Re: [R] function for "two-part" or "two-condition" models

From: Remington, Richard <>
Date: Wed 29 Jun 2005 - 03:15:11 EST

Two alternatives to the zero inflated Poisson (ZIP) model are mentioned in Jung, Jhun, and Lee (Biometrics, vol 61, no 2, June 2005, p626):

"Although the ZIP model is more general than the standard Poisson, count data with many zeros are often more dispersed than the ZIP model. In this case, the use of a zero-inflated negative binomial (ZINB) distribution or a zero-inflated generalized Poisson distribution is a good alternative."


Richard E. Remington
KERN Statistical Services, Inc.
PO Box 1046
Boise, ID 83701
Tel: 208.426.0113

Andrew Robinson wrote:

> Hi Richard,
> I'm not sure that I can imagine how data can have too many zeros to be
> fit well with zero-inflated Poisson models. Won't the excess zeros be
> accommodated by increasing the the inflation?
> In any case, if you want a model that separates the zeros from the
> occurrences before fitting a Poisson model to account for variation in
> abundance then it might be safest to do that split manually.
> Another angle to try is to treat it as a special case of a finite
> mixture regression. I think that some of Jim Lindsey's code will fit
> such models. Google can help you find his wbsite.
> An MS student of mine explored these models for regeneration modeling.
> I'd be happy to send you a pdf of his thesis if it would help.
> Cheers,
> Andrew
> On Mon, Jun 27, 2005 at 03:35:30PM -0400, Richard Chandler wrote:
>>Hello, >> >>This is an (hopefully) improved question of one I posted several weeks >>ago. Does anyone know of a function for fitting "two-part" models? >>These models are designed to handle count data with so many zeroes >>that they can't be fit well with zero-inflated Poisson models or other >>'typical' GLMs. My understanding is that they work by first fitting a >>binomial model to separate the zeros from the occurrences (positive >>integers) before fitting a Poisson model to account for variation in >>abundance. >> >>I have tried"two-part") and many other similar guesses. >> >>Thanks, >>Richard >> >>-- >>Richard Chandler, M.S. Candidate >>Department of Natural Resources Conservation >>UMass Amherst >>(413)545-1237 >> >>______________________________________________ >> mailing list >> >>PLEASE do read the posting guide!
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Received on Wed Jun 29 03:19:18 2005

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