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 deciles_interaction_plot and 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.
Deciles interaction plot
The function
The function in use
Sextiles interaction plot
The function
The function in use
References
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
Pablo Bernabeu
Postdoctoral fellow at UiT –
The Arctic University of Norway
After doing a research master's, I became a PhD student and graduate teaching assistant in Psychology at Lancaster University, where I investigated how conceptual processing—that is, the comprehension of the meaning of words—is supported by linguistic and sensorimotor brain systems, and how research on this topic is influenced by methodological aspects such as the operationalisation of variables and the sample size of experiments. Currently, I am a postdoctoral fellow at UiT The Arctic University of Norway, where I am investigating the behavioural and neural underpinnings of multilingualism. Throughout my research, I have used methods such as behavioural and electroencephalographic experiments, corpus analysis, statistics and programming. Research materials at https://osf.io/25u3x. CV available here.