What best describes a longitudinal study?

A longitudinal study is characterized primarily by its method of observing the same participants over a prolonged period, which allows researchers to track changes and developments within those individuals. This type of study is especially useful for examining trends over time, discerning patterns in behavior, health, or other variables, and establishing cause-and-effect relationships.

By following the same participants, researchers can gather valuable data on how experiences or treatments affect individuals over time, making it possible to identify outcomes that may not be visible in a one-time snapshot of a population. This approach contrasts with analyses that capture data at only a single point in time, where influences of time and change cannot be factored in.