To detect smaller diVerences among closely related
groups in the pilot study, samples were subjected to the
supervised learning method PLS (Partial Least Square),
also available in the Sirius 7.0 package. New variables were
subsequently added to the data matrix, one for each sample
group. The variable belonging to a group was given the
value +1 for the samples belonging to that particular group
and ¡1 for all the other samples (i.e. these are dependent