Calculation of a distribution free estimate of effect size and confidence intervals using VBA/Excel

Abstract

Reporting effect sizes aids the transparent presentation and independent interpretation of scientific data. However, calculation and reporting of effect sizes for data obtained in basic research is rare. A standardized effect size was reported by Norman Cliff, known as Cliff's delta. It has several advantageous features, as (i) it makes no assumption on the shape of the underlying distribution, (ii) it works well for small to moderate samples (n>10), (iii) it is easy to calculate, and (iv) its basis is readily understood by non statisticians. Here, a VBA macro, implemented in Excel, is presented. The macro takes two independent samples as input and calculates Cliff's delta with 95% confidence intervals. The macro will reduce the barrier for calculating the effect size and can be a valuable tool for research and teaching.