Meta-analysis: How it came about, and the latest in “the science of research synthesis”

An essential part of “the scientific process” is to synthesize results across studies to reach an overall understanding of a problem and to identify sources of variation in outcomes. Before ~1978, the results of scientific studies have been summarized in narrative reviews; however, this approach becomes inadequate when there are hundreds of studies ona given research question. Also, the difficulties of carrying out narrative reviews to identify and summarize evidence in a transparent and objective manner have become increasingly apparent as research results have exploded across many scientific fields.

During the past 3-4 decades, scientifically rigorous systematic reviews and meta-analyses –– carried out following formal protocols to ensure reproducibility and reduce bias –– have become more prevalent in a range of fields [see attached article, an excellent REVIEW]. Systematic reviews aim to provide a robust overview of the efficacy of an intervention, or of a problem or field of research; they can be combined with quantitative meta-analyses to assess the magnitude of the outcome across relevant primary studies and to analyse the causes of variation among study outcomes (effect-sizes).

Whereas the number of published meta-analyses has continued to increase rapidly, too many meta-analyses and systematic reviews are of low quality, as detailed in the attached review. Since the term META-ANALYSIS and modern approaches to research synthesis were first introduced in the 1970s, meta-analysis has had a revolutionary effect in many scientific fields, helping to establish evidence-based practice and to resolve seemingly contradictory research outcomes. At the same time, its implementation has engendered criticism and controversy, in some cases general, and in other cases specific to particular disciplines. Herein the authors take the opportunity provided by the recent 40th anniversary of meta-analysis to reflect on –– its accomplishments, limitations, recent advances, and predicted directions for future developments in this field of research synthesis.

Nature 8 Mar 2o18; 555: 175–182

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