Recall that one-factor ANOVA lets you compare several groups but allows only 1 factor or IV. Sometimes you want to look at the effects of two or more factors or IVs. For that we use a Factorial ANOVA (with multiple IVs and 1 DV) We will just use two factors today - that's enough! - The goal of the two-factor ANOVA is to evaluate the mean differences that may be produced by two factors acting independently or by two factors acting together. The mean differences among the levels of one factor are referred to as the main effect of that factor. An Interaction occurs whenever the effects of the two treatment conditions combine in a way that is different from adding the main effects of the factors separately. For example effects of A depend on level of B