Biostatistics & Study Design USMLE Step 1 Practice Question
A cancer screening program detects numerous tumors with excellent 10-year survival rates. However, interval cancers discovered between screening visits in asymptomatic patients demonstrate aggressive behavior with significantly worse outcomes. Chart review shows screened tumors have mean diameter 1.2 cm versus 3.8 cm for interval cancers. Lead time to diagnosis averages 2 years in screened cohorts. Patients with screened tumors remain asymptomatic at detection. Which bias most likely explains the apparently favorable survival statistics in the screened population?
Answer choices
- ABerkson bias
- BMeasurement bias
- CAttrition bias
- DLength-time biasCorrect answer
- EObserver-expectancy bias
- FLead-time bias
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