Re: st: Two part model - How to combine models?

["E. Paul Wileyto" <epw@mail.med.upenn.edu>]

Look up Stata help on zip, zinb, ztp, ztnb.  I thought there was also a 
zero-inflated binomial, but I can find no reference to it.

P

Tamara Pejovic wrote:

> Hi,
> I have a quick question. I have a response variables that is 
> positively skewed and contain a substantial proportion of zeroes. 
> Since a common method for analyzing this type of data is a two-part 
> model I have the analysis of three stages:
> The first involved creating two sets of data from the original: one 
> showing whether or not the problem is present and the other indicating 
> the "level of the problem" when problem is present.
> The second stage involved modelling occurrence of problem, using 
> logistic regression, and separately modeling the level data using 
> ordinary regression.
>
> Finally, the third stage should be combining the two models in order 
> to estimate the expected "level of the problem" for a specific set of 
> values of possible predictors.
>
> My question is how to do this? Is it just enough to multiple 
> probabilities using conditional probabilities rule? Does STATA have a 
> module for solving two-part models?
>
> Thanks,
> Tash
>
>
> *
> *   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/
--
E. Paul Wileyto, Ph.D.
Assistant Professor of Biostatistics
Tobacco Use Research Center
School of Medicine, U. of Pennsylvania
3535 Market Street, Suite 4100
Philadelphia, PA  19104-3309

215-746-7147
Fax: 215-746-7140
epw@mail.med.upenn.edu
http://mail.med.upenn.edu/~epw/ 
*
*   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/