Programming the statistical procedures from SAS

PROC GLIMMIX and MIXED basic questions

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Regular Contributor
Posts: 180

PROC GLIMMIX and MIXED basic questions

Hello all,

I have some basic questions regarding PROC GLIMMIX and PROC MIXED, and probably other mixed models related PROC's.

Assume that I have an outcome variable Y, continuous, and a treatment variable X with 2 levels. Let's also say that every subject in the analysis contributes 3 data points (can be 3 treatments in one person, or students within schools).

If I write this code:

proc mixed data = ....;

     class SubjID;

     model Y = X / solution cl;

     [random statement]    

run;

what is the difference between:

random SubjID;

to

random intercept / subject = SubjID;

and let's say (if it's a legal statement):

random Treatment / subject = SubjID;

I tried it on a small data set and the first two options gave me identical results. This question of course is relevant also for glimmix with a dist = binary.

And one more question, if I have this scenario, and I run a PROC MIXED once with random statement and once with REPEATED, and the results are very similar and leading to the same conclusions, how can I choose if to use R side or G side covariance ?

Thank you !

Respected Advisor
Posts: 2,655

Re: PROC GLIMMIX and MIXED basic questions

A really valuable source is SAS for Mixed Models, 2nd ed. by Littell et al.  I can't imagine working with SAS and mixed models without having this available.

And it will answer every one of your questions that you posed.

Steve Denham

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