[R] PCA and categorical data

[(Ted Harding)]

On 06-Mar-09 09:25:26, Prof Brian Ripley wrote:
> You might want to look into correspondence analysis, which has several 
> variants of PCA designed for categorical data.

In particular, have a look at the results of

  RSiteSearch("correspondence")

Ted.

> On Fri, 6 Mar 2009, Galanidis Alexandros wrote:
> 
>> Hi all,
>>
>> I' m trying to figure out if it is appropriate to do a PCA having only
>> categorical data (not ordinal). I have only find the following quote:
>>
>> One method to find such relationships is to select appropriate
>> variables and
>> to view the data using a method like Principle Components Analysis
>> (PCA) [4].
>> This approach gives us a clear picture of the data using KL-plot of
>> the PCA.
>> However, the method is not settled for the data including categorical
>> data.
>> [http://hp.vector.co.jp/authors/VA038807/personal/covEigGiniRep17.pdf]
>>
>> but I'm still not sure if it WRONG to do so.
> 
> Since normally categorical data is taken to be binomial or Poisson 
> distributed, the variance varies with the mean and least-squares (the 
> basis of PCA) is then sub-optimal.  Correspondence analysis takes that 
> into account (at least to some extent).
> 
>> Any opinion or reference would be very helpful
> 
> There is a basic introduction in MASS4, with references to more 
> comprehensive accounts.
> 
>> thanks
>>
>> ______________________________________________
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>>
> 
> -- 
> Brian D. Ripley,                  ripley at stats.ox.ac.uk
> Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
> University of Oxford,             Tel:  +44 1865 272861 (self)
> 1 South Parks Road,                     +44 1865 272866 (PA)
> Oxford OX1 3TG, UK                Fax:  +44 1865 272595
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

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E-Mail: (Ted Harding) <Ted.Harding at manchester.ac.uk>
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Date: 06-Mar-09                                       Time: 09:46:15
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