Positive predictive value and prevalence
A screening test with fixed sensitivity and specificity is moved from a high-risk clinic to the general population, where the disease is much rarer. What happens?
Answer A: explanation for every choice
A
Correct. With lower prevalence, false positives make up a larger share of all positive results, so PPV falls.
B
PPV rises with prevalence, not as prevalence falls.
C
Sensitivity is a property of the test and doesn't depend on prevalence.
D
Specificity is also a property of the test.
TakeawayLower prevalence → lower PPV, higher NPV. Sensitivity and specificity stay the same.
Equation usedSensitivity, specificity, and predictive values
Next question →Reviewed 2026-11-05 by a medical student. Spot an error? Report it with question ID ps170.