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Length-time bias — USMLE Step 3 MCQ

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HardPreventive Medicine, Epidemiology, BiostatisticsLength-time biasUSMLE Step 3

A cancer screening test disproportionately detects slow-growing tumors. Screen-detected cases appear to have better prognosis than symptom-detected cases even when treatment is similar. Mortality reduction is uncertain. Which of the following is the most likely explanation for this patient's findings?

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Correct answer: C — Indolent disease is more likely to be found by periodic screening

Length-time bias occurs when screening preferentially identifies slower-growing disease.

Reference: USPSTF A and B recommendations, https://www.uspreventiveservicestaskforce.org/uspstf/recommendation-topics/uspstf-a-and-b-recommendations