Typically, but not necessarily, the study is based on randomized, controlled clinical trials. Meta-analysis is a quantitative, formal, epidemiological study design used to systematically assess the results of previous research to derive conclusions about that body of research. Glass first defined meta-analysis in the social science literature as "The statistical analysis of a large collection of analysis results from individual studies for the purpose of integrating the findings" 9.
#Publication bias in comprehensive meta analysis series
In contrast, animal research, laboratory studies, case series and case reports have little clinical value as proof, hence being in the bottom.
In fact, in the hierarchy of evidence ( Figure 1), where clinical evidence is ranked according to the strength of the freedom from various biases that beset medical research, meta-analyses are in the top. Therefore, meta-analysis, a statistical procedure that integrates the results of several independent studies, plays a central role in evidence-based medicine. Evidence-based medicine may be defined as the systematic, quantitative, preferentially experimental approach to obtaining and using medical information. The need to arrive at decisions affecting clinical practise fostered the momentum toward "evidence-based medicine" 1 – 2.
In many instances, the results of these multiple small studies of an issue are diverse and conflicting, which makes the clinical decision-making difficult. Important medical questions are typically studied more than once, often by different research teams in different locations. The need to integrate findings from many studies ensures that meta-analytic research is desirable and the large body of research now generated makes the conduct of this research feasible. Rigorously conducted meta-analyses are useful tools in evidence-based medicine. A failure to identify the majority of existing studies can lead to erroneous conclusions however, there are methods of examining data to identify the potential for studies to be missing for example, by the use of funnel plots. The specification of the outcome and hypotheses that are tested is critical to the conduct of meta-analyses, as is a sensitive literature search.
The benefits of meta-analysis include a consolidated and quantitative review of a large, and often complex, sometimes apparently conflicting, body of literature. The examination of variability or heterogeneity in study results is also a critical outcome. Outcomes from a meta-analysis may include a more precise estimate of the effect of treatment or risk factor for disease, or other outcomes, than any individual study contributing to the pooled analysis. Meta-analysis is a quantitative, formal, epidemiological study design used to systematically assess previous research studies to derive conclusions about that body of research. Methods used to produce a rigorous meta-analysis are highlighted and some aspects of presentation and interpretation of meta-analysis are discussed. The objectives of this paper are to provide an introduction to meta-analysis and to discuss the rationale for this type of research and other general considerations.
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