The PROC MIXED procedure in SAS software is used in this guide, as it is a powerful and widely used tool for running mixed-effects regression models and hierarchical linear models. It is important to note that PROC MIXED assumes the dependent variable to be continuous and approximately normally distributed; thus, the calculations described in the examples below are for continuous dependent variables. As the calculation for Cohen’s f 2 is based on R2 values of different versions of the full regression model, it is necessary to extract R2 from the output of PROC MIXED in SAS. Though R2 is not output directly, it is the proportion of variance accounted for by the regressors in the model and can thus be calculated using the residual variance of the full model (Vfull) and the residual variance of the model with no regressors (Vnull):
