Dear Stata-listers,
Although I have read some materials on the treatment
effect model, I am still not sure whether I should
specify a structural or a reduced-form equation for
the treatment(selection) equation. According to the
textbooks of Wooldridge (2002) and Greene (2003), it
seems that a reduced-form treatment equation should be
used. Though in Maddala (1983, p120-122), it is not
clear which form is specified for the probit equation.
{It seems that the example given in the on-line help [
the command in (1)]specifies the excluded variables
only, which would not produce a reduced-form results
for the treatment equation [as the command in (2)
does].
(1)treatreg ww wa cit, treat(wc=wmed wfed) twostep
(2)treatreg ww wa cit, treat(wc=wa cit wmed wfed)
twostep
As a result, I am puzzled at the correct way to
specify the variables (indepvars_t) for the treatment
equation. The results will be different depending on
whether only excluded variables or all the exogenous
variables are specified in the treatreg command.
[Unlike ivreg command which would produce the same
results when we specified either way. ]
Would be grateful that someone can give me some
guidance on this issue.
Thanks you for your kind help in advance.
Richard Lo
___________________________________________________________
All New Yahoo! Mail � Tired of unwanted email come-ons? Let our SpamGuard protect you. http://uk.docs.yahoo.com/nowyoucan.html
*
* For searches and help try:
* http://www.stata.com/support/faqs/res/findit.html
* http://www.stata.com/support/statalist/faq
* http://www.ats.ucla.edu/stat/stata/
