# Re: st: Re: Question Tobit model

 From Johannes Geyer To statalist@hsphsun2.harvard.edu Subject Re: st: Re: Question Tobit model Date Mon, 21 Apr 2008 10:35:56 +0200

```- Another question I had was about the McDonald-Moffit Decomposition,
which demonstrated that for this model the total marginal effect have
three parts related with the probability of the dependent variable
being uncensored or not

this is a stata faq:
http://www.stata.com/support/faqs/stat/mfx_ologit.html

I copied the relevant lines:

___________________
intreg and tobit
The marginal effects for the probability of being uncensored are
(1) mfx compute, predict(p(a,b))
where a is the lower limit for left censoring and b is the upper limit for
right censoring.
The marginal effects for the expected value of the dependent variable
conditional on being uncensored, E(y | a<y<b), are
(2) mfx compute, predict(e(a,b))
where a is the lower limit for left censoring and b is the upper limit for
right censoring.
The marginal effects for the unconditional expected value of the dependent
variable, E(y*), where y* = max(a, min(y,b)), are
(3) mfx compute, predict(ys(a, b))
where a is the lower limit for left censoring and b is the upper limit for
right censoring.
_____________________

McDonald and Moffit showed that a change in the independent variable x has
two effects: it affects the conditional mean of y in the positive part of
the distribution (2), and it affects the probability that the observation
will fall in that part of the distribution (1). The sum of both effects
gives the unconditional effect (3). (Greene 2003, Econometric analysis,
p.766)

Johannes

owner-statalist@hsphsun2.harvard.edu schrieb am 21/04/2008 10:08:20:

> First of all have a look at:
> http://www.stata.com/support/faqs/res/statalist.html#private
>
> -intreg- is more general than -tobit-
>
> -findit McDonald-Moffit- doesn't show up any results, so I don't know.
>
> Maarten
>
> --- Marco <panser2@hotmail.com> wrote:
> > Thanks for your help about the commands for two-limit tobit model.
> > However I have two questions questions.
> >  - I received  two different answers that suggested the use of:
> > -intreg- or -tobit- . Do you know which is the difference?.
> >
> > - Another question I had was about the McDonald-Moffit Decomposition,
> >
> > which demonstrated that for this model the total marginal effect have
> >
> > three parts related with the probability of the dependent variable
> > being uncensored or not. However I cannot find the commands for
> > calculating these decompositions. Do you know them?
> >
> > Thanks,
> > Marco
> >
> > _________________________________________________________________
> > Invite your mail contacts to join your friends list with Windows Live
> > Spaces. It's easy!
> >
> http://spaces.live.com/spacesapi.aspx?
> wx_action=create&wx_url=/friends.aspx&mkt=en-us
>
>
> -----------------------------------------
> Maarten L. Buis
> Department of Social Research Methodology
> Vrije Universiteit Amsterdam
> Boelelaan 1081
> 1081 HV Amsterdam
> The Netherlands
>
> Buitenveldertselaan 3 (Metropolitan), room Z434
>
> +31 20 5986715
>
> http://home.fsw.vu.nl/m.buis/
> -----------------------------------------
>
>
>       __________________________________________________________
> Sent from Yahoo! Mail.
> A Smarter Email 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/

*
*   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/
```