Well, I may have led you down something of a blind alley here.  When fitting an R side covariance structure, some structures "build in" a random subject effect.  Three prominent members of this group are CS, CSH and UN.   Try fitting: proc mixed data=test; class AOI Spray View Sex StimulusIdentity Subject Trial; model RatioOfTotalDwellTime=AOI Spray View AOI*Spray AOI*Spray*View Sex StimulusIdentity; repeated AOI / subject=Subject*Trial type=cs; lsmeans AOI*Spray / diff; where aoi < 4; run; and see if the results are more easily interpreted.  The point is that in a repeated measurement context, correlations within subject and between subject are accommodated under the compound symmetry structure (exchangeable).   Steve Denham             ... View more

Hello again, I wanted to tell you that HPMIXED so far has worked brilliantly, and to thank you for your amazing help. Still having problems with GLIMMIX, but I figure I will try to bash my head against the proverbial wall with that for a while, before turning to the forums again. Again, I am greatly in debt to you! Kind regards, Daniel Johansson ... View more