In a cohort study of hepatitis B infection and hepatocellular carcinoma, 40 of 200 HBsAg-positive persons and 10 of 400 HBsAg-negative persons develop hepatocellular carcinoma over 10 years. The relative risk of hepatocellular carcinoma associated with HBsAg positivity is:
- A 2.0
- B 4.0
- C 8.0 ✓
- D 13.3
Correct answer: C. 8.0
Explanation
Risk in the exposed group is 40 divided by 200, which is 0.20. Risk in the unexposed group is 10 divided by 400, which is 0.025. The relative risk is 0.20 divided by 0.025, equal to 8.0. Option B results from incorrectly using the odds ratio arithmetic, option A halves the correct value through an arithmetic slip, and option D computes the risk ratio of the unexposed to the exposed inverted with wrong denominators. This magnitude matches the classic Beasley cohort in Taiwan.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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