Longitudinal Study

Studies where the same group of participants is tested repeatedly over time. This design is often used in developmental research to examine the way personality and behavior change across the life span. The advantage of longitudinal designs over their alternative, cross-sectional designs (see definition), is that longitudinal designs do not suffer from cohort effects, in which people of particular age groups, or cohorts, share particular sets of life circumstances (e.g., being teenagers in the late 1950s versus being teenagers in the new millennium) so that development stage at comparison (e.g., comparing older adults with adolescents in 2008) is confounded with other life circumstances. The disadvantage of longitudinal research is in the high rate of attrition that occurs over time. Also, in the same way that cross-sectional designs are vulnerable to cohort effects, longitudinal designs are vulnerable to secular trends (general trends that occur in society and that may affect the results of the longitudinal study by confounding age with time of testing). For example, finding that participants improve at programming software as they age may be the result of developmental changes, or it may be the result of general growth in societal proficiency with technology.