Longitudinal Research

Longitudinal research is generally defined as studies that investigate change over time with the same cohort(s). This definition characterizes four key features of longitudinal research.

First, by change, it means that longitudinal studies focus on a dynamic process rather than a static status as the outcome variable. A process is a series of changes from the initial status to the final status through various intermediate statuses. In a methodological term, one status is often called one wave. Thus, longitudinal studies use multiple waves to represent a process.

Second, by over time, it means that longitudinal studies must include the time dimension as the fundamental predictor. A multiwave process can be considered as a function of time, and various substantive predictors (e.g., gender or IQ scores) can be ...