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A primary goal of meta-analysis is to improve the estimation of treatment effects by pooling results of similar studies. This article explains how the most widely used method for pooling heterogeneous studies—the DerSimonian–Laird (DL) estimator—can produce biased estimates with falsely high precision. A classic example is presented to show that use of the DL estimator can lead to erroneous conclusions. Particular problems with the DL estimator are discussed, and several alternative methods for summarizing heterogeneous evidence are presented. The authors support replacing universal use of the DL estimator with analyses based on a critical synthesis that recognizes the uncertainty in the evidence, focuses on describing and explaining the probable sources of variation in the evidence, and uses random-effects estimates that provide more accurate confidence limits than the DL estimator.
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Author, Article, and Disclosure Information
From University of Texas Health Science Center at San Antonio, San Antonio, Texas; University of Pennsylvania and American College of Physicians, Philadelphia, Pennsylvania; Johns Hopkins School of Public Health, Baltimore, Maryland; and Stanford University School of Medicine, Stanford, California.
Disclosures: Disclosures can be viewed at www.acponline.org/authors/icmje/ConflictOfInterestForms.do?msNum=M13-2886.
Corresponding Author: John E. Cornell, PhD, Department of Epidemiology and Biostatistics, University of Texas Health Science Center at San Antonio, 7703 Merton Minter Boulevard, San Antonio, TX 78229; e-mail, [email protected]
Current Author Addresses: Dr. Cornell: Department of Epidemiology and Biostatistics, University of Texas Health Science Center at San Antonio, 7703 Merton Minter Boulevard, San Antonio, TX 78229.
Dr. Mulrow: University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, San Antonio, TX 78229.
Dr. Localio: Center for Clinical Epidemiology and Biostatistics, University of Pennsylvania, 635 Blockley Hall, 423 Guardian Drive, Philadelphia, PA 19104-6021.
Drs. Stack and Meibohm: American College of Physicians, 190 N. Independence Mall West, Philadelphia, PA 19106.
Dr. Guallar: Welch Center for Prevention, Epidemiology and Clinical Research, Johns Hopkins Medical Institutions, 2024 East Monument Street, Room 2-645, Baltimore, MD 21287.
Dr. Goodman: Stanford University School of Medicine, 259 Campus Drive, T265 Redwood Building/HRP, Stanford, CA 94305.
Author Contributions: Conception and design: J.E. Cornell, C.D. Mulrow, R. Localio, S.N. Goodman.
Analysis and interpretation of the data: J.E. Cornell, R. Localio.
Drafting of the article: J.E. Cornell, C.D. Mulrow, R. Localio, C.B. Stack, A.R. Meibohm, S.N. Goodman.
Critical revision of the article for important intellectual content: J.E. Cornell, C.D. Mulrow, R. Localio, C.B. Stack, A.R. Meibohm, E. Guallar, S.N. Goodman.
Final approval of the article: J.E. Cornell, C.D. Mulrow, R. Localio, C.B. Stack, A.R. Meibohm, E. Guallar, S.N. Goodman.
Statistical expertise: J.E. Cornell, R. Localio, A.R. Meibohm, S.N. Goodman.
Administrative, technical, or logistic support: C.D. Mulrow.
Collection and assembly of data: J.E. Cornell.

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