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A cohort refers to a group of people that were born at the same period of time. They are likely to share some common experiences such as social, cultural, and historical influences that are unique to them. Examples of well-known cohorts include "baby boomers" and "Generation Xers." Cohort effects arise when changes in performance are due circumstances specific to a particular time and place, rather than age. Thus, if looking at physical development, children born during times of conflict or war may have retarded physical growth due to stress and food deprivation. Therefore, growth pattern norms might be inaccurate if based on this cohort. Another example would be gender differences in vocational aspirations for adolescents. Career choices by males and females could depend on whether fifteen-year-olds born in 1985 participated in the study versus fifteen-year-olds born in 1935. Both cross-sectional and longitudinal research designs are susceptible to cohort effects. A cross-sequential design may be used when cohort effects are suspected.


Miller, Scott. Developmental Research Methods, 2nd edition. Englewood Cliffs, NJ: Prentice-Hall, 1998.

Katherine M. Robinson

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Social Issues ReferenceChild Development Reference - Vol 2