What type of study follows a group over time, making it prospective?

A cohort study is characterized by its prospective nature, as it involves selecting a group of individuals who share a common characteristic or experience and following them over a period of time to observe outcomes. This design allows researchers to assess how exposure to certain risk factors affects the likelihood of developing specific outcomes or diseases in the future.

In a cohort study, researchers gather data at the beginning of the study regarding participants' exposures and health status. They then follow these participants over time, collecting additional data on health outcomes. This longitudinal approach facilitates the establishment of temporal relationships between exposure and outcome, which can strengthen the evidence for causal links.

In contrast, other study designs, such as case-control studies and cross-sectional studies, do not follow subjects over time. A case-control study looks backward to compare subjects with a specific outcome to those without the outcome, and a cross-sectional study measures exposures and outcomes simultaneously at a single point in time. Although randomized controlled trials can be prospective, they are not necessarily cohort studies, as they involve an intervention and control group dynamics rather than merely observing a cohort's natural progression. Thus, cohort studies are distinctly aligned with the prospective approach.