R help - May 2004 - factor analysis

hi all

this is a stats question.

when undertaking factor analysis should the variables included always be
continiuos random variables? could one include categorical data? e.g
some survey type data

my gut feeling is that one should not include categorical type data
since factor analysis is based on the eigenanalysis of the correlation
matrix of a group of variables. The introduction of categorical data
into a data set might "mess up" the corelation matrix.

Dear Allan,

I assume that the categorical data are ordinal. There are methods for
factor analyzing ordinal data (e.g., using polychoric correlations) and
mixed ordinal and interval data, but as far as I know, these aren't
implemented in R.

John

On Thu, 13 May 2004 18:32:11 +0200
 allan clark <allan at stats.uct.ac.za> wrote:
> hi all
> 
> this is a stats question.
> 
> when undertaking factor analysis should the variables included always
> be
> continiuos random variables? could one include categorical data? e.g
> some survey type data
> 
> my gut feeling is that one should not include categorical type data
> since factor analysis is based on the eigenanalysis of the
> correlation
> matrix of a group of variables. The introduction of categorical data
> into a data set might "mess up" the corelation matrix.
> 
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--------------------------------
John Fox
Department of Sociology
McMaster University
Hamilton, Ontario, Canada
http://socserv.mcmaster.ca/jfox/