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Propensity Score Adjustment With Multilevel Data: Setting Your Sites on Decreasing Selection Bias

Michael E. Griswold, PhD; A. Russell Localio, PhD; and Cynthia Mulrow, MD, MSc, Senior Deputy Editor
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From Center of Biostatistics, University of Mississippi Medical Center, Jackson, MS 39216; Center for Clinical Epidemiology and Biostatistics, University of Pennsylvania, Philadelphia, PA 19104; and American College of Physicians, Philadelphia, PA 19106.

Acknowledgment: The authors thank Ray and colleagues for providing their analytic data set and assistance in obtaining permission from the State of Tennessee Bureau of TennCare and Department of Health for its use.

Potential Conflicts of Interest: Disclosures can be viewed at www.acponline.org/authors/icmje/ConflictOfInterestForms.do?msNum=M10-0315.

Requests for Single Reprints: Michael E. Griswold, PhD, Center of Biostatistics, University of Mississippi Medical Center, 2500 North State Street, Jackson, MS 39216; e-mail, mgriswold@dor.umsmed.edu.

Current Author Addresses: Dr. Griswold: Center of Biostatistics, University of Mississippi Medical Center, 2500 North State Street, Jackson, MS 39216.

Dr. Localio: Center for Clinical Epidemiology and Biostatistics, University of Pennsylvania, 606 Blockley Hall, 423 Guardian Drive, Philadelphia, PA 19104.

Dr. Mulrow: Annals of Internal Medicine, 190 N. Independence Mall West, Philadelphia, PA 19106.

Ann Intern Med. 2010;152(6):393-395. doi:10.7326/0003-4819-152-6-201003160-00010
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Decision makers often rely on large, multisite observational studies to evaluate the benefits and harms of therapies. An important example is in this issue—a study from Ray and colleagues (1) adds to the debate about the potential harms of concurrent use of proton-pump inhibitors (PPIs) and clopidogrel. These drugs are frequently coprescribed, and the U.S. Food and Drug Administration, primarily on the basis of evidence from multisite observational studies, recently warned against concomitant use of one PPI, omeprazole, and clopidogrel (2). Ray and colleagues' analysis suggests that adverse consequences of concomitant PPI and clopidogrel use are not that clear. In this editorial, we use their data to illustrate techniques for propensity score (PS) adjustment that help address selection bias inherent in multisite observational studies.

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