A test with sensitivity 90 percent and specificity 90 percent is used in 1,000 people with a disease prevalence of 10 percent. What is the positive predictive value?
Answer and explanation
Correct answer: A. 50 percent
- Step 1: There are 100 with disease, of whom 90 test positive; of the 900 without disease, 10 percent (90) test positive. Step 2. Positive predictive value is 90 divided by 180, which is 50 percent. Answer: 50 percent. Why not the others: Predictive value depends on prevalence. It is not equal to the prevalence. Multiplying the two figures has no meaning.
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