In a study of 500 patients, the sensitivity and specificity of a new test are each 90%. The prevalence of the disease is 10%. The positive predictive value (PPV) is closest to:
- A 67%
- B 50% ✓
- C 50%
- D 33%
Correct answer: B. 50%
Explanation
With prevalence 10% in 500 patients: true positives = 500×0.10×0.90 = 45; false positives = 500×0.90×0.10 = 45. PPV = 45/(45+45) = 45/90 = 50%. This illustrates how even with high sensitivity and specificity, PPV is relatively low when prevalence is low.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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