Changing base category in xtdidregress command

[Federico Stravo]

Hi everyone. I am using the command xtdidregress to estimate a diff-in-diff regression on Stata. It looks like this:

xtdidregress (score) (treat_variable), group(firm) time(year) aequations allbaselevels

My time variable, year, goes from 2008 to 2017. I am using fixed effects for year in my regression. When I use the command xtdidregress, it takes the first year, 2008, as the base (omitted) category in my regression. However, I would like Stata to take 2013 as my base category. Is there a way I can do that? Typing help xtdidregress did not help me much.

Thank you!

[Enrique Pinzon (StataCorp)]

Hi Federico,

You could use the -nogteffects- option. This option tells the command to not include time fixed effects by default in this case. You would then have to include the time dummies on the first parenthesis. In your case it would look something like:

 xtdidregress (score ib2013.year) (treat_variable ), group(firm) time(year) aequations allbaselevels nogteffects

[Federico Stravo]

It worked, thank you so much Enrique!