A sensitivity of 80% and specificity of 90% is reported for a screening test. In a population where disease prevalence is 10%, what is the Positive Predictive Value (PPV)?
- A 80%
- B 90%
- C 47.1% ✓
- D 66.7%
Correct answer: C. 47.1%
Explanation
PPV = (Sensitivity × Prevalence) / [(Sensitivity × Prevalence) + (1 – Specificity) × (1 – Prevalence)] = (0.8 × 0.1) / [(0.8 × 0.1) + (0.1 × 0.9)] = 0.08 / (0.08 + 0.09) = 0.08/0.17 = 47.1%. PPV is heavily influenced by prevalence; even with good sensitivity and specificity, PPV is low in low-prevalence settings.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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