The USERDEFINED statement is used to identify the variables in the input data set or auxiliary data set that are available for user-defined regression. Only numeric variables can be specified. Specifying variables in the USERDEFINED statement does not include the variables as regressors. If a variable is specified in the INPUT statement or USERVAR= option in the REGRESSION statement, it is not necessary to include that variable in the USERDEFINED statement. However, if a variable is specified in the MDLINFOIN= data set in the PROC X12 statement and is not specified in an INPUT statement or in the USERVAR= option in the REGRESSION statement, then the variable should be specified in the USERDEFINED statement in order to make the variable available for regression.