What is SAS’s default reference group for categorical variables in regression analysis in proc GLM?

[bhr-q]

When we perform regression analysis with categorical independent variables in SAS, if I let SAS choose the reference group, what is the default setting for that? 

I know the sas code

Thanks,

[StatDave]

It uses the last level when internally sorted in alphanumeric order. So, with levels A, B, and C, it will use C as the reference level.

[bhr-q]

Thanks so much for your answer, is there any way to set the reference category in proc GLM by ourselves?

[PaigeMiller · Accepted solution]

Example:

proc glm data=sashelp.class;
class sex(ref='F');
model height=sex weight age;
run; quit;

Documentation for the CLASS statement in PROC GLM

https://documentation.sas.com/doc/en/pgmsascdc/9.4_3.4/statug/statug_glm_syntax04.htm

[bhr-q]

Thanks a lot