PROC LOGISTIC DATA=gator;
  CLASS Food(REF="fish" PARAM=REF) Size(Ref="small" PARAM=REF) Lake(REF="George" PARAM=REF);
  MODEL Food = Size Lake / LINK=GLOGIT;
RUN;

PROC LOGISTIC DATA=gator;
  CLASS Food(REF="invert" PARAM=REF) Size(Ref="small" PARAM=REF) Lake(REF="George" PARAM=REF);
  MODEL Food = Size Lake / LINK=GLOGIT;
RUN;