Date: Wed, 10 Oct 2007 17:32:07 -0700
Sender: "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From: Song <sounpra@YAHOO.COM>
Subject: Re: PCA using SAS and R
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On Oct 10, 4:23 pm, peterflomconsult...@mindspring.com (Peter Flom)
> Song <soun...@YAHOO.COM> wrote
> >Can anyone please explain to me how running a simple PCA in SAS and R
> >can produce conflicting results? You will notice that signs of the
> >component score are different only in the 4th component. What is
> >troubling to me is that this is not consistent. On a different
> >dataset, the signs become different starting with the 2nd component.
> The signs of the principal components are arbitrary. It's like saying "John is taller than Mary" or "Mary is shorter than John".
> If the magnitudes were noticeably different, that would be troubling, but changes in the signs are no big deal
Hi Peter --
I understand what you are saying...however this does matter if I'm
trying to construct biplots using say the first two PCs. This
wouldn't be a problem if I knew a priori that the sign will differ
only after the second component...but it changes for different
dataset. So the biplots that I get from SAS and R may or may not be