[R] scale or not to scale that is the question - prcomp
petr.pikal at precheza.cz
Wed Aug 19 15:02:49 CEST 2009
Duncan Murdoch <murdoch at stats.uwo.ca> napsal dne 19.08.2009 14:49:52:
> On 19/08/2009 8:31 AM, Petr PIKAL wrote:
> > Dear all
> I would say the answer depends on the meaning of the variables. In the
> unusual case that they are measured in dimensionless units, it might
> make sense not to scale. But if you are using arbitrary units of
> measurement, do you want your answer to depend on them? For example, if
> you change from Kg to mg, the numbers will become much larger, the
> variable will contribute much more variance, and it will become a more
> important part of the largest principal component. Is that sensible?
Basically variables are in percentages (all between 0 and 6%) except dus
which is present or not present (for the purpose of prcomp transformed to
0/1 by as.numeric:). The only variable which is not such is iep which is
basically in range 5-8. So ranges of all variables are quite similar.
What surprises me is that biplot without scaling I can interpret by used
variables while biplot with scaling is totally different and those two
pictures does not match at all. This is what surprised me as I would
expected just a small difference between results from those two settings
as all numbers are quite comparable and does not differ much.
> Duncan Murdoch
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