A unified approach to measuring the effect size between two groups using SAS

Abstract

Standardized difference scores are intuitive indexes which measure the effect size between two groups. Compared to a t-test or Wilcoxon rank-sum test, they are independent of sample size. Thus, their use can be recommended for comparing baseline covariates in clinical trials as well as propensity-score matched studies. In this paper, we show how to calculate sample standardized differences for continuous and categorical variables and how to interpret results. We also provide a SAS macro which performs the calculation without using the IML procedure.