This article first explains the choice of Cohen’s f 2 as a useful measure of local effect size appropriate for hierarchical and repeated-measures data. Next, a step-by-step guide is provided for calculating Cohen’s f 2 from PROC MIXED in SAS software, a popular and powerful tool for mixed-effects regression models and hierarchical linear models. Finally, using data from a longitudinal cohort study of adolescent smoking to compare local effect sizes of separate variables, two examples are given in which Cohen’s f 2 is calculated to answer variants of this research question.
