Exam 15: Group Research Design and Statistical Analyses

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Meta-analysis is the practice of combining the results of several studies and analyzing the pooled data in order to quantify the overall effect(s) of a particular independent variable on some common outcome measure or measures. Effect sizes are usually calculated for each study, aggregated across all studies, and analyzed statistically. Meta-analysis has several benefits. A good meta-analysis synthesizes the reported results of multiple studies in a particular area and quantifies them in ways that are not typical of other types of research reviews. That can save practitioners, researchers, and policymakers the time and effort of combing the research literature and digesting and integrating the findings of large numbers of studies. Another is that meta-analyses often result in large sample sizes, which enable some types of analyses and general conclusions that could not be derived from individual studies. The methods may be particularly useful for examining the effects of treatments that have been evaluated with relatively small samples of participants because the treatments are complex or target relatively rare conditions, for example. Additionally, combining measures from all studies weights evenly the contributions of small and large studies. In sum, meta-analyses can be useful for determining the best available evidence about a particular treatment, the overall comparative effectiveness of treatments, and the conditions under which a treatment is effective and with whom.