Hi there - The following code works but only with a very small sample size.  My dataset is big and I get an ERROR message when I submit the code using the entire dataset.  I have never used GLIMMIX, I'm not familiar with it.  I wonder if this model can be run using MIXED instead?  Would that help? Or are there any other ways to run this code more efficiently?   proc glimmix data=xx; class studyid;  effect spl = spline(quarter / details naturalcubic basis=tpf(noint)knotmethod=percentiles(5));    model avgdose = spl /s ddfm=kr;    random int spl /subject = studyid type=vc solution;  /*try vc instead of un*/         ods output parameterestimates=sf(keep=effect estimate                                   rename=(estimate=overall));       ods output solutionr=sr(keep=effect subject estimate                                  rename=(estimate=ssdev)); run;   Here is the error I get: ERROR: Model is too large to be fit by PROC GLIMMIX in a        reasonable amount of time on this system. Consider        changing your model. ... View more