Message-ID: <DUB126-W76C71CD937F919A537C3ECD69A0@phx.gbl>
Date: 2014-10-31T20:49:26Z
From: Ludovico Frate
Subject: Binomial GLM: Is it the right way?
Dear List,
I'am trying to fit a GLM with a binomial error distribution but I am a little bit confused about the model.
I have 24 vegetation permanent plots, randomly distributed, sampled two times: 1962 and 2009. I am looking for any changes in vegetation composition and in particular based on plant traits (life forms).For each species, I assessed whether it had colonized (i.e. been in 1962 absent but in 2009 present) or become locally extinct (i.e. been in 1962 present but recently absent) in the plot.I would like to analyze whether a species trait affected the likelihood of colonizing or becoming extinct on a summit.
example: Colonizing species
Traits TOTAL COLONIZING PROB_COLChF 24 0 0ChC 24 1 0,041666667ChR 24 11 0,458333333ChSC 24 1 0,041666667ChS 24 18 0,75Ph 24 2 0,083333333Geo 24 18 0,75HeB 24 1 0,041666667HeC 24 36 1,5HeR 24 47 1,958333333HeS 24 161 6,708333333Th 24 28 1,166666667
Traits is the plant trait analyzed, TOTAL is the number of plots and COLONIZING represents the number of new species found in 2009 per plot, PROB_COL is the probability of colonization (COLONIZING/TOT)
However PROB_COL is >1, so I think that TOTAL should be different (i.e. total number of colonizing species)?
Any suggestions?Thank you,Ludovico
Ludovico
Frate
PhD student (University of Molise - Italy)
Environmetrics Lab
http://www.distat.unimol.it/STAT/environmetrica/organico/collaboratori/ludovico-frate-1
Department of Biosciences and Territory - DiBT
Universit? del Molise.
Contrada Fonte
Lappone,
86090 - Pesche (IS)
ITALIA.
Cel: ++39
3333767557
Fax: ++39 (0874) 404123
E-mail ludovico.frate at unimol.it
ludovicofrate at hotmail.it
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