Dear Colleagues,

Greetings from Switzerland !
I agree with the statements of Wolfgang and Adai. Using all chips will 
certainly put you on the safe side. 
I wonder what you feel would be the minimal number of chips for a "stable" 
(meaning that a larger set would give essentially the same results) RMA 
processing? People from GeneLogic told me that about 20 chips are 
sufficient.
Is it possible to run RMA using Bioconductor with 200 chips and get the 
results back within a reasonable time?

Best regards,
Martin






Adaikalavan Ramasamy <ramasamy@cancer.org.uk>
Sent by: bioconductor-bounces@stat.math.ethz.ch
15.02.2006 01:01
Please respond to ramasamy

 
        To:     Wolfgang Huber <huber@ebi.ac.uk>
        cc:     Sylvia.Merk@ukmuenster.de, bioconductor@stat.math.ethz.ch, (bcc: Martin 
Schumacher/PH/Novartis)
        Subject:        Re: [BioC] RMA normalization when using subsets of samples
        Category: 



This would be a problem if one or more of the resulting subsets is small
and contains outliers.

My preference is to preprocess all arrays together. My reasoning is that
doing this will give RMA median polish (and to a lesser extent with the
quantile normalisation) steps much more information to work with.

Regards, Adai




On Wed, 2006-02-15 at 17:16 +0000, Wolfgang Huber wrote:
> Dear Sylvia,
> 
> this might not be the answer that you want to hear, but for the end 
> result it should not matter (substantially) which of the two 
> possibilities you take, and I would be worried if it did.
> 
> Best wishes
>   Wolfgang
> 
> -------------------------------------
> Wolfgang Huber
> European Bioinformatics Institute
> European Molecular Biology Laboratory
> Cambridge CB10 1SD
> England
> Phone: +44 1223 494642
> Fax:   +44 1223 494486
> Http:  www.ebi.ac.uk/huber
> -------------------------------------
> 
> Sylvia.Merk@ukmuenster.de wrote:
> > Dear bioconductor list,
> > 
> > I have a question concerning RMA-normalization:
> > 
> > There are for example 200 CEL-Files and the clinicians have several
> > research questions - each concernig only a subset of the 200 samples
> > including the possibility that some samples are included in more than
> > one question.
> > 
> > There are two possibilities to normalize the CEL-Files: 
> > 
> > 1.: Read all 200 chips in an affybatch-object and normalize all 200
> > chips together and further analyze the required subset. 
> > 
> > 2.: Read only the required chips in an affybatch-object, normalize 
these
> > chips and then perform further analysis 
> > I think that this approach is the better one but it has the 
disadvantage
> > that some samples are included in several normalizations ending in
> > different gene expression levels for a single sample.
> > 
> > What is (from a statisticians view) the appropriate approach to
> > normalize CEL-Files in this case?
> > 
> > Thank you in advance
> > Sylvia 
> >
> 
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