What distinguishes a longitudinal study from a cross-sectional study?

A longitudinal study is distinctive because it involves tracking and observing the same subjects over an extended period. This allows researchers to detect changes and developments over time within the same individuals, making it particularly valuable for understanding trends, life changes, or progressions in behaviors or conditions.

In contrast, a cross-sectional study captures data at a single point in time, which means it compares different subjects or groups to explore various phenomena. While this method is efficient for obtaining a snapshot view of a population, it does not provide insights into how individual subjects evolve over time.

The other options underscore aspects that do not define the core distinction between these types of studies. For instance, while longitudinal studies may require a larger initial commitment of time and resources due to the repeated measures over time, they are not necessarily faster than cross-sectional studies, which can quickly gather data from a wide array of subjects. Additionally, the nature of sampling size is not a defining characteristic; both study types can be designed with various sample sizes according to research requirements. Hence, the key differentiator remains the emphasis on tracking the same subjects in longitudinal studies.