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Exercise

The homogeneity of variance assumption

Before you do factorial ANOVA, you need to test the homogeneity of the variance assumption. When studying one-way ANOVA, you tested this assumption with the leveneTest() function.

Since we now have two independent variables instead of just one, the input to leveneTest() changes slightly to: 

leveneTest(dependent_var ~ independent_var1 * independent_var2)
Instructions
100 XP

Test the homogeneity of variance assumption for ab with leveneTest(). Don't save the result; just print it to the console and study the output closely.