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Predictive value prevalence — USMLE Step 3 MCQ

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HardPreventive Medicine, Epidemiology, BiostatisticsPredictive value prevalenceUSMLE Step 3

A clinic introduces screening for a rare disease in a low-prevalence population. The test has high sensitivity and specificity, but many positive results are false positives compared with a specialty clinic population. The test has not changed. Which of the following is the most likely explanation for this patient's findings?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: B — Lower disease prevalence reduces positive predictive value

Positive predictive value falls as disease prevalence decreases, even when sensitivity and specificity are unchanged.

Reference: Current US clinical practice standards and USMLE Step 3 content outline, https://www.usmle.org/exam-resources/step-3-materials