A screening test for cervical cancer has a sensitivity of 80% and specificity of 90% when applied to a population with a disease prevalence of 1%. What is the Positive Predictive Value (PPV) of the test?
- A 80%
- B 47.0%
- C 7.5% ✓
- D 90%
Correct answer: C. 7.5%
Explanation
Using a population of 10,000: true positives = prevalence × sensitivity = 100 × 0.80 = 80; false positives = (10,000−100) × (1−0.90) = 9900 × 0.10 = 990. PPV = TP / (TP+FP) = 80/(80+990) = 80/1070 ≈ 7.5%. This illustrates the key principle that even with good sensitivity and specificity, PPV is dramatically low when disease prevalence is very low — a fundamental reason screening is reserved for higher-risk populations or uses multiple sequential tests.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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