Epidemiology & Prevention USMLE Step 1 Practice Question
In a clinical trial evaluating a new antihypertensive medication, researchers randomly assign 1,000 patients to either drug or placebo. At baseline, the drug group has a mean systolic BP of 158 mmHg and the placebo group has a mean of 156 mmHg. This difference is statistically significant (p = 0.03) but both groups were randomly assigned. Which of the following best explains this finding?
Answer choices
- AConfounding by socioeconomic status
- BSelection bias in patient enrollment
- CThe drug causes an increase in baseline blood pressure
- DThe randomization process failed
- EBaseline imbalance due to random chance despite successful randomizationCorrect answer
- FMeasurement error in systolic blood pressure recording at baseline
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