Message: 1
Date: Mon, 8 Feb 2010 11:02:37 +0100
From: "ONKELINX, Thierry"<thierry.onkel...@inbo.be>
To: "Peter Solymos"<soly...@ualberta.ca>, "Nathan Lemoine"
<lemoine.nat...@gmail.com>
Cc: r-sig-ecology@r-project.org
Subject: Re: [R-sig-eco] multiple regression
Message-ID:
<2e9c414912813e4eb981326983e0a10406fde...@inboexch.inbo.be>
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
Gaverstraat 4
9500 Geraardsbergen
Belgium
tel. + 32 54/436 185
thierry.onkel...@inbo.be
www.inbo.be
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
Statistical consultancy, courses, data analysis and software
Highland Statistics Ltd.
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UK - AB41 6FN Newburgh
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