A test is evaluated in 300 people. Of 100 with the disease, 90 test positive; of 200 without it, 30 test positive. What is the positive predictive value?
Answer and explanation
Correct answer: D. 75 percent
- Step 1: PPV is true positives divided by all positive results.
- Step 2: There were 90 true positives and 30 false positives, so 120 positives; 90 divided by 120 is 75 percent.
Answer
75 percent.
Why not the others: 30 percent, because 30 healthy people had a false positive result: 30 percent is not a predictive value; 30 is the number of false positives. 90 percent, because 90 of 100 diseased people tested positive: 90 percent is the sensitivity. 85 percent, because 170 of 200 healthy people tested negative: 85 percent is the specificity.
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