Review of Positive and Negative Predictive Values
We know that the chance that a positive result is correct (positive predictive value) or the chance a negative result is correct (negative predictive value) will vary depending on the prevalence of the disease in a population.
Multi-choiceAs prevalence of the disease increases, what will happen to the PPV? NPV?
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PPV will increase NPV will increase | |
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PPV will increase NPV will decrease | |
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PPV will decrease NPV will increase | |
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PPV will decrease NPV will decrease |
Multi-choiceAs the prevalence of the disease decreases, what happens to the PPV? what happens to the NPV?
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PPV increases, NPV decreases | |
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PPV increases NPV increases | |
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PPV decreases NPV increases | |
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PPV decreases NPV decreases |
The instability of the PPV and NPV makes it hard to know what to do with a positive or a negative result in a patient if we do not know the prevalence of disease.
This is where the likelihood ratio can help us interpret positive or negative test results.