Hello,   I am running into an issue with my mixed model, where the addition of the SOLUTION option in the random statement of PROC MIXED drastically affects the fixed effects estimates. Below is the model:   proc mixed data=eff method=REML; by trtgrpn trtgrp; class TRTPN (ref=first) USUBJID STRATAR; model AVAL = TRTPN BASE avisitn TIMEK avisitn*TRTPN TIMEK*TRTPN STRATAR / solution ddfm=kr alpha=0.05 cl; random INT avisitn TIMEK / sub=USUBJID type=un v; estimate "Acute Slope, No Response" avisitn 52 avisitn*TRTPN 0 52 / e cl; estimate "Acute Slope, Response" avisitn 52 avisitn*TRTPN 52 0/ e cl; estimate "Chronic Slope, No Response" avisitn 52 TIMEK 52 avisitn*TRTPN 0 52 TIMEK*TRTPN 0 52 / e cl; estimate "Chronic Slope, Response" avisitn 52 TIMEK 52 avisitn*TRTPN 52 0 TIMEK*TRTPN 52 0 / e cl; estimate "Difference, Chronic Slope" avisitn*TRTPN 52 -52 TIMEK*TRTPN 52 -52 / e cl; run;   In the above model, TRTPN reflects No response vs response, STRATAR reflects a 4 level stratification variable, AVISITN reflects the categorical visit (Week 6 to Week 108), BASE is the baseline value, and TIMEK is the time from change point (Week 6). TRTGRP/TRTGRPN reflects a subgroup of 2 different treatments. The results from this model are as follows: If I include the S option in the RANDOM statement, the estimates/DF for TRTGRPN = 2 drastically change: Any thoughts on why this might be occurring? ... View more