If you want to use PROC PLM to create an effect plot, you need to use the STORE statement in PROC MIXED: STORE MixStore;
Then use that name on the RESTORE= option in PROC PLM:
Proc plm restore=MixStore; effectplot slicefit(x=time sliceby=trauma); run;
However, the SLICEFIT statement expects the X= variable to be a continuous variable, but you have specified the TIME is a classification variable. Therefore the syntax you've written will generate an error.
You might want to read the article "Visualize a mixed model that has repeated measures or random coefficients."
I don't know what you are trying to accomplish, but here is some code that visualizes the model averaged over the subjects:
proc mixed data=long method=ml covtest;
class sub trauma;
model CAR = trauma time trauma*time;
repeated / SUBJECT=sub TYPE=CS;
store MixStore;
run;
quit;
Proc plm restore=MixStore;
effectplot slicefit(x=time sliceby=trauma);
run;
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