A new rapid diagnostic test for malaria has sensitivity 80% and specificity 95.6%. In a population with disease prevalence of 10%, the Positive Predictive Value (PPV) of the test is approximately (using the formula):
- A 54%
- B 80%
- C 66% ✓
- D 95%
Correct answer: C. 66%
Explanation
PPV = (Sensitivity × Prevalence) / [(Sensitivity × Prevalence) + (1−Specificity) × (1−Prevalence)] = (0.80 × 0.10) / [(0.80 × 0.10) + (0.044 × 0.90)] = 0.08 / (0.08 + 0.0396) = 0.08/0.1196 ≈ 66.9% ≈ 66%. Despite high sensitivity and specificity, PPV is only ~66% at 10% prevalence because false positives accumulate in the large disease-free population. This demonstrates why screening in low-prevalence populations has poor PPV.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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