David,
Ok, this clarifies much, thanks. Just one brief final remark on using
external instruments in -xtdpdsys- : Right after my last posting, while
I was doing a few more trials on the commands to understand their
syntax, by "accident" I once included -inst()- in xtdpdsys, and
interestingly it worked (no error message). [My initial question below
had been due to the fact that the stata manual doesn't point to -inst-
or any other option for including external instruments in -xtdpdsys-, so
I had assumed that -inst- was not an option]. Specifically, the results
for
xtdpdsys n w, inst(k)
and
xtdpd L(0/1).n w, div(k, nodiff) div(w) dgmmiv(n) lgmmiv(n)
are identical, which suggests that -inst- in -xtdpdsys- is in fact
serving properly to accommodate external instruments. So I guess the
stata manual may have just accidentally omitted this.
Thanks for all your help.
Tewodaj
