A community screening programme for cervical cancer using VIA (Visual Inspection with Acetic acid) is being evaluated. In a population of 10,000 women, 500 have pre-cancerous lesions (CIN 2+). VIA detects 400 of these (TP) and misses 100 (FN). Of the 9,500 without disease, 1,900 test positive (FP) and 7,600 test negative (TN). The Positive Predictive Value (PPV) of VIA in this population is:
- A 80%
- B 17.4% ✓
- C 98.7%
- D 40%
Correct answer: B. 17.4%
Explanation
PPV = TP / (TP + FP) = 400 / (400 + 1900) = 400 / 2300 = 17.4%. This low PPV reflects the low prevalence of CIN 2+ (500/10,000 = 5%) and the high false positive rate of VIA. Sensitivity = TP/(TP+FN) = 400/500 = 80% (option A is sensitivity, not PPV). Specificity = TN/(TN+FP) = 7600/9500 = 80%. NPV = TN/(TN+FN) = 7600/7700 = 98.7% (option C). PPV is strongly influenced by disease prevalence — in lower prevalence settings, PPV drops further. This explains why VIA-positive women require colposcopic confirmation before treatment.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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