[R] GAM hurdle models

[Achim Zeileis]

On Thu, 5 Jun 2008, John Poulsen wrote:

> Hello,
>
> I have been using mgcv to run GAM hurdle models, analyzing presence/absence 
> data with GAM logistic regressions, and then analyzing the data conditional 
> on presence (e.g. without samples with no zeros) with GAMs with a negative 
> binomial distribution.
>
> It occurs to me that using the negative binomial distribution on data with no 
> zeros is not right, as the negative binomial allows zeros.
>
> Does anyone know of a package that does negative binomial GAM hurdle models? 
> Or is there another quick fix to overcome this problem (e.g. using 
> quasipoisson)?

Packages "VGAM" and "gamlss" both contain functionality for fitted 
zero-inflated GAMs. If I recall correctly, both have ZIP and at least VGAM 
also has ZINB as well as hurdle models for both distributions (under the 
name "zero-altered" models).

I think that both require to use the same set of regressors in both parts 
of the model. An implementation of zero-inflated models and hurdle models 
without GAM effects but with separate sets of regressors is available in 
"pscl".

Further information about the packages is available from:
   http://www.stat.auckland.ac.nz/~yee/VGAM/
   http://www.jstatsoft.org/v23/i07/
   vignette("countreg", package = "pscl")

hth,
Z

> Thanks for your suggestions,
> John
>
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