abil-
ity in adulthood. To carry out a cross-sectional study, we might compare a sample 
of 25-, 45-, and 65-year-olds who all take the same IQ test. We then can determine 
whether average IQ test scores differ in each age group. 
Cross-sectional research has limitations, however. For instance, we cannot be 
sure that the differences in IQ scores we might fi nd in our example are due to age 
differences alone. Instead, the scores may refl ect differences in the educational 
attainment of the cohorts represented. A cohort is a group of people who grow up 
at similar times, in similar places, and in similar conditions. In the case of IQ 
identical twins
Twins who are 
genetically identical.
cross-sectional research
A research 
method that compares people of 
different ages at the same point in time.
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384 Chapter 
12 
Development
R E C A P / E V A L U A T E / R E T H I N K
R E C A P 
How do psychologists study the degree to which development 
is an interaction of hereditary and environmental factors?
• Developmental psychology studies growth and change 
throughout life. One fundamental question is how much 
developmental change is due to heredity and how much 
is due to environment—the nature–nurture issue. 
Heredity seems to defi ne the upper limits of our growth 
and change, whereas the environment affects the degree 
to which the upper limits are reached. (p. 381)
• Cross-sectional research compares people of different 
ages with one another at the same point in time. In con-
trast, longitudinal research traces the behavior of one or 
more participants as the participants become older. 
Finally, sequential research combines the two methods 
by examining several different age groups at several 
points in time. (p. 383)