Hello, I am working with a polynomial regression model using generalized estimating equations in GENMOD. My goal in using the estimate statement is to compare treatment groups at various time point. I am having problems getting the estimate statement to work with my reference treatment group at particular time points and I am not sure why. The time points that I am using are 60, 90, 120, 150, 180, 210, 240, and 270. The time variables are centered using a mean value of 165. time1 is the centered value of time, time2 is this value squared, and time3 is this value cubed. I have 5 treatment groups and am trying to estimate the difference between two groups, one of which is the reference group in the model. I tried to code the reference group as I did all other groups, but this did not work, so I set the reference group to zero. The estimate statement produces the expected result for the first estimate statement but indicates that the second estimate statement is non-estimable. Any insight would be greatly appreciated. proc genmod data = diblong1; class treatment mouse_ID; model lngluc = treatment time1 time2 time3 treatment*time1 treatment*time2 treatment*time3/type3; repeated subject=mouse_ID / corr=EXCH corrw; estimate 'Diff tx1 vs. tx5 at time = 60' treatment 1 0 0 0 0 treatment*time1 -105 0 0 0 0 treatment*time2 11025 0 0 0 0 treatment*time3 -1157625 0 0 0 0; estimate 'Diff tx1 vs. tx5 at time = 150' treatment 1 0 0 0 0 treatment*time1 -15 0 0 0 0 treatment*time2 225 0 0 0 0 treatment*time3 -3375 0 0 0 0; run; Thanks! Susan
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