Compare changes within groups in a panel dataset

[Ronald Biefinger]

Hello everyone,

probably an easy one for you: I use a panel data set (several groups and years per group) and want to check whether a certain status within a group changed from the first year to the last year observed. The sample period is not always the same for all groups. The characteristic I want to compare is the legal status of a company, i.e. the variable "status" would contain values such as "Ltd", "Public" etc. If the status remained the same a new variable created should take on the value 1 and 0 otherwise. Finally I would like to compare the change, i.e. how many companies (groups) have changed their legal status (e.g. 200 out of 1000 companies changed their status -> the result should yield 0.2).

Could you help me out with the code please? Thank you!

[Alexis Penot]

For the first request, I would try
bysort group year: generate status_change = (status==status[_n-1])

[Nick Cox]

This is an FAQ: http://www.stata.com/support/faqs/da...ions-in-group/

[Ronald Biefinger]

Thank you very much for the quick and helpful comments.

[Nick Cox]

To count companies rather than observations, use egen, tag() to tag each company just once.

[Carlo Lazzaro]

Ronald may also be interested in taking a look at -xttrans- under -help xttab- and related entry in Stata 13.1 .pdf manual.