In a screening program, a test with sensitivity 90% and specificity 80% is applied to a population with a disease prevalence of 2%. The positive predictive value (PPV) is approximately:
- A 18.0%
- B 44.0%
- C 8.4% ✓
- D 90.0%
Correct answer: C. 8.4%
Explanation
Using a hypothetical 10,000 population: disease present = 200 (2%), disease absent = 9,800. True positives = 0.90 × 200 = 180. False positives = 0.20 × 9,800 = 1,960. PPV = 180 / (180 + 1960) = 180 / 2140 ≈ 8.4%. At low prevalence, even a specific test has a low PPV, producing many false positives — this is a fundamental principle of screening.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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