Effect Size, Measures of

Effect size is a statistical term for the measure of associations between two variables. It is widely used in many study designs, such as meta-analysis, regression, and analysis of variance (ANOVA). The presentations of effect size in these study designs are usually different. For example, in meta-analysis—an analysis method for combining and summarizing research results from different studies—effect size is often represented as the standardized difference between two continuous variables’ means. In analysis of variance, effect size can be interpreted as the proportion of variance explained by a certain effect versus total variance. In each study design, due to the characteristic of variables, say, continuous versus categorical, there are several ways to measure the effect size. This entry discusses the measure of effect size by ...