Dear SAS users, I have been trying to use proc mixed to analyze multivariate crossover data and have been running into a few problems. My dataset takes on the following form for subject 1. Obs id seq period time trt conc 1 1 1 1 1 A 2.23904 2 1 1 1 2 A 2.78095 3 1 1 1 3 A 2.81751 4 1 1 1 4 A 3.08490 5 1 1 1 5 A 2.33377 6 1 1 1 6 A 1.40250 7 1 1 2 1 B 2.19885 8 1 1 2 2 B 3.41063 9 1 1 2 3 B 3.83306 10 1 1 2 4 B 4.07705 11 1 1 2 5 B 3.33320 12 1 1 2 6 B 2.87953 I would like to model the within-subject variances using kronecker products and the code I have been using to analyze this data set is as follows. proc mixed data=mydata; class id period trt time; model conc=period trt time trt*time /solution noint ddfm=kr; repeated period time/type=un@un subject=id r; run; It keeps giving me the error "WARNING: Stopped because of infinite likelihood." I realize after reading the SAS manual that this is because the same subject has the same value for the repeated factors. The error disappears when I add a sequence effect in the model, but my study does not call for its inclusion. It is also a little puzzling that if I use time first and then period, i.e. "repeated time period/type = un@un subject = id r", there are no errors!! Further, this error does not exist when I use un@cs or un@AR(1). Why is this and is there any other way that I could model the within subject variabilites using kronecker products? Thank you in advance for your suggestions and time.
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