Longitudinal Data

Longitudinal data is data that measures the same value or variable over a period of time. We collect longitudinal data when we plop our lawn chair down at the beach and count the number of sandcastles destroyed by beach bullies each hour. We’re focused on one thing (sandcastles returned to the Mother Sand) and track its value over time. Not to be confused with cross-sectional data which measures a number of different variables at the same instant.