A new rapid test for cervical cancer precursors is evaluated. In 1000 women, 50 truly have CIN-III. The test identifies 40 of these 50 (sensitivity 80%). Of the 950 who do not have CIN-III, the test incorrectly flags 95 (specificity 90%). What is the Positive Predictive Value (PPV) of this test in this population?

• A 80%
• B 90%
• C 99.5%
• D 29.6% ✓

Explanation

True positives = 40. False positives = 95. PPV = TP/(TP+FP) = 40/(40+95) = 40/135 = 29.6%. This relatively low PPV despite reasonable sensitivity and specificity reflects the low prevalence (5%) of CIN-III in this group, demonstrating Bayes' theorem: PPV is highly dependent on disease prevalence. Higher specificity would reduce false positives and raise PPV. This principle is critical for designing population screening programmes.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.