A screening programme for diabetic retinopathy is evaluated. Disease prevalence is 5%. Test sensitivity is 90%, specificity is 85%. In a population of 10,000, what is the Positive Predictive Value (PPV)?
- A 24% ✓
- B 41%
- C 64%
- D 90%
Correct answer: A. 24%
Explanation
Diseased = 500; healthy = 9500. TP = 0.90 × 500 = 450; FN = 50; FP = 0.15 × 9500 = 1425; TN = 8075. PPV = TP/(TP+FP) = 450/(450+1425) = 450/1875 = 0.24 = 24%. PPV is critically affected by disease prevalence; even with good sensitivity and specificity, low prevalence produces many false positives and low PPV, an important consideration when choosing community screening programmes.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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