Re: multiple regression (ONKELINX, Thierry)

> Message: 1
> Date: Mon, 8 Feb 2010 11:02:37 +0100
> From: "ONKELINX, Thierry"<Thierry.ONKELINX@...>
> To: "Peter Solymos"<solymos@...>,	"Nathan Lemoine"
> 	<lemoine.nathan@...>
> Cc: r-sig-ecology@...
> Subject: Re: [R-sig-eco] multiple regression
> Message-ID:
> 	<2E9C414912813E4EB981326983E0A10406FDECE6@...>
> Content-Type: text/plain;	charset="iso-8859-1"
>
> Peter,
>
> I would think that the species richness is binomial distributed. Since there is a maximum number of
species that can be present. Therefore I would model it like
>
> glm(cbind(number.present, number.absent) ~ covariates, family = binomial)
>
>    

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).
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?

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

Alain

> HTH,
>
> Thierry
>
> ----------------------------------------------------------------------------
> ir. Thierry Onkelinx
> Instituut voor natuur- en bosonderzoek
> team Biometrie&  Kwaliteitszorg
> Gaverstraat 4
> 9500 Geraardsbergen
> Belgium
>
> Research Institute for Nature and Forest
> team Biometrics&  Quality Assurance
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> 9500 Geraardsbergen
> Belgium
>
> tel. + 32 54/436 185
> Thierry.Onkelinx@...
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>
> To call in the statistician after the experiment is done may be no more than asking him to perform a
post-mortem examination: he may be able to say what the experiment died of.
> ~ Sir Ronald Aylmer Fisher
>
> The plural of anecdote is not data.
> ~ Roger Brinner
>
> The combination of some data and an aching desire for an answer does not ensure that a reasonable answer can
be extracted from a given body of data.
> ~ John Tukey
>
>    

-- 

Dr. Alain F. Zuur
First author of:

1. Analysing Ecological Data (2007).
Zuur, AF, Ieno, EN and Smith, GM. Springer. 680 p.
URL: www.springer.com/0-387-45967-7

2. Mixed effects models and extensions in ecology with R. (2009).
Zuur, AF, Ieno, EN, Walker, N, Saveliev, AA, and Smith, GM. Springer.
http://www.springer.com/life+sci/ecology/book/978-0-387-87457-9

3. A Beginner's Guide to R (2009).
Zuur, AF, Ieno, EN, Meesters, EHWG. Springer
http://www.springer.com/statistics/computational/book/978-0-387-93836-3

Other books: http://www.highstat.com/books.htm

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