[R-sig-eco] multiple regression (ONKELINX, Thierry)

ONKELINX, Thierry Thierry.ONKELINX at inbo.be
Mon Feb 8 17:05:07 CET 2010

Dear Alain,

Thank you for your comments.

> Interesting thought. Maybe correct. But there are a few 
> things to think
> about:
> 1. You have to assume that sampling was such that all species 
> out there have ended up in the data. Formulated 
> differently...you need to know the N_i (maximum number of 
> possible species) in the B(p_i,N_i).

I assume that one knowns all species that could occur in the region.
That is not the same as all samples species. 

> 2. Not sure how the variance structure would work out; 
> Poisson or NB versus Binomial. I guess it may work out ok.
> 3.  B(p_i,N_i) means N_i independent (!) trials, each (!) 
> with probability p_i of success. But what happens if these 
> trials (=species) are not independent?

Agreed that this might be problematic. But isn't this also a problem
with a Poisson model? Since you assume that the number of species only
depends on the covariantes and not on the presence of some species?

> Anyway....it is not my problem....but you would need to think 
> about these things.

I was replying to a question. So it is is my problem neither ;-) Or are
least not at present, as I might get similar datasets in the future.

> Alain

Best regards,


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