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Predictive value and disease prevalence — USMLE Step 3 MCQ

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ModeratePreventive Medicine, Epidemiology, BiostatisticsPredictive value and disease prevalenceUSMLE Step 3

A cohort study finds that a screening test has a sensitivity of 90% and specificity of 80%. The test is then used in a population with a much lower disease prevalence than the original study population. Which of the following test characteristics is most likely to decrease?

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Correct answer: A — Positive predictive value

Positive predictive value decreases as disease prevalence falls, even if sensitivity and specificity remain constant. Negative predictive value increases when prevalence is lower.

Reference: Standard epidemiology principles; USMLE Step 3 content outline