A screening test for cervical cancer has sensitivity 85% and specificity 80%. In a high-prevalence community (disease prevalence 10%), what is the Positive Predictive Value (PPV)?

• A 54%
• B 68%
• C 42%
• D 32% ✓

Explanation

Using a 2×2 table with 1000 people: diseased = 100, non-diseased = 900. TP = 0.85 × 100 = 85; FP = 0.20 × 900 = 180. PPV = TP / (TP + FP) = 85 / (85 + 180) = 85 / 265 ≈ 32.1%. Even with good sensitivity and specificity, PPV is only 32% at 10% prevalence because the absolute number of false positives from the large non-diseased group exceeds true positives. This illustrates why prevalence dramatically affects PPV.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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