DIRECT Statement

The CATMOD Procedure

DIRECT Statement

DIRECT variables ;

The DIRECT statement lists numeric independent variables to be treated in a quantitative, rather than qualitative, way. The DIRECT statement is useful for logistic regression, which is described in the "Logistic Regression" section. For limitations of models involving continuous variables, see the "Continuous Variables" section.

If specified, the DIRECT statement must precede the MODEL statement. For example,

   proc catmod;
      direct X;
      model Y=X;
   run;

Suppose X has five levels. Then the main effect X induces only one column in the design matrix, rather than four. The values inserted into the design matrix are the actual values of X.

You can interactively change the variables declared as DIRECT variables by using the statement without listing any variables. The following statements are valid:

   proc catmod;
      direct X;
      model Y=X;
      weight wt;
   run;
      direct;
      model Y=X;
   run;

The first MODEL statement uses the actual values of X, and the second MODEL statement uses the four variables created when PROC CATMOD generates the design matrix. Note that the preceding statements can be run without a WEIGHT statement if the input data are raw data rather than cell counts.

For more details, see the discussions of main and direct effects in the section "Generation of the Design Matrix".

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