[R] Cohort study(Same sample) and Longitudinal study(New sampling)

Cohort studies are usually prospective longitudinal studies - i.e. they follow they same sample through multiple waves forward in time. Longitudinal studies can also be repeated cross-sectional studies, which involve collecting data from a new or largely new sample at multiple points in time. Longitudinal studies can also gather data on past events, which is a retrospective design.