Again the first step is to append the data sets:

use panel2007
gen year=2007
save panel2007_append
use panel2008
gen year=2008
append using panel2007_append

You can observe that there is a person who only appears once with duplicates report:

duplicates report id

If you want to figure out who it is and examine their data, you can follow the procedure for identifying duplicates. Just keep in mind that in this case everyone should have two copies, and anything else is a problem:

bysort id: gen copies=_N
l if copies==1

Last Revised: 8/22/2011