Variables are referred to according to the following conventions:

factor variables

independent variables used to construct the quadratic response surface. To estimate the necessary parameters, each variable must have at least three distinct values in the data. Independent variables must be numeric.

response variables

the dependent variables to which the quadratic response surfaces are fit. Dependent variables must be numeric.

covariates

additional independent variables for use in the regression but not in the formation of the quadratic response surface. Covariates must be numeric.

WEIGHT variable

a variable for weighting the observations in the regression. The WEIGHT variable must be numeric.

ID variables

variables not previously described that are transferred to an output data set containing statistics for each observation in the input data set. This data set is created by using the OUT= option in the PROC RSREG statement. ID variables can be either character or numeric.

BY variables

variables for grouping observations. Separate analyses are obtained for each BY group. BY variables can be either character or numeric.