Dear all,

I want to compare the coefficients of the variable x from 2 different time periods and see if they are statistically different from each other. I use the code:

.reg emp x y z i.year if year>2003

.estimate store m1

.reg emp x y z i.year if year<2004

.estimate store m2

.suest m1 m2, cluster(region)

But Stata gives me an error saying that " year: factor variable base conflict". Is this because regressions are run on different time periods? is there a way to fix it and then test if coefficients of x are the same?

Could you suggest any alternative ways?