definition longitudinal research design
Part of the Customer data management glossary: A longitudinal study is an observational research method in which data is gathered for the same subjects repeatedly over a period of time. Longitudinal research projects can extend over years or even decades. In a longitudinal cohort study, the same individuals are observed over the study period. Cohort studies are common in medicine, psychology and sociology, where they allow researchers to study changes over time.
Definition of longitudinal. 1  1 : placed or running lengthwise The insect's back is black with yellow longitudinal stripes. 2  2 : of or relating to length or the lengthwise dimension the longitudinal extent of the building. 3 : involving the repeated observation or examination of a set of subjects over time with respect to one or more study variables a longitudinal study of juvenile offenders over a period of five years.