In my opinion, PARAM=GLM and PARAM=REF were both sides of the same kind of parametrization. Both provide comparisons to a reference level ; the only differences are :
- you cannot choose the reference level with PARAM=GLM, it is always the last formatted value in alphabetic order that is chosen as reference ;
- you will not see the zeroed coefficient for the reference with PARAM=REF.
I prefer to use PARAM=GLM to show that explicit zero, and use a format to re-order my values and have the reference be the last one.
Also useful, PARAM=EFFECT compares to overall mean ; that means that all coefficients for a variables sum to zero. This is nice since it avoids the problem of choosing a meaningful reference ; but it does not display the last coefficient either, as PARAM=REF does, so you have to compute it by yourself.
On my computer (SAS 9.1.3 SP4), this code
proc genmod data=genmodtest;
class b_a(param=ref) orientdeg(param=effect) ;
model freq_a/n_ab=b_a orientdeg /noint ;
run;
gives mixed parametrization without error.
I dunno if it solves your problem, but I hope it is of any help.
Olivier
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