A screening test is applied to a population where disease prevalence is 1%. The test has 99% sensitivity and 99% specificity. What is the Positive Predictive Value (PPV)?
- A 50% ✓
- B 99%
- C 90%
- D 1%
Correct answer: A. 50%
Explanation
Using 10,000 population: True Positives = 0.01 × 10000 × 0.99 = 99; False Positives = 9900 × 0.01 = 99. PPV = 99/(99+99) = 99/198 = 50%. This demonstrates how low prevalence drastically reduces PPV even with high sensitivity and specificity. Options B and C are far too high; D is not calculated correctly.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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