CLASS Statement
When should I put a variable in the CLASS statement? What does the CLASS statement do? The CLASS statement is used to indicate which variables in the model are categorical variables. In most modeling procedures, such a variable is then treated as a nominal (unordered) categorical predictor variable. A set of numeric indicator ("dummy") variables is created internally to represent the levels of the variable. Because the indicator variables are used for fitting the model, the original variable does not need to be numeric. The resulting model has multiple parameter estimates (one for each indicator variable). Each parameter compares one level of the predictor with a reference level, typically the last level in sorted order. A joint test of all the estimated parameters for the predictor is a test for any differences among the levels and is therefore a test of the predictor's overall effect. In contrast, a variable name that appears in the MODEL statement but not in the CL...