Methodological Standards for Meta-Analyses and Qualitative Systematic Reviews of Cardiac Prevention and Treatment Studies: A Scientific Statement From the American Heart Association

Abstract

Meta-analyses are becoming increasingly popular, especially in the fields of cardiovascular disease prevention and treatment. They are often considered to be a reliable source of evidence for making healthcare decisions. Unfortunately, problems among meta-analyses such as the misapplication and misinterpretation of statistical methods and tests are long-standing and widespread. The purposes of this statement are to review key steps in the development of a metaanalysis and to provide recommendations that will be useful for carrying out meta-analyses and for readers and journal editors, who must interpret the findings and gauge methodological quality. To make the statement practical and accessible, detailed descriptions of statistical methods have been omitted. Based on a survey of cardiovascular metaanalyses, published literature on methodology, expert consultation, and consensus among the writing group, key recommendations are provided. Recommendations reinforce several current practices, including protocol registration; comprehensive search strategies; methods for data extraction and abstraction; methods for identifying, measuring, and dealing with heterogeneity; and statistical methods for pooling results. Other practices should be discontinued, including the use of levels of evidence and evidence hierarchies to gauge the value and impact of different study designs (including meta-analyses) and the use of structured tools to assess the quality of studies to be included in a metaanalysis. We also recommend choosing a pooling model for conventional meta-analyses (fixed effect or random effects) on the basis of clinical and methodological similarities among studies to be included, rather than the results of a test for statistical heterogeneity. CLINICAL STATEMENTS AND GUIDELINES D espite the increasing popularity of meta-analyses and systematic reviews in general, problems with methodology are widespread and frequently undermine the credibility of the results. New guidance is needed for both researchers who carry out meta-analyses and systematic reviews in general and the consumers who read them and rely on the results. The term meta-analysis was coined in 1976 by the American statistician Gene Glass, who wrote, "I use it to refer to the statistical analysis of a large collection of results from individual studies for the purpose of integrating findings. It connotes a rigorous alternative to the casual, narrative discussions of research studies which typify our attempts to make sense of the rapidly expanding literature."1 Meta-analyses are a subcategory of the broader category of studies known as systematic reviews.Qualitative systematic reviews include explicit and detailed methods for identification, selection, and grading the quality of individual studies and overall evidence but do not pool results across studies. Meta-analysis is synonymous with the term quantitative systematic review and by definition includes pooling of results across studies. The emphasis in this statement is on metaanalysis bec...

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