SAS

Reporting effect sizes in scientific articles is increasingly widespread and encouraged by journals; however, choosing an effect size for analyses such as mixed-effects regression modeling and hierarchical linear modeling can be difficult. One relatively uncommon, but very informative, standardized measure of effect size is Cohen’s f2, which allows an evaluation of local effect size, i.e., one variable’s effect size within the context of a multivariate regression model. Unfortunately, this measure is often not readily accessible from commonly used software for repeated-measures or hierarchical data analysis. In this guide, we illustrate how to extract Cohen’s f2 for two variables within a mixed-effects regression model using PROC MIXED in SAS® software. Two examples of calculating Cohen’s f2 for different research questions are shown, using data from a longitudinal cohort study of smoking development in adolescents. This tutorial is designed to facilitate the calculation and reporting of effect sizes for single variables within mixed-effects multiple regression models, and is relevant for analyses of repeated-measures or hierarchical/multilevel data that are common in experimental psychology, observational research, and clinical or intervention studies.

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Current studies assessing sexual assertiveness in drug users are sparse, despite the fact that it would be logical to expect low sexual assertiveness in such patients. Present study had the objective to compare sexual assertiveness between consumers of alcohol, cocaine, cocaine+alcohol, heroin, cannabis, and speedball and a control group. This was assessed in a sample of 556 male drug users from 8 Spanish provinces and 356 non-user males. Results showed significantly lower Initiation assertiveness in the 35-49 year-old age group (particularly in the case of alcohol, heroin, cannabis, and speedball) and worse Sexually Transmitted Diseases and Pregnancy prevention assertiveness in drug users (in the case of alcohol, cocaine, cocaine+alcohol, cannabis, and speedball). Effect sizes ranged from low to moderate. The implications of these results are discussed.