Hi,

This may be a weird question but I am trying to run a Difference in differences model in which I have two years of data and the treatment occurs in the second year. My post variable takes a value of 1 if the observation is from the second year and 0 otherwise. I was running my model and noticed something odd. Why is it that when I run the model: reg outcome DD post treat i.year i.month i.state i.year#i.month i.year#i.state and reg outcome DD post treat i.month i.state i.year#i.month i.year#i.state , I get different results? Does not the post variable account for year fe anyways?