Difference-in-difference (DID) analysis in Stata

Dear Statalisters,

I have seen examples of DID analysis when the change takes place in a specific year, e.g. a tax cut in year 2001, then we can code post dummy=1 if year>2001.

I have a panel data set organized by firm industry and year. Some (not all) industries experience significant import tariff cuts in various years.

My question is: how do we code post dummy=1 in such cases?

e.g. industry A had a cut in 1999, industry B had a cut in 1997.


Thanks,

Rochelle