title: An alternative to Cohen's standardized mean difference effect size: a robust parameter and confidence interval in the two independent groups case.
abstract: The authors argue that a robust version of Cohen's effect size constructed by replacing population means with 20% trimmed means and the population standard deviation with the square root of a 20% Winsorized variance is a better measure of population separation than is Cohen's effect size. The authors investigated coverage probability for confidence intervals for the new effect size measure. The confidence intervals were constructed by using the noncentral t distribution and the percentile bootstrap. Over the range of distributions and effect sizes investigated in the study, coverage probability was better for the percentile bootstrap confidence interval.
authors.affiliation: Department of Educational Psychology, University of Florida, Gainesville, FL 32611-7047, USA. algina@ufl.edu
authors.forename: James
authors.initials: J
authors.lastname: Algina
authors.forename: H J
authors.initials: HJ
authors.lastname: Keselman
authors.forename: Randall D
authors.initials: RD
authors.lastname: Penfield
mesh_terms: D000704:Analysis of Variance; D016001:Confidence Intervals; D003625:Data Collection / Q000706:statistics & numerical data*; D003627:Data Interpretation, Statistical; D003710:Demography; D015987:Effect Modifier, Epidemiologic; D006801:Humans; D015233:Models, Statistical; D016011:Normal Distribution; D011336:Probability; D013223:Statistics as Topic