how to create a variable for the previous year for the same firm

[Yun Cheng]

Hello!

I have some data that could use firm id and year to identify which firm it is, and which year the observation occurs. For each firm id, I want to create an observation for its previous year, e.g., with firm id 2345 in year 2009, I want another line also with firm id 2345, but the year shown is 2008. How can I do this?

Thanks a lot for any help : )

[Mike Lacy]

Presuming there is only one observation per firm/year, this sounds like:

expand 2, gen(new)
replace year = year-1 if new

[Yun Cheng]

Thanks Mike, this works well.