A second caveat is that effect size measures other than Cohen’s f 2 may be appropriate for similar analyses. Previous literature has suggested as a local effect size the proportional reduction in variance (PRV) after the variable of interest has been added to a mixed-effects model or hierarchical linear model, compared to an A-only model (Peugh, 2010). PRV is related to Cohen’s f 2 through R2-type measures, but has disadvantages for these particular current research questions. Specifically, PRV does not incorporate the total variance of the model prior to adding regressors, thus a given value of PRV may indicate different effect sizes relative to the overall model, depending on the variance of the intercept-only model. As a result, Cohen’s f 2 is standardized with respect to the total variance, allowing more accurate comparison of effect sizes between variables within the model as a whole.
