What is the difference between a longitudinal and a cross-sectional study?

Longitudinal studies and cross-sectional studies are two different types of research design. In a cross-sectional study you collect data from a population at a specific point in time; in a longitudinal study you repeatedly collect data from the same sample over an extended period of time.

Longitudinal study Cross-sectional study
Repeated observations Observations at a single point in time
Observes the same group multiple times Observes different groups (a ‘cross-section’) in the population
Follows changes in participants over time Provides snapshot of society at a given point