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

[Remington, Richard]

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."

best,
Richard

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

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 help.search("two-part") and many other similar guesses.
>>
>>Thanks,
>>Richard
>>
>>-- 
>>Richard Chandler, M.S. Candidate
>>Department of Natural Resources Conservation
>>UMass Amherst
>>(413)545-1237
>>
>>______________________________________________
>>R-help at stat.math.ethz.ch mailing list
>>https://stat.ethz.ch/mailman/listinfo/r-help
>>PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
> 
>