Dear colleagues,

I would appreciate if you may advise me on how to test for parallel trends in Stata for a DiD model with multiple groups and staggered treatment (i.e., policy reform). Almost all units become treated eventually. The original DiD model command is as follows
Code:
xtreg outcome i.policy i.year, fe vce(cluster id)
A very useful discussion on this is found in the links below, however I could not implement it in Stata.
http://econ.lse.ac.uk/staff/spischke/ec533/did.pdf
http://econ.lse.ac.uk/staff/spischke/ec524/evaluation3.pdf

Thank you in advance.