The CLASS statement specifies the classification variables to be used in the model. Typical classification variables are TREATMENT, GENDER, RACE, GROUP, and REPLICATION. If you specify the CLASS statement, it must appear before the MODEL statement.

Classification variables can be either character or numeric. Class levels are determined from the formatted values of the CLASS variables. Thus, you can use formats to group values into levels. See the FORMAT procedure in the Base SAS Procedures Guide and the FORMAT statement and SAS formats in SAS Language Reference: Dictionary for more information.

By default, class levels are determined from the entire formatted values of the CLASS variables. Note that this represents a slight change from previous releases in the way in which class levels are determined. Prior to SAS 9, class levels were determined by using no more than the first 16 characters of the formatted values. If you want to revert to this previous behavior, you can use the TRUNCATE option in the PROC SURVEYREG statement.

You can use multiple CLASS statements to specify classification variables.