[R] R wont accept my zero count values in the GLM with quasi_poisson dsitribution

[Michael Friendly]

On 7/28/2015 3:05 AM, Göran Broström wrote:
>
>
> On 28/07/15 08:33, Charlotte wrote:
>> Hello
>>
>> I have count values for abundance which follow a pattern of
>> over-dispersal with many zero values.  I have read a number of
>> documents which suggest that I don't use data transforming methods
>> but rather than I run the GLM with the quasi poisson distribution.
>> So I have written my script and R is telling me that Y should be more
>> than 0.
>
> No,  R  is telling you that you must have 0 <= y <= 1 (see below).
> For count data you should not use the binomial family, but rather
> 'poisson', or 'quasipoisson'.


With excess zeros, overdispersion is the symptom, but the quasipoisson
model is not the cure.
Even better than quasipoisson would be to use a ZIP (zero-inflated 
poisson) model or a hurdle model to explicitly model the
excess zeros.

These are handled by the countreg package, at present only
available on R-Forge.

  install.packages("countreg", repos="http://R-Forge.R-project.org")


>
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>