I have a dataset with a continuous variable specifying the cumulative dose of a drug received at time t (drug received at multiple time points), a visit day variable, and a continuous outcome variable. I am fitting a model that cubic spline model with knots at the study days the drug is received to model the outcome variable with cumulative dose and a spline for visit day as predictors (and the interaction of day with dose) with subject specific intercept and slope. Below is the model code that I've used: proc glimmix data=dat; class subjectid; effect = spl(spline day/degree=3 knotmethod=list(5 10 15)); model outcome = spl | dose; random intercept day / subject=subjectid; run; I would like to estimate the contrast for a subject receiving a dose of 20 and a subject receiving a dose of 10 at day 12. I tried to write the following estimate statement: estimate "Dose 20 vs Dose 10 at Day 12" spl*dose [1, 12 20][-1, 12 10]; But the estimate is showing as "Non-est". Am I writing the contrast wrong?
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