standardized mean difference Cohen's d COKA/SEVCO Expert Working Group Agreement: 2022-07-20 vote 5-0 by Philippe Rocca-Serra, Mario Tristan, Jesus Lopez-Alcalde, Harold Lehmann, Eric Harvey A standardized mean difference which is calculated as a difference between two means, divided by a square root of an average of the variances of the two groups. In Cohen's d statistic, the statistical measure of dispersion is specified as the square root of an average of the variances of the two groups being compared. The variances of the two groups are based on within-group standard deviations. For sample sizes < 50, a correction factor is used. Harold Lehmann, Brian S. Alper, Kenneth Wilkins, Muhammad Afzal, Joanne Dehnbostel ready for release