Computing Effect Size Measures with ViSta-The Visual Statistics System

Effect size measures are recognized as a necessary complement to statistical hypothesis testing because they provide important information that such tests alone cannot offer. In this paper we: a) briefly review the importance of effect size measures, b) describe some calculation algorithms for the case of the difference between two means, and c) provide a new and easy-to-use computer program to perform these calculations within ViSta The Visual Statistics System . A worked example is also provided to illustrate some practical issues concerning the interpretation and limits of effect size computation. The audience for this paper includes novice researchers as well as ViSta s user interested on applying effect size measures.