A retrospective cohort study differs from a prospective cohort study primarily in that:

• A Retrospective cohort studies cannot calculate relative risk
• B Retrospective cohort studies are always hospital-based
• C Retrospective cohort studies are identical to case-control studies
• D In retrospective cohort, both exposure and outcome data have already occurred and are assembled from records ✓

Explanation

In a retrospective (historical) cohort study, both exposure and outcome have already occurred; the researcher identifies the cohort from past records and traces outcomes to the present. This is still a cohort design (exposure precedes outcome), and relative risk can be calculated. In a prospective cohort, exposure is identified now and the cohort is followed forward in time. Retrospective cohorts are faster and cheaper but rely on record quality.

Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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