The matching negative predictive value

Intermediate

Topic: Predictive values of a test · more questions on this topic

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Using the test and the prevalence from the previous exercise, compute the negative predictive value. Say, in one sentence, which of the two predictive values a negative result and a positive result should be quoted with.

Worked answer

\mathrm{NPV}=\frac{0.98\times 0.90}{0.98\times 0.90+0.02\times 0.02}=\frac{0.882}{0.8824}\approx 0.9995.

A positive result should be quoted with the PPV, about 0.17. A negative result should be quoted with the NPV, about 0.9995. The same test is weak evidence that the condition is present and strong evidence that it is absent.