Hi all,

I'm trying to recreate the results obtained by ter Braak (1985) for the
hspider dataset contained in the VGAM package, using the cca() function
from the vegan package. For that, I use the following code :

library(VGAM)
library(vegan)
data(hspider)

hs.spec <- sqrt(hspider[,7:18])
hs.ev <- as.data.frame(scale(hspider[,1:6])) # assuming the data is already
log-transformed

Model<-cca(hs.spec~.,data=hs.ev)
summary(Model)

ter Braak mentions in table 2 of his paper the "canonical coefficients" and
"correlation coefficients" of the first two axes (see
http://www.jstor.org/stable/10.2307/1938672 ). However, when I try to
extract them as follows :

coef(Model)
intersetcor(Model)

I get results that differ from the table given by ter Braak. I can explain
the differences in sign (that's normal, as the solution of cca is defined
up to the sign), and I can believe there would be small differences as
we're talking different ways of estimation, but the canonical coefficients
for the second axis differ substantially.

My question :

- Did I use the correct methods to extract what ter Braak calls "canonical
coefficients" and "correlation coefficients"?
- is there a logical explanation for the big difference in some results ?


-- 
Joris Meys
Statistical consultant

Ghent University?
Faculty of Bioscience Engineering
Department of Mathematical Modelling, Statistics and Bio-Informatics

tel : +32 9 264 59 87
Joris.Meys@Ugent.be
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