Hi, I was wondering if anyone could tell me why prcomp() will "Invent" modes of variation in a PCA on identical replicates of data? I would have expected 50 (or whatever number) of identical replicates to return a null score in such an analysis (or at the least, all variables would share the same PC score). This is not the case and I was wondering could someone point me in the direction of some literature to explain the reason behind this? Laura Quinn Institute of Atmospheric Science School of Earth and Environment University of Leeds Leeds LS2 9JT tel: +44 113 343 1596 fax: +44 113 343 6716 mail: laura at env.leeds.ac.uk
If you don't get a response: reproducible example, please. I suspect that you're looking at numerical analysis artifacts, assuming I have correctly interpreted you. -- Bert Gunter Genentech Non-Clinical Statistics South San Francisco, CA "The business of the statistician is to catalyze the scientific learning process." - George E. P. Box> -----Original Message----- > From: r-help-bounces at stat.math.ethz.ch > [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Laura Quinn > Sent: Wednesday, February 08, 2006 9:50 AM > To: r-help at stat.math.ethz.ch > Subject: [R] slightly off-topic re prcomp() > > Hi, > > I was wondering if anyone could tell me why prcomp() will > "Invent" modes > of variation in a PCA on identical replicates of data? I would have > expected 50 (or whatever number) of identical replicates to > return a null > score in such an analysis (or at the least, all variables > would share the > same PC score). This is not the case and I was wondering could someone > point me in the direction of some literature to explain the > reason behind > this? > > Laura Quinn > Institute of Atmospheric Science > School of Earth and Environment > University of Leeds > Leeds > LS2 9JT > > tel: +44 113 343 1596 > fax: +44 113 343 6716 > mail: laura at env.leeds.ac.uk > > ______________________________________________ > R-help at stat.math.ethz.ch mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide! > http://www.R-project.org/posting-guide.html >
On 2/8/2006 12:50 PM, Laura Quinn wrote:> Hi, > > I was wondering if anyone could tell me why prcomp() will "Invent" modes > of variation in a PCA on identical replicates of data? I would have > expected 50 (or whatever number) of identical replicates to return a null > score in such an analysis (or at the least, all variables would share the > same PC score). This is not the case and I was wondering could someone > point me in the direction of some literature to explain the reason behind > this?I think you'll need to show us an example. I just tried what I think you described, and got all the components with 0 standard deviation, as I would have expected. Duncan Murdoch> > Laura Quinn > Institute of Atmospheric Science > School of Earth and Environment > University of Leeds > Leeds > LS2 9JT > > tel: +44 113 343 1596 > fax: +44 113 343 6716 > mail: laura at env.leeds.ac.uk > > ______________________________________________ > R-help at stat.math.ethz.ch mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html