[R] Factor rotation (e.g., oblimin, varimax) and PCA

Mark Difford mark_difford at yahoo.co.uk
Thu Jan 27 08:02:11 CET 2011


>> But when I use 'principal' I do not seem to be able to get the same
>> results 
>> from prcomp and princomp  and a 'raw' use of eigen:
< ...snip... >
>> So what is wrong with the rotations and what is wrong with 'principal'?

I would say that nothing is wrong. Right at the top of the help file for
principal() [3rd line down] Professor Revelle notes that

"The eigen vectors are rescaled by the sqrt of the eigen values to produce
the component loadings more typical in factor analysis."

You talk about differences and results not "quite" corresponding. But what
actually are these differences? and what are their magnitudes? In cases like
this, where you are questioning well-tested functions you would be well
advised to give concrete examples, accompanied by code that users can run
without having to grub around your questions.

Regards, Mark.

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