USMLE Step 1 Quiz
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BIOSTATISTICS AND EPIDEMIOLOGY
Question 1 of 20
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A prospective cohort follows 2,200 adults aged 18–35 without nephrolithiasis to test whether high-dose vitamin C supplementation increases kidney stone incidence over 6 years. Supplement use is recorded annually and verified by purchase receipts when available. Incident kidney stones are confirmed by imaging reports. Results: stones occur in 3.2% of high-dose users vs 1.9% of nonusers. High-dose users also drink less water and consume more animal protein. Investigators adjust for diet but note hydration is hard to measure accurately.
Which bias is most likely to affect the results of this study?
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