Which study design MOST clearly provides a temporal relationship between exposure and disease (cause before effect)?

Correct answer: A. Cohort study (prospective — follows exposed and unexposed groups forward in time)

• A. Correct. Cohort studies establish temporality most clearly among observational studies because participants are classified by EXPOSURE STATUS first, then followed forward in time to observe who develops the disease. This design directly shows that exposure preceded the outcome.
• B. RCTs provide the strongest evidence for causation, but the question asks specifically about temporal relationship, which cohort studies (prospective observational) most clearly demonstrate among study designs.
• C. Cross-sectional studies measure exposure and disease simultaneously (snapshot in time) — no temporal relationship can be established.
• D. Case-control studies START with disease status and look BACKWARD — they cannot directly establish temporal sequence as clearly as cohort studies.