Hi, I am now using the PROC GENMOD to do the poisson regression to obtain the incidence rate of the outcome, I can get the incidence rate of the outcome in two exposure levels by using ILINK option in the LSMEANS. Then I want to get the incidence rate difference between two exposure levels by using the DIFF option in the LSMEANS, however, it does not provide the difference's estimate and its confidence intervals on the scale of the mean (the inverse linked scale). Does anyone help me? And what is the inverse linked scale of poisson? I am really confused about the transformation from -4.2980 into 0.01360. can anyone show me how to do the transformation? Thanks. Below is the code and the SAS output. proc genmod data=anadata. diet;
class hieng_c;
model chd = hieng_c / dist=poisson link=log offset=log_follow_time;
lsmeans hieng_c/diff=control means ilink cl plots=none;
run;
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