The BTL Procedure (Experimental)
CLASS variables ;
The CLASS statement names the classification variables to be used in the analysis. If the CLASS statement is used, it must appear before the MODEL statement.
Classification variables can be either character or numeric. By default, class levels are determined from the entire formatted values of the CLASS variables. You can use formats to group values into levels. See the discussion of the FORMAT procedure in the Base SAS Procedures Guide and the discussions of the FORMAT statement and SAS formats in SAS Language Reference: Dictionary. You can adjust the order of CLASS variable levels by using the ORDER= option in the PROC BTL statement.
You can specify the following option in the CLASS statement after a slash (/):