ABSTRACT
Cohen's d is so widely used as a measure of effect size that some researchers use the term effect size and d interchangeably—as though they are synonyms. However, effect size refers to any statistic that describes the size of a difference on a standardized metric. In addition to d, a number of other measures of effect size have been proposed. One that is very widely reported is effect-size r, which is simply the Pearson correlation coefficient (r). In basic studies, the choice between reporting means and the associated values of d and reporting correlation coefficients and the associated values of r2 is usually quite straightforward. If a researcher wants to determine which of two groups is superior on average, a comparison of means using d is usually the preferred method of analysis. There are also additional online resources for learning how to compute effect size statistics.
