A screening test for cervical cancer has sensitivity 80% and specificity 90%. When applied to a population with a disease prevalence of 2%, the Positive Predictive Value (PPV) is CLOSEST to:

• A 80%
• B 45%
• C 6%
• D 14% ✓

Explanation

Using a population of 10,000: prevalence 2% = 200 diseased, 9800 healthy. True positives (TP) = 200 × 0.80 = 160; False positives (FP) = 9800 × 0.10 = 980. PPV = TP / (TP + FP) = 160 / (160 + 980) = 160/1140 ≈ 14%. This illustrates the critical impact of prevalence on PPV: even a moderately accurate test has low PPV when applied to a low-prevalence population, generating many false positives. This principle governs the design and appropriateness of population screening programmes. NPV = 9800 × 0.90 / (9800 × 0.90 + 200 × 0.20) = 8820 / 8860 ≈ 99.5%.

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

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Written and medically reviewed by the StethoPrep medical team.