crossover design

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crossover design

Hello everyone,

I have a data on a 3 way cross over design with two treatments(A and B, B is given twice) applied on 16 subjects in three different periods using three sequences. So i have analyzed it using Proc mixed procedure in SAS 9.1 given below:

PROC MIXED data=data ;
CLASSES SEQ SUB PER TRT;
MODEL Y=SEQ PER TRT /DDFM=SATTERTH;
RANDOM TRT/TYPE=FA0(2) SUB=SUB G;
REPEATED/GRP=TRT SUB=SUB;
LSMEANS TRT;
ESTIMATE 'T vs. R' TRT 1-1/CL ALPHA=0.1;

Now in output, residual value is coming for both treatments A and B in Covariance parameter estimate while B is the only treatment repeated. So my question is how am i getting residual value for both the treatments. Is it correct or there is some problem with my SAS codes.

Looking forward for your valuable comments.

Regards,
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