Hello All, I got this panel data with individual purchase, advertising
and promotion to individuals.

I can setup regular regression as purchase=intercept+ad+promotion. I
want to test fixed effect by adjusting intercept to change across
individual.. But I am not sure how to do this when the purchase is
distributed in Poisson.

Thanks for any suggestion. I did the normal poisson regression with
nlmixed procedure, so if you can help me to integrate the fixed effect
into nlmixed procedure, that would be very nice.