Hello,
  I use microarrays to create and test a classifier and I have a question
realeted to this topic. Theoreticaly one cannot use a test set in creating a
classifier. It is obvious when thinking about selection of differentiatially
expressed genes and about training. But what about such steps like
normalization, non-specific gene selection (for example selection of genes
with high variance) and standardization? Can I perform this steps on the
whole dataset? Or should I do it only using the training set? I saw that
people rather don't care and use the whole dataset to perform this steps but
I'm not sure if this is really correct.

Best regards,
Theresa Brandt

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