Biostatistics & Study Design USMLE Step 1 Practice Question
A propensity-matched observational study compares beta-blocker therapy versus no beta-blocker after myocardial infarction in 500 post-MI patients. After matching, investigators report a standardized mean difference of 0.03 for age between groups. Baseline characteristics show similar troponin I levels and ejection fraction (35-40%) between cohorts. No significant differences exist in prior medication use. Which interpretation of this standardized mean difference is most appropriate?
Answer choices
- AMatching failed because the value is below zero
- BAge is well balanced between groupsCorrect answer
- CThe study has low external validity
- DAge remains strongly imbalanced between groups
- EThe age difference is statistically significant
- FThe observed age difference represents clinically meaningful variation requiring further adjustment
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