Dear Saskia, First of all, I think that your question would be better answered in other list of discussion like ordn...@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.ru...@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 [[alternative HTML version deleted]]
______________________________________________ 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.
