A screening test for gestational diabetes has a sensitivity of 80% and specificity of 90%. It is applied to a pregnant population with 10% prevalence of the condition. The negative predictive value is approximately:
- A 98% ✓
- B 92%
- C 88%
- D 72%
Correct answer: A. 98%
Explanation
In 1000 women, 100 have gestational diabetes. With 80% sensitivity, 80 are detected and 20 missed (false negatives). Of the 900 non-diseased women, 90% specificity gives 810 true negatives. NPV equals true negatives divided by all test negatives, 810 divided by 830, about 98%. Option B (92%) tempts those who confuse this with a value derived from prevalence alone rather than from the two-by-two table.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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