Which study design best establishes a temporal relationship between exposure and disease outcome?

A prospective cohort study follows disease-free participants over time, measuring exposures at baseline and observing who develops the disease. Because exposure is measured BEFORE disease onset, a clear temporal relationship (cause precedes effect) can be established. This is crucial for inferring causation. While an RCT also establishes temporal relationships, cohort studies are observational and can study exposures that cannot ethically be randomized. Case-control studies look backward (retrospective), and cross-sectional studies measure exposure and outcome simultaneously, making temporal inference difficult.