What are the types of longitudinal studies?
Longitudinal studies are broadly categorized as prospective (researchers recruit participants and collect their data over the following years) or retrospective (researchers use an existing longitudinal dataset to “look back in time” at factors contributing to an outcome of interest).
Specific longitudinal study designs include the following.
- Repeated cross-sectional study: Researchers collect the same data from distinct samples of the same population over time (essentially a cross-sectional study that is repeated with different people).
- Cohort study: Participants who share one or more characteristics (or “exposures”) are followed over time to observe which outcomes they develop.
- Panel study: A group of participants, often randomly selected, is studied over time to observe changes in their attitudes or behaviors.