A screening test for diabetes has sensitivity 80% and specificity 90%. In a population with 10% diabetes prevalence, the Positive Predictive Value (PPV) is approximately:
- A 57%
- B 67%
- C 47% ✓
- D 80%
Correct answer: C. 47%
Explanation
In 1000 people: 100 have diabetes (10%). True Positives = 80% × 100 = 80; False Positives = 10% × 900 = 90. PPV = TP/(TP+FP) = 80/170 ≈ 47%. This illustrates that PPV falls dramatically at low prevalence despite good sensitivity and specificity, because the absolute number of false positives swamps true positives. PPV is critically dependent on prevalence, unlike sensitivity and specificity which are fixed test characteristics.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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