What is meant by a "longitudinal study"?

A longitudinal study is defined as a research design that involves repeated observations of the same variables over an extended period. This approach allows researchers to track changes and developments over time within the same subjects, which can provide valuable insights into trends, effects, and long-term outcomes. For instance, in psychological or sociological research, a longitudinal study might follow the same group of individuals to observe how their behavior, attitudes, or health change across several years. This method contrasts with cross-sectional studies, which analyze data from different demographics at one point in time.

The strength of longitudinal studies lies in their ability to establish sequences of events or causal relationships, as they reveal how variations in one variable over time can correlate with changes in another variable. This sets them apart from other research methods that may capture a snapshot rather than a dynamic process.