There are multiple ways to paramaterize class variables. You can change the paramaterization in the CLASS statement with the PARAM option.
e.g.:
PROC GENMOD data=data;
class treatment / param=X;
model outcome = treatment;
run;
where X is any of the options detailed here (e.g. ref, effect, glm, etc.). The default is the glm parameterization:
PROC GENMOD: CLASS Variable Parameterization
You can also use the REF option to specify the reference level.
e.g.:
PROC GENMOD data=data;
class treatment(ref='Control');
model outcome = treatment;
run;
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