[R-sig-eco] Continuous distribution for zero or positive values (in GLM or GLMM)

[Fred Takahashi]

Hello Antonio and Pavel

Thanks for the suggestions, but I think zero-inflated poisson and
negative binomial are not the best choices for my data. I have
measurements of mass (biomass of grasses) then my dependent variable
is continuous.

Fred

2011/5/18 Antonio Jesús Pérez Luque <ajpelu at gmail.com>:
> Hi Fred,
> For this models you can use the negative.binomial() function within the MASS
> package for the Negative Binomial model, and the zeroinfl () function of the
> pscl package for the Zero Inflated Poission models.
> Hope you find it useful.
> Antonio.
>
> On Wed, May 18, 2011 at 5:54 PM, Pavel Goldstein <dao4free at gmail.com> wrote:
>>
>> Hello Fred,
>> You can use Zerro Inflated Poisson or Negative binomial models.
>>
>> Pavel
>>
>> On Wed, May 18, 2011 at 6:46 PM, Fred Takahashi <fredtaka at gmail.com>
>> wrote:
>>
>> > Hello, just a basic question: what distribution I should use to
>> > analyze continuous data which can had zero or positive values (eg.
>> > mass of grasses in plots assuming that zero mass is meaningful)? My
>> > expected analysis is in the framework of GLM or GLMM (or
>> > alternatively, GAM / GAMM).
>> >
>> > One idea I had is to add 0.0001 to all values and use family=Gamma.
>> > That is a good approach?
>> >
>> > If a better choice is to use a different distribution, suggestions of
>> > packages to do that are welcome.
>> >
>> > Thanks,
>> > Fred Takahashi
>> > Universidade de Brasília - Brasil
>> >
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>
>
>
> --
> Antonio Jesús Pérez Luque
> Grupo de Ecología Terrestre.
> Departamento de Ecología.
> Centro Andaluz de Medio Ambiente, Universidad de Granada - Junta de
> Andalucía
> Avda. del Mediterráneo S/N. 18006. Granada. España
> Tel: +34 958241000 (ext. 31202)
> Fax: +34 958137246
> email: ajperez at ugr.es
> blog: http://ajperezluque.blogspot.com/
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