Pardon this re-post! Gilbert McKenzie asks if the data is discrete or
continuous. They are continuous. The data on my mind at the moment
chemical analyses of geological samples. The variables are elements in
oxidized form. Some data sets have just 9 or so major constituents,
others include very large numbers of trace elements where the rarer may
present problems relating to the limits of detection.
Murray
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When analysing compositional data that sums across variables to a
constant it is well-known that Aitchison recommends analysing the log of
the ratios of the variables to their geometric mean. Others leave the
variables untransformed.
A third approach might be to analyse the logged proportions, ie the log
of the ratios of the variables to their arithmetic mean. Can anyone
point me to discussions in the literature about why this might be a good
or a bad thing to do?
Cheers, Murray
--
Dr Murray Jorgensen http://www.stats.waikato.ac.nz/Staff/maj.html
Department of Statistics, University of Waikato, Hamilton, New Zealand
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