Maarten,
Thank you for your suggestions. The dependent
variable in my model is the volume of sales/purchases
and the selection variable is the market participation
status: 0=net buyer, 1=autarkic, 2=net seller. As
dependent variables in the model I am using household
and farm characteristics.
I have been using the twostep estimation procedure and
experimented with different explanatory variables.
I got the oheckman command in the official help files,
FAQs, Examples, SJs, and STBs. A detailed description
of the command is available in The Stata Journal 2007,
7(2):1-16.
Once again, any advise/suggestions are greatly
appreciated.
Thank you for your time.
Regards,
Ana Rios
--- Maarten buis <[email protected]> wrote:
> --- "Ana R. Rios" <[email protected]> wrote:
> > I am trying to use oheckman but I am getting the
> > following message:
> > "Warning: Estimate of rho1 = . is outside feasible
> > interval [-1, 1]."
> > I would appreciate any suggestions/insights on how
> to
> > overcome this problem.
>
> It seems that -oheckman- has "converged" to an
> infeasible solution. The solution is to estimate a
> better model, as you haven't told us anything about
> your model I can't be very specific. One thing that
> jumps to mind with any heckman-like model is to make
> sure your model is properly identified, i.e. use
> instruments instead of relying on non-linearity.
> Another thing you might want to look at is to use
> the -twostep- option and see if that leads to any
> better estimates.
>
> -- Maarten
>
> BTW. -oheckman- is not in official Stata, so tell
> us where you got it.
>
> -----------------------------------------
> Maarten L. Buis
> Department of Social Research Methodology
> Vrije Universiteit Amsterdam
> Boelelaan 1081
> 1081 HV Amsterdam
> The Netherlands
>
> visiting address:
> Buitenveldertselaan 3 (Metropolitan), room Z434
>
> +31 20 5986715
>
> http://home.fsw.vu.nl/m.buis/
> -----------------------------------------
>
____________________________________________________________________________________
Never miss a thing. Make Yahoo your home page.
http://www.yahoo.com/r/hs
*
* 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/
