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Letters
December 1, 2010

Using Restriction to Minimize Bias in Observational Studies

JAMA. 2010;304(21):2359-2360. doi:10.1001/jama.2010.1727

To the Editor: In their Commentary, Drs Psaty and Siscovick1 emphasized the importance of restriction to minimize confounding by indication and bias in the conduct of observational comparative effectiveness research. We agree with this strategy for less complicated therapies, such as β-blockers for hypertension, for which the dose-adjusted efficacy would not likely be affected by clinician-level, facility-level, or other nonpatient factors. However, we caution against the broad use of restriction to evaluate therapies or services for which quality of care delivery would impact effectiveness.

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