Plotting two-way interactions from mixed-effects models using ten or six bins
Whereas the direction of main effects can be interpreted from the sign of the estimate, the interpretation of interaction effects often requires plots. This task is facilitated by the R package
sjPlot (Lüdecke, 2022). In Bernabeu (2022), the sjPlot function called
plot_model served as the basis for the creation of some custom functions. Two of these functions are
sextiles_interaction_plot. These functions allow the plotting of interactions between two continuous variables. In the case of
deciles_interaction_plot, one of the variables is divided into ten bins, known as deciles, and the other variable is unchanged. In the case of
sextiles_interaction_plot, one of the variables is divided into six bins, or sextiles, and the other variable is unchanged.
Below, we’ll use these functions with models fitted using
lmerTest (Kuznetsova et al., 2022), although the functions also work with several other models (see sjPlot manual). The plots can be reproduced using the materials at https://osf.io/gt5uf.
Sextiles interaction plot
Bernabeu, P. (2022). Language and sensorimotor simulation in conceptual processing: Multilevel analysis and statistical power. Lancaster University. https://doi.org/10.17635/lancaster/thesis/1795
Kuznetsova, A., Brockhoff, P. B., & Christensen, R. H. B. (2022). Package ’lmerTest’. CRAN. https://cran.r-project.org/web/packages/lmerTest/lmerTest.pdf
Lüdecke, D. (2022). Package ’sjPlot’. CRAN. https://cran.r-project.org/web/packages/sjPlot/sjPlot.pdf