Dear Saskia,

First of all, I think that your question would be better answered in other
list of discussion like ordnews@colostate.edu. Secondly, CCA does not
assume that your data are normal and homocedastic, the model assume an
unimodal and simetric response of species , but is robust to deviations of
this assumption. But I recomend to you ask this question at the list that I
suggested above.

Best Regards,

Gilson Carvalho


2013/4/5 SRuhl <saskia.ruehl@freenet.de>

> Hi everyone,
> I´m a student and relatively new to R so apologies in advance if this
> question seems stupid or obvious to you.
> I have collected a dataset with about 60 species of diatoms (count data
> from
> 19 different sample sites) and environmental variables for each site
> (salinity, pH, etc.). It´s all in the same dataset but distinct in R
> through
> the functions below
>
> diat <- diatom [, 1:60]  ##species
> envir<- diatom [, 61:66] ##environmental variables
>
> The long-term plan is to perform a canonical correspondence analysis (CCA
> in
> the vegan package) on it but the data obviously has to conform to some
> standarts first. Ideally, any two variables should be in a linear
> relationship and multivariate normality should be given as well as
> homoscedasticity (I haven´t tested for this one yet, that´ll be another
> adventure).  Now my data - surprise - does not conform to a normal
> distribution nor do the relationships seem linear so I need to transform it
> (but which parts?). The usual log transformation doesn't change anything so
> I found this one (the poisson generalized linear model)
> glm(formula, family=poisson(link=log), data=envir)
>
> again, it doesn´t work because I dont know what formula to put in.
> Any kind of help would be greatly appreciated, I am so lost...
> Thanks in advance,
> SRuhl
>
>
> On a side-note: the CCA runs on my data already but what good is that when
> the data is not in the right format? It may look completely different when
> the data fits all the requirements.
>
>
>
>
>
> --
> View this message in context:
> http://r.789695.n4.nabble.com/transforming-data-prior-to-CCA-tp4663454.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
> R-help@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>



-- 
Prof. Gilson Correia de Carvalho, M.Sc.
----------------------------------------------------
Pesquisador Associado
Laboratório de Ecologia Bentônica - LEB
Instituto de Biologia - UFBA
Universidade Federal da Bahia - UFBA
----------------------------------------------------
Professor Assistente
Departamento de Biointeração
Instituto de Ciências da Saúde - ICS
Universidade Federal da Bahia - UFBA
-----------------------------------------------------
Diretor Técnico
Holos Soluções Ambientais Ltda
-----------------------------------------------------
Skype: bio_gilson
GTalk: biogilson



-- 
Prof. Gilson Correia de Carvalho, M.Sc.
----------------------------------------------------
Pesquisador Associado
Laboratório de Ecologia Bentônica - LEB
Instituto de Biologia - UFBA
Universidade Federal da Bahia - UFBA
----------------------------------------------------
Professor Assistente
Departamento de Biointeração
Instituto de Ciências da Saúde - ICS
Universidade Federal da Bahia - UFBA
-----------------------------------------------------
Diretor Técnico
Holos Soluções Ambientais Ltda
-----------------------------------------------------
Skype: bio_gilson
GTalk: biogilson

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