Multivariate analyses

Guido Flamini flamini at FARM.UNIPI.IT
Fri Jul 13 09:50:58 CDT 2001


Dear Taxacomers,

I have a problem with the multivariate statistical analyses of my data. I
want to perform a PCA and a Cluster Analysis on chemical data (composition
of the essential oils from different collecting places).
Unfortunately each sample contain values ranging   between 0.01% to 96%.
So, when I perform the calculations, nearly all the variance is explained
by the first axis and I am not able to obtain the dispersion of the data on
the other axis. I have tried to convert my data using the arcsin function,
but the graphs are still ugly.
Can you give me some suggestions?
Is it correct to discard the 90% values from all the samples and reconduct
to 100% the other percentages and then perform the analysis with these new
data? (moreover, in this way I obtain the interpretation that I like!!).

Thank you in advance,

Guido


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Dr. Guido Flamini
Dipartimento di Chimica Bioorganica e Biofarmacia
Via Bonanno 33, 56126 Pisa, Italia
Tel: +3905044074; Fax: +3905043321
e-mail: flamini at farm.unipi.it
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