The aim of this review is to provide ten appraisal questions that one should ask when reading a meta-analysis (cf., ), although these questions could also be used as simple and accessible guidelines for researchers conducting meta-analyses. For example, recent reviews have revealed that many meta-analyses in ecology and evolution miss, or perform poorly, several critical steps that are routinely implemented in the medical and social sciences (but also see ). As with original research studies, the quality of meta-analyses vary immensely. In contrast to that of many medical and social scientists, the training of a biologist does not typically include meta-analysis and, consequently, it may be difficult for a biologist to evaluate and interpret a meta-analysis. Meta-analysis can not only provide quantitative information (such as overall effects and consistency among studies), but also qualitative information (such as dominant research trends and current knowledge gaps). Chances are, however, that almost all of us have read at least one. It is likely that the majority of us (biologists) have never conducted a meta-analysis. We have argued that the remarkable surge in interest over the last several years may indicate that meta-analysis is superseding traditional (narrative) reviews as a more objective and informative way of summarizing biological topics. Despite this somewhat later arrival, interest in meta-analysis has been rapidly increasing in biological sciences.
Here non-human species, or even ecosystems, are the main focus. Decades later, meta-analysis has infiltrated different areas of biological sciences, including ecology, evolutionary biology, conservation biology, and physiology. Meta-analyses, in which data from multiple studies are combined to evaluate an overall effect, or effect size, were first introduced to the medical and social sciences, where humans are the main species of interest. Last year saw 40 years since the coining of the term ‘meta-analysis’ by Gene Glass in 1976.