[R] Zinb for Non-interger data

Vito Muggeo (UniPa) vito.muggeo at unipa.it
Tue Jul 21 10:52:08 CEST 2009


I think that the (impressive) gamlss package (see 
http://www.gamlss.com) may be helpful.

If I remember correctly, in gamlss you can fit model with zero-inflated 
continuous distributions

hope this helps you,
vito


Alain Zuur ha scritto:
> 
> JPS2009 wrote:
>> Sorry bit of a Newbie question, and I promise I have searched the forum
>> already, but I'm getting a bit desperate!
>>
>> I have over-dispersed, zero inflated data, with variance greater than the
>> mean, suggesting Zero-Inflated Negative Binomial - which I attempted in R
>> with the pscl package suggested on
>> http://www.ats.ucla.edu/stat/R/dae/zinbreg.htm
>>
>> However my data is non-integer with some pesky decimals (i.e. 33.12) and
>> zinb / pscl doesn't like that - not surprising as zinb is for count data,
>> normally whole integers etc.
>>
>> Does anyone know of a different zinb package that will allow non-integers
>> or and equivalent test/ model to zinb for non-integer data? Or should I
>> try something else like a quasi-Poisson GLM?
>>
>>
>> Apologies for the Newbie question! Any help much appreciated!
>> Thanks!
>>
> 
> Is it really non-integer...or is it a density (in which case you could use
> NB + offset)?
> 
> 
> The quasi-Poisson will not help you with the zero inflation.
> I'm afraid you will have to do some hard programming by combining the 0-1
> binomial part with a continuous distribution on the second part of the
> data......and I guess the easiest is to do this in MCMC. Perhaps the Gamma
> distribution can be used? You would have to adjust all likelihood equations
> as Gamma doesn't allow for zeros. But perhaps another continuous
> distribution is more appropriate...depends on your data.
> 
> 
> Alain Zuur
> 
> 

-- 
====================================
Vito M.R. Muggeo
Dip.to Sc Statist e Matem `Vianelli'
Università di Palermo
viale delle Scienze, edificio 13
90128 Palermo - ITALY
tel: 091 6626240
fax: 091 485726/485612
http://dssm.unipa.it/vmuggeo




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