A diagnostic study reports Sensitivity = 75%, Specificity = 85%, prevalence = 20%. What is the Negative Predictive Value (NPV)?

• A 85%
• B 75%
• C 55.6%
• D 93.9% ✓

Explanation

Using Bayes' theorem: NPV = [Specificity × (1 – Prevalence)] / [(Specificity × (1 – Prevalence)) + (1 – Sensitivity) × Prevalence] = [0.85 × 0.80] / [0.85 × 0.80 + 0.25 × 0.20] = 0.68 / (0.68 + 0.05) = 0.68/0.725 = 93.8% ≈ 93.9%. NPV is high when prevalence is low and specificity is high.

Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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