Each design variable is used with the other design variables. The first design variable is the linear component, the second is the quadratic, etc. Use ORTH for ordered categories. Unavailable for covariates with more than 11 categories. Specify terms included in the model.
Interaction means product for interval-scaled variables.
PR adds a constant term to the model. Specify the rule for entering and removing variables and variable interactions. Requests a singularity check at each iteration to control numerical accuracy. Computations are performed in double precision. Specify value of convergence criterion for the likelihood function.