A new generation of statistical methods of research synthesis were first introduced into ecology 20 years ago. These methods, known collectively as meta-analysis, were originally developed in the social sciences and medicine in the late 1970s, and provide a powerful, informative and objective set of tools for summarizing the results of studies on the same topic. Meta-analyses generally work by transforming the outcome of each study into a “common currency”, a standardized measure of the sign and magnitude of an effect of interest in each study. |