ABSTRACT
The one-way and repeated measures analysis of variances (ANOVA) tests covered in Chapter 11 were single factor tests: the one-way ANOVA analysed the influence of a between-subjects factor while the repeated measures ANOVA analysed the influence of a within-subjects factor. The current chapter covers the purpose and use of ANOVA tests that include more than one factor. These are sometimes referred to as factorial ANOVA tests or multifactor ANOVA tests. These tests allow conclusions to be drawn about the effect of more than one factor on some numerical dependent variable. There are benefits to using a factorial ANOVA test instead of using a single factor ANOVA test for each factor of interest. The first benefit is that the factorial ANOVA test will not only analyse the effect of the individual factors (main effects), but will also analyse the combined effect of the factors (interaction effects). An interaction effect exists where the effect of one factor differs for the different levels of some other factor(s).
