Incidence vs. prevalence
A new treatment greatly extends survival for a chronic disease but does not cure it. If the number of new cases each year stays the same, how do prevalence and incidence change?
Answer D: explanation for every choice
A
Incidence measures new cases, which the stem says stay the same.
B
Neither falls. Longer survival adds existing cases.
C
Prevalence would fall only if cases resolved faster or patients died sooner.
D
Correct. Prevalence counts all existing cases, and people now live longer with the disease. Incidence counts only new cases, which are unchanged.
TakeawayPrevalence ≈ incidence × duration.
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Reviewed 2026-11-05 by a medical student. Spot an error? Report it with question ID ps93.