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(Circulation. 2007;115:2870-2875.)
© 2007 American Heart Association, Inc.

Statistical Primer for Cardiovascular Research

Meta-Analysis

Ton J. Cleophas, MD, PhD; Aeilko H. Zwinderman, DSc, PhD

From the European College of Pharmaceutical Medicine, Lyon, France (T.J.C., A.H.Z.), and Academic Medical Center, Amsterdam, the Netherlands (A.H.Z.).

Correspondence to Ton J. Cleophas, MD, PhD, Department of Medicine, Albert Schweitzer Hospital, Dordrecht, The Netherlands. E-mail ajm.cleophas@wxs.nl

Key Words: population characteristics • meta-analysis • publication bias

An extract of the first 250 words of the full text is provided, because this article has no abstract.

	Introduction

 
In 1982, thrombolytic therapy for acute coronary syndromes was controversial. In a meta-analysis of 7 trials, Stampfer et al¹ found a reduced risk of mortality of 0.80 (95% CI, 0.68 to 0.95). These findings were not accepted by cardiologists until 1986, when a large clinical trial confirmed the conclusions,² and streptokinase became widely applied.

Meta-analyses can be defined as systematic reviews with pooled data. Traditionally, they are post hoc analyses. However, probability statements may be more valid than they usually are with post hoc studies, particularly if performed on outcomes that were primary outcomes in the original trials. Problems with pooling are frequent: Correlations are often nonlinear³; effects are often multifactorial rather than unifactorial⁴; continuous data frequently have to be transformed into binary data for the purpose of comparability⁵; poor studies may be included, and coverage may be limited⁶; and data may not be homogeneous and may fail to relate to hypotheses.⁷ Despite these problems, the methods of meta-analysis are an invaluable scientific activity: they establish whether scientific findings are consistent⁸ and can be generalized across populations and treatment variations⁹ and whether findings vary between subgroups.¹⁰ The methods also limit bias, improve reliability and accuracy of conclusions,¹¹ and increase the power and precision of treatment effects and risk exposures.⁶

The objective of this article is to review statistical procedures for the meta-analysis of cardiovascular research. The Google database system provides 659 000 references on the methods of meta-analysis and refers to hundreds of books of up . . . [Full Text of this Article]

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