[R-sig-eco] hurdle model

[Yingjie Zhang]

Hi,

There is a reason why am I addict to Quasi likelihood, since Hurdle  from 'pscl' use Zero Truncated Poisson regression for the non-zero part, which incapable of handling the over-disperson comes from the positive part of the data. Apparently, Quasi likelihood is at least a better choice. I've noticed the hurdle they used for the paper comes from package 'stats' instead of 'pscl', I didn't find this version of hurdle in r...

On 19 Aug 2010, at 10:55, Gavin Simpson wrote:

> On Thu, 2010-08-19 at 10:30 +0200, Yingjie Zhang wrote:
>> I'd like to try the same way to my dataset, hurdle but estimated by
>> 'quasi-likelihood', but it's not in the standard 'pscl' package I
>> think, right?
> 
> Please keep discussion on list; just because I replied doesn't give you
> a direct line to my inbox...
> 
> Why would you want a quasi-likelihood when you could have the real
> thing? Seriously, if there is no likelihood you can't do likelihood
> ratio tests, compare models using AIC/BIC etc.
> 
> Just use hurdle() if it fits the form of model you are after. don't
> worry about likelihoods, quasi or otherwise. Check you are happy with
> the range of models you could fit with hurdle() and use it. If you
> aren't happy then you'd need to look elsewhere, but don't get hung up on
> the quasi-likelihood bit.
> 
> My Tuppence,
> 
> G
> 
>> 
>> 
>> On 19 Aug 2010, at 10:17, Gavin Simpson wrote:
>> 
>>> On Thu, 2010-08-19 at 09:52 +0200, Yingjie Zhang wrote:
>>>> Hello everyone,
>>>> 
>>>> Does anyone of you using hurdle model? I am reading a paper which said
>>>> " Hurdle model removes effect of zero-inflation and over-dispersion in
>>>> the non-zero observations using a quasi-likelihood", I've checked the
>>>> help file from hurdle in R, which said differently that"for non-zero
>>>> obs normally a truncated poisson/NB is used" ... just want to make
>>>> sure, does it really estimated the parameter by "quasi-likelihood"
>>>> 
>>>> Thanks,
>>>> Yingjie Zhang
>>>> Biostatistician
>>> 
>>> The authors of that paper might have fitted their hurdle model using a
>>> quasi likelihood but that is not, AFAICT, what is used in the hurdle()
>>> function in package 'pscl', which maximises a proper log likelihood.
>>> 
>>> But hard to say from what you have provided.
>>> 
>>> G
>>> -- 
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>>> Dr. Gavin Simpson             [t] +44 (0)20 7679 0522
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>>> 
>> 
> 
> -- 
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> Dr. Gavin Simpson             [t] +44 (0)20 7679 0522
> ECRC, UCL Geography,          [f] +44 (0)20 7679 0565
> Pearson Building,             [e] gavin.simpsonATNOSPAMucl.ac.uk
> Gower Street, London          [w] http://www.ucl.ac.uk/~ucfagls/
> UK. WC1E 6BT.                 [w] http://www.freshwaters.org.uk
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>