APA Dictionary of Psychology

an effect size measure that represents the standardized difference between means (i.e., the difference in average values for two samples divided by the standard deviation of the second sample). It is often used in meta-analysis and other research in which it is important to determine whether an effect persists across studies in order to consolidate a result. Also called Glass’s delta. See also Cohen’s d; Hedges’s g. [Gene V. Glass (1940–  ), U.S. statistician]