Why Cohen’s effect size rule should be avoided

From Durlak (2009), How to select, calculate, and interpret effect sizes: Many authors still routinely refer to Cohen’s (1988) comments made in reference to power analysis that SMDs of 0.20 are “small” in magnitude, those around 0.50 are “medium” and those around or above 0.80 are “large.” In terms of r, Cohen suggested corresponding figures of…