Programming the statistical procedures from SAS

Proc mixed level 2 variable

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Proc mixed level 2 variable

I have two separate clinical trial datasets that have the same variables and sites are numbered consecutively for each clinical trial.  I have combined both clinical trials into one dataset using the set statement.  I also have a flag for each clinical trial.  I have a unique subject id that is unique across both clincial trial datasets.  I am clustering patients within sites.  The sites ids are the same in many cases across both clinical trials.  Is that a problem with proc mixed and using siteid as the clustering variable?  Does siteid need to be unique in the combined dataset eventhough the patient id is unique?  I have a feeling it is, but wanted to confirm.

 

I used the following code: 

 

proc mixed data=analysisaim1 covtest method=ML order=data;
class siteid;
model chgql=trial racecat cntrycat totcomorbid suppcare ecogb NumPt trtdur/solution ddfm=kr;
random intercept/subject=siteid;
run;

 

I am using SAS 9.4 TS.  Any help you could provide would be greatly appreciated.  Thanks.

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Valued Guide
Posts: 684

Re: Proc mixed level 2 variable

The side IDs should be unique for the nesting you describe. Easy to handle. First, trial should be listed in the class statement (I can't imagine how trial is a continuous variable). then in the random statement, use subject=siteid(trial);

Contributor
Posts: 49

Re: Proc mixed level 2 variable

Thank you for your help with this. I had copied and pasted from my code but did not copy the class statement properly. Trial is a categorical variable and not a continuous variable. I do have trial in my class statement. That is a pretty easy fix. I will try that. Thank you for your help.
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