A study diagram shows: 'Exposed/Risk factor' → outcome vs. 'Non-exposed/No risk factor' → outcome, with follow-up measuring who develops disease. What type of study does this diagram represent?

Correct answer: D. Cohort study

• A. Incorrect. Cross-sectional studies measure exposure and outcome at the SAME POINT in time — no follow-up.
• B. Incorrect. RCTs involve random assignment of participants to intervention vs. control — the diagram shows exposed vs. non-exposed (observational).
• C. Incorrect. Case-control studies start from the OUTCOME (disease present or absent) and look BACK at exposure — the diagram flows from exposure forward to disease.
• D. Correct. The diagram shows: exposed group → follow-up → disease or no disease; non-exposed group → follow-up → disease or no disease. This is a COHORT STUDY (prospective or retrospective) — participants are grouped by EXPOSURE STATUS at the start and followed forward to measure disease incidence. Also associated with FOREST PLOTS in meta-analyses.