proc genmod data=sas_stata;
class age_group_var id CPSUM CSTRATM;
model DIETNUTR = age_group_var/ dist = poisson link = log;
weight PATWT;
x = CPSUM(CSTRATM)
repeated subject = id * x/ type = unstr;
estimate 'Beta' age_group_var 1 -1/ exp;
run;