A study compares 100 obese and 100 non-obese adults for hypertension. Among the obese, 30 have hypertension; among the non-obese, 15 do. Which statement about the calculated measures of association is correct?

• A The relative risk is 2.0 and the odds ratio is 2.43 ✓
• B Both the relative risk and odds ratio equal 2.0
• C The relative risk is 2.43 and the odds ratio is 2.0
• D The relative risk is 2.43 and the odds ratio is 2.43

Explanation

Relative risk = (30/100) / (15/100) = 2.0. Odds ratio = (30 x 85) / (70 x 15) = 2550/1050 = 2.43. Because hypertension is common in this population (22.5 percent overall), the rare-disease assumption fails and the odds ratio overestimates the relative risk. The two converge only when the outcome frequency is low, typically below 10 percent, so option B holds only under that condition.

Reference: Gordis Epidemiology, 6th ed.

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