Hi, I am running a mixed model that has 4 groups with various blood levels and comparing each of the three groups to one control. For some reason when I include all the groups in one proc mixed model, with the control as my reference group, the solution for fixed effects yields equal standard errors for each group. However, when I run separate mixed models including only the control and one group, I get different standard errors. Is there any reason for this? This is the code I am using that includes all the groups, 0, 1, 2, 3,4 and 0 (control as reference). PROC MIXED data=data.data COVTEST NOITPRINT; CLASS ID; CLASS Group (ref="0"); MODEL level = Day Group/SOLUTION ddfm=bw; repeated /subject = ID; lsmeans Group / pdiff; run;quit; results look something like the below, is there any reason for the equal standard errors. This is the first time I encounter this....Is it better to run separate mixed models instead of one model with all the groups. Solution for Fixed Effects Effect Group Estimate Standard Error DF t Value Pr > |t| Intercept 3.4658 0.7105 8 4.88 0.0012 Day 0.2978 0.05967 47 4.99 <.0001 Group 2 -5.7163 0.8129 8 -4.45 0.0031 Group 3 -4.8571 0.8129 8 -4.73 0.0065 Group 4 -1.4241 0.8129 8 -0.53 0.7088 Group 1 0 . . .
... View more