Biostatistics & Study Design USMLE Step 1 Practice Question
A researcher designs two prospective studies to investigate whether dietary sodium restriction reduces the incidence of atrial fibrillation in older adults. Study A enrolls 200 nursing home residents without atrial fibrillation and randomly assigns them to either a low-sodium diet (target <2g/day) or usual diet. Study B enrolls 200 independent-living seniors without atrial fibrillation and stratifies them by self-reported dietary sodium intake using 24-hour dietary recall questionnaires. Both cohorts are followed for 12 months with clinical assessments for new-onset atrial fibrillation at baseline, 6 months, and 12 months. Which of the following statements most accurately compares the methodological strengths and limitations of these two study designs?
Answer choices
- AStudy B has greater statistical power because it uses continuous measurement of sodium intake rather than categorical assignment
- BStudy A is more susceptible to selection bias because randomization was performed within an institutional setting
- CStudy A provides superior control of confounding variables through the randomization processCorrect answer
- DStudy B allows stronger causal inference because the observational design reflects real-world dietary patterns
- EStudy A cannot use inferential statistical testing because atrial fibrillation is a dichotomous outcome
- FStudy B minimizes recall bias by requiring participants to estimate sodium intake over a 24-hour period
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