I am trying to run an adjusted poisson regression in SAS using our existing data.
The model is: # of cases of disease= years + screening of disease rate. I am using an offset = log(total population).
My issues lie in the fact that when using YEAR as my primary independent variable and adjusting for another variable (screening rate), there are not enough degrees of freedom. I have 7 years (observation level) of data, so when I try to adjust for the screening rates the screening rate variable has no estimate value.
any thoughts on how to get by this or another way to structure this to be able to do this analysis?