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Re: st: Zero-inflated Negative Binomial models for Panel data


From   Stas Kolenikov <skolenik@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Zero-inflated Negative Binomial models for Panel data
Date   Thu, 11 Mar 2010 09:25:33 -0600

On Wed, Mar 10, 2010 at 10:48 PM, Jabr, Wael M <
wael.jabr@student.utdallas.edu> wrote:

> Does Stata support Zero-inflated Negative Binomial models for Panel data?
> I have researched some of the documentations but couldn't find a reference
> to that.
>

Does such a model exist at all in the literature?

Zero-inflation is a two part (mixture) model. I don't think it has a
sufficient statistic, so you cannot do any sort of fixed effects. Where
exactly do you want to place the random effects? You can say that you have a
random effect in the mixture equation only (inflation for zeroes); you can
say that you have a random effect in the main equation (binomial
probabilities) but not in the mixing equation; you can have random effects
in both (allowing them to correlate, I guess); or you can have a single
random effect that affects both equations with certain loadings (although
such model may be difficult to identify). Those would be four different
kinds of models that will have different fit to data.

-gllamm- does not support the negative binomial family. However since the
negative binomial model is the Poission model with a gamma random effect
(integrated over), you may be able to get some leverage out of Poisson
family.

-- 
Stas Kolenikov, also found at http://stas.kolenikov.name
Small print: I use this email account for mailing lists only.
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