title: A measure of effect size for experimental designs with heterogeneous variances.
abstract: A recent trend in the psychological literature has been to include measures of effect size when reporting probability values. The several measures of effect size associated with the Student t test for two independent samples are appropriate only when the variances are homogeneous. In this paper, commonly used measures of effect size are considered and compared, using four data sets. A chance-corrected measure of effect size is provided for two or more treatment groups characterized by either homogeneous or heterogeneous variances.
authors.affiliation: Department of Sociology, Colorado State University, Fort Collins, CO 80523-1784, USA. janisj@lamar.colostate.edu
authors.forename: Janis F
authors.initials: JF
authors.lastname: Johnston
authors.forename: Kenneth J
authors.initials: KJ
authors.lastname: Berry
authors.forename: Paul W
authors.initials: PW
authors.lastname: Mielke
mesh_terms: D015987:Effect Modifier, Epidemiologic; D006801:Humans; D008960:Models, Psychological; D012107:Research Design