In Chapters 17 and 18, regression analysis was presented for designs with continuous independent variables. The present chapter is devoted to the application of regression analysis in designs with a categorical independent variable. Recall that a categorical variable consists of two or more mutually exclusive and exhaustive categories (e.g., treatments, marital status; see, for example, Chapters 2 and 8). Application of regression analysis in designs with more than one categorical variable is presented in the next chapter. At the conclusion of this and the next chapter, we comment on the equivalence between the approach we are presenting and the analysis of variance (ANOYA).