The a Priori Procedure for Estimating the Cohen's Effect Size Under Independent Skew Normal Settings.

Cohen’s d is the most popular effect size index for traditional experimental designs, and it is desirable to know the minimum sample size necessary to obtain a sample value that is a good estimate of the population value. The present work addresses that lack with an application to independent samples under the umbrella of skew normal distributions. In addition to derivations of relevant equations, there is a link to a free and user-friendly computer program. Finally, we present computer simulations and a worked example to support the equations and program.