What characterizes a longitudinal study in research?

A longitudinal study is characterized by tracking the same subjects over an extended period. This design allows researchers to observe changes and developments in the same individuals across time, making it possible to identify trends, causation, and the long-term effects of variables. By following the same group of participants, researchers can gather more consistent and in-depth data regarding their behaviors, experiences, or outcomes over time.

Tracking the same subjects is particularly valuable in fields such as psychology, medicine, and social science, where understanding how individuals change or how certain conditions evolve can provide significant insights. For instance, in a study examining the impact of a therapy on mental health, observing the same individuals allows the researcher to pinpoint long-term effects and track progress or regression reliably.

The other options describe different research methodologies. Sampling different subjects over time focuses on cross-sectional studies, gathering data at a single point pertains to snapshot studies, and employing randomized selection relates to designs aimed at minimizing bias. These approaches lack the time component that defines longitudinal research, which is crucial for examining developmental and relational changes.