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Definition of Study, longitudinal
Medically reviewed by Min Clinic Staff | Updated: January 2026
Study, longitudinal: A study done over the passage of time. For example, a longitudinal study of children with Down syndrome (trisomy 21) might involve the study of 100 children with this condition from birth to 10 years of age. Also called a diachronic study. The opposite of a cross-sectional (synchronic) study.