[R] hurdle model error why does need integer values for the dependent variable?

[Achim Zeileis]

On Fri, 18 Oct 2013, Lauria, Valentina wrote:

> Dear list,
>
> I am using the hurdle model for modelling the habitat of rare fish 
> species. However I do get an error message when I try to model my data:
>
>> test_new1<-hurdle(GALUMEL~ depth + sal + slope + vrm + lat:long + offset(log(haul_numb)), dist = "negbin", data = datafit_elasmo)
>
> Error in hurdle(GALUMEL ~ depth + sal + slope + vrm + lat:long + offset(log(haul_numb)),  :
>  invalid dependent variable, non-integer values
>
> When I do fit the same model with round(my dependent variable) the model 
> works. Sorry for the stupid question but could anyone explain me why? My 
> data are zero inflated (zeros occurring for 78%) and positively skewed.

hurdle() fits a count data distribution (poisson, negbin, geometric) by 
maximum likelihood. Hence, its response needs to be a count variable 
(i.e., integer). See vignette("countreg", package = "pscl") for the 
underlying likelihoods employed.

> Thank you very much in advance.
> Kind Regards,
> Valentina
>
>
>
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