On 11-09-09 5:42 AM, René Mayer wrote:
thanks for pointing out Paul,
but the thing which is annoying me in the first place IS this
direction reversal.
this makes no sense for me
why could this be?
I think you need to read more about principal components. The signs
within a PC vector are meaningful only relative to each other (e.g. most
of the variation in the variables is in the same direction: as
standardized murder rates increase, the others increase by approximately
the same amount), but switching all of the signs within a vector gives
the same meaning (e.g. as murder decreases, all of the others decrease).
Duncan Murdoch
Zitat von "Paul Hiemstra"<paul.hiems...@knmi.nl>:
Hi,
If all the signs are switched the PC's are still the same. The principal
vectors are along the same axis, only in a different direction. So there
is no problem :).
hope this helps,
Paul
On 09/09/2011 09:01 AM, René Mayer wrote:
Dear All,
when I'm running a PCA with
prcomp(USArrests, scale = TRUE)
I get the right principal components, but with the wrong sign infront
Rotation:
PC1 PC2 PC3 PC4
Murder 0.5358995 -0.4181809 0.3412327 0.64922780
Assault 0.5831836 -0.1879856 0.2681484 -0.74340748
UrbanPop 0.2781909 0.8728062 0.3780158 0.13387773
Rape 0.5434321 0.1673186 -0.8177779 0.08902432
instead of
PC1 PC2 PC3 PC4
Murder -0.5358995 0.4181809 -0.3412327 0.64922780
Assault -0.5831836 0.1879856 -0.2681484 -0.74340748
UrbanPop -0.2781909 -0.8728062 -0.3780158 0.13387773
Rape -0.5434321 -0.1673186 0.8177779 0.08902432
what is happening here?
any ideas?
thanks,
René
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Global Climate Division
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