hi everyone

sorry to bother with a simple question: In biplot of a principal component
analysis the graphic shows four axis, everyone with a different scale, I
guess that "x" and "y" axis (lower and left axis)  are related with the
scores of the first two principal components, however I don´t understand
the other two axis (upper and right) and what information are they giving
to me (i. e. what complementary information are they giving to me in
addition of what lower and left axis tell me), and what are the units in
wich this axis are?

I put here an example, where I made the biplot and the graphic for the
scores of the fisrt two principal components, and I don´t get why the units
are so different.

thanks a lot

par(mfrow=c(1,2))
data(USArrests)
k<-USArrests; k<-edit(k)
a<-prcomp(k, scale = TRUE) #make PCA
ñ<-a$x[,1:2]  #scores of the fist 2 components
biplot(a, cex=c(0.5,0.5)) # biplot
plot(ñ, pch="", main="scores"); text(ñ, rownames(k), cex=0.5)  #plot scores
summary(ñ) #summary of scores, units in same scale as in scores graphic
#but different form biplot graphic,  however in both graphics points are in
the same position


Daniel

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