Effect-Size Indices for Dichotomized Outcomes in Meta-Analysis

Sánchez-Meca, Julio
Marín-Martínez, Fulgencio
Chacón-Moscoso, Salvador

¹Department of Basic Psychology and Methodology, University of Murcia, Murcia, Spain
²Department of Psychology, University of Seville, Seville, Spain.

³Correspondence concerning this article should be addressed to Julio Sánchez-Meca, Department of Basic Psychology and Methodology, Faculty of Psychology, Campus of Espinardo, University of Murcia, P.O. Box 4021, 30100 Murcia, Spain. E-mail: [email protected].

This article was supported by a grant from the Ministerio de Ciencia y Tecnología and by funds from the Fondo Europeo de Desarrollo Regional (FEDER; Project Number BSO2001-0491). We gratefully acknowledge William R. Shadish and Mark W. Lipsey for their helpful suggestions on a first draft of this article. We also thank the referees for comments that greatly improved the manuscript.

Received August 30, 2002; Revision received March 25, 2003; Accepted July 18, 2003

Psychological Methods 8(4):p 448-467, December 2003.

It is very common to find meta-analyses in which some of the studies compare 2 groups on continuous dependent variables and others compare groups on dichotomized variables. Integrating all of them in a meta-analysis requires an effect-size index in the same metric that can be applied to both types of outcomes. In this article, the performance in terms of bias and sampling variance of 7 different effect-size indices for estimating the population standardized mean difference from a 2 × 2 table is examined by Monte Carlo simulation, assuming normal and nonnormal distributions. The results show good performance for 2 indices, one based on the probit transformation and the other based on the logistic distribution.