Decomposing interactions using GLM in combination with the COMPARE, LMATRIX and MMATRIX subcommands in SPSS

In this tutorial, we provide researchers who use SPSS step-by-step instructions for decomposing interactions when a three-way ANOVA is conducted using the GLM procedure. We start with a demonstration of how a two-way interaction can be decomposed using the COMPARE subcommand in combination with syntax. Then, we provide instructions with examples for conducting simple interaction and secondorder simple effects analyses for three-way ANOVAs with between-subjects, withinsubjects, and mixed between-and within-subjects variables using the LMATRIX or MMATRIX subcommands. Provided in Appendices are general rules that can be used to derive design-specific LMATRIX and MMATRIX subcommands.