> -----Original Message-----
> I avoid the biplot at all costs, because IMHO it violates one
> of the tenets of good graphic design: It has two entirely
> different scales on axes. These are maximally confusing to
> the end-user. So I never use it.
I think you're being unnecessarily restrictive there. The confusion that arises
when using multiple scales in the same graphical dimension arises from a
tendency to read distances and locations on the wrong scale. In a biplot, the
PC's have essentially no intuitive physical interpretation (by which I mean a
1:1 mapping onto an identifiable variable) so this doesn't matter much even if
it happens (in fact you cold probably lose the scales entirely in a biplot
without compromising its interpretation much). And the alternative - sticking
rigidly to the 'one axis per dimension' rule and to plot them with the _same_
scales - often leads to unreadable plots: invisibly tiny arrows or an invisibly
tiny cloud of data points.
But having indicated that I don't see a biplot's multiple scales as
particularly likely to confuse or mislead, I'm always interested in
alternatives. The interesting question is 'given the same objective - a
qualitative indication of which variables have most influenced the location of
particular data points (or vice versa) and in which general direction - what do
you suggest instead?'
Steve Ellison
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