Extension of Nakagawa & Schielzeth's R2GLMM to random slopes models

Nakagawa & Schielzeth extended the widely used goodness-of-fit statistic R-2 to apply to generalized linear mixed models (GLMMs). However, their R-GLMM(2) method is restricted to models with the simplest random effects structure, known as random intercepts models. It is not applicable to another common random effects structure, random slopes models. I show that R-GLMM(2) can be extended to random slopes models using a simple formula that is straightforward to implement in statistical software. This extension substantially widens the potential application of R-GLMM(2).