Hi all,   I would like to expand on a topic that was discussed in this thread.   Here is the mixed-effects repeated measures model that I'm working with:   proc mixed data = analysis; class SubjectID Treatment Visit; model AVAL = Treatment Visit Treatment*Visit / s; repeated / subject = SubjectID type = AR(1); run;   There are 2 treatment groups and 4 visits (Baseline, Month 1, Month 3, and Month 6). My goal is to estimate the Percentage Change between Month 6 and Baseline for each treatment group. In this thread, PROC NLMIXED was suggested as a method to estimate for the Percentage Change. I followed the example from the thread to build the following model:   proc nlmixed data = analysis; parms b0=2 b1=0.5 b2=1.2 b3=1.2 b4=1.2 b5=1.2 b6=1.2 b7=1.2 sb=2 se=1; mu = b0 + b1*(Treatment="Active") + b2*(Visit="Month 1") + b3*(Visit="Month 3") + b4*(Visit="Month 6") + b5*(Treatment="Active")*(Visit="Month 1") + b6*(Treatment="Active")*(Visit="Month 3") + b7*(Treatment="Active")*(Visit="Month 6") + u; model AVAL ~ normal(mu, se); random u ~ normal(0, sb) subject=SubjectID; estimate 'Percentage Difference between Month 6 and Baseline for Active' ((b4 + b7)/(b0 + b1))*100; run;   My question is: How would I specify the AR(1) covariance structure as I did in PROC MIXED using PROC NLMIXED?   Any help or suggestions would be greatly appreciated!   Best, Diana ... View more