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RE: st: AW: double hurdle model with Tobit second stage estimation


From   "Erickson, Ken" <ERICKSON@ers.usda.gov>
To   <statalist@hsphsun2.harvard.edu>
Subject   RE: st: AW: double hurdle model with Tobit second stage estimation
Date   Wed, 25 Feb 2009 13:59:29 -0500

Hi David and 'Statalisters',

My colleague Mike just suggested this:

...Ken,

Can you send my response to him?

You need to use a drop statement   drop if <var> == 0

Do this before the second stage...

See "From the help desk: hurdle models," The Stata Journal, 2003, 3, Number 2, pp.178-184.

Hope this helps!
Ken Erickson

-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of David Jacobs
Sent: Wednesday, February 25, 2009 1:47 PM
To: statalist@hsphsun2.harvard.edu
Subject: Re: st: AW: double hurdle model with Tobit second stage estimation

You've probably thought of this as well, but what 
about the -zip- or -znb- models in Stata.  Those 
options allow large proportions of zeros in your outcome variable.

Is the problem with these models that the values 
above zero are not integers?  If they are 
integers or could be made into integers without 
messing things up, then these two equation count estimators might work.

Dave Jacobs

At 01:16 PM 2/25/2009, you wrote:
>Heckprob is not appropriate in my case. Heckprob 
>would treat the pile of zeros i have as 
>unobserved whereas the Tobit treats them as 
>observed zeros. This is the case in my data and 
>therefore heckprob is not an appropriate model. 
>I could run a first stage Probit then a second 
>stage Tobit. However, the Tobit in the second 
>stage does not use all the data observed and 
>hence the standard errors will not be correct 
>leading to wrong t statistics and be unable to interpret the results.
>
>Kirimi
>
>Martin Weiss wrote:
>><>
>>Have you looked into
>>
>>
>>*************
>>help heckprob
>>*************
>>
>>?
>>
>>
>>HTH
>>Martin
>>
>>
>>-----Ursprüngliche Nachricht-----
>>Von: owner-statalist@hsphsun2.harvard.edu
>>[mailto:owner-statalist@hsphsun2.harvard.edu] Im Auftrag von Kirimi Sindi
>>Gesendet: Mittwoch, 25. Februar 2009 17:43
>>An: statalist@hsphsun2.harvard.edu
>>Betreff: st: double hurdle model with Tobit second stage estimation
>>
>>Hey,
>>
>>I working on a double hurdle model. The first 
>>stage is a Probit model and the second stage is 
>>Tobit due to pile up of zeros. Is there a do 
>>program that can assist me in this procedure to 
>>get the correct standard errors accounting for the first stage estimation?
>>
>>Thank you,
>>
>>Kirimi
>>
>>
>
>--
>*******************************
>Imagination is more important than knowledge. 
>For while knowledge defines all we currently 
>know and understand, imagination points to all 
>we might yet discover and create.
>*******************************
>
>Kirimi Sindi
>PhD Candidate
>Department of Agricultural,
>Food, and Resource Economics
>Room 20 Cook Hall
>Michigan State University
>East Lansing,  MI  48824
>Telephone: +1-517-353-5320
>Home Tel : +1-517-355-8151
>Fax: +1-517-432-1800
>
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