In a case-control study, 200 cases and 200 controls are enrolled. Exposure prevalence among cases is 60% and among controls is 40%. The odds ratio is:

• A 1.5
• B 2.0
• C 3.0
• D 2.25 ✓

Explanation

OR = (exposed cases × unexposed controls) / (unexposed cases × exposed controls) = (120 × 120) / (80 × 80) = 14400 / 6400 = 2.25. With 200 cases: exposed cases = 120, unexposed = 80; with 200 controls: exposed = 80, unexposed = 120. The OR of 2.25 indicates approximately 2.25-fold higher odds of exposure among cases versus controls.

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

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