Meta-analysis: Potentials and promise -- Egger and Smith 315 (7119): 1371 -- BMJ

Top Introduction Historical notes The unacceptable face of... Narrative reviews Limitations of a single... Epidemiology of results A more transparent appraisal Cumulative meta-analysis References The number of papers published on meta-analyses in medical research has increased sharply in the past 10 years (fig 1). The merits and perils of the somewhat mysterious procedure of metaanalysis, however, continue to be debated in the medical community. 2 3 What, then, is metaanalysis? A useful definition was given by Huque: "A statistical analysis that combines or integrates the results of several independent clinical trials considered by the analyst to be 'combinable.'" 4 The terminology, however, is still debated, and expressions used concurrently include "overview," "pooling," and "quantitative synthesis." We believe that the term metaanalysis should be used to describe the statistical integration of separate studies, whereas "systematic review" is most appropriate for denoting any review of a body of data that uses clearly defined methods and criteria (box). Systematic reviews can include meta-analyses, appraisals of single trials, and other sources of evidence. In this article we examine the potentials and promise of meta-analysis of randomised controlled trials. In later articles of this series we will consider the practical steps involved in meta-analysis, examine various extensions beyond the calculation of a combined estimate, address potential biases and discuss strategies to detect and minimise the influence of these in meta-analysis of randomised trials and of observational studies. We will conclude with a discussion of unresolved issues and future developments. Details of