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Definition of Longitudinal study
Medically reviewed by Min Clinic Staff | Updated: January 2026
Longitudinal study: A study done over the passage of time. For example, a longitudinal study of children with Down syndrome might involve the study of 100 children with this condition from birth to 10 years of age. Longitudinal study is the opposite of cross-sectional (synchronic) study. Also known as diachronic study.