Ignore that advice and the agreement on allstat. It’s a mad idea and indicates they were not listening/reading.
Codes in a nominal variable are quite arbitrary – why not 1-European 2=Asian 33=American? You should NEVER do arithmetic on such a variable. What you do to include nominal values in a model is to split each value off as a binary (or dummy) variable, usually coding positive as 1: American 0/1; European 0/1 etc. Note you can leave one category out, as 0-0-0 means not American or European or ...
If your data is mainly categorical, check if PCA is appropriate.
Allan
From: A UK-based worldwide e-mail broadcast system mailing list [mailto:[log in to unmask]] On Behalf Of Angelica Neisa
Sent: 06 March 2013 15:52
To: [log in to unmask]
Subject: Categorical data in PCA and MDS
Hello everyone,
I'm working on PCA and MDS models for my data. But one of the variables is categorical (1:American, 2:European....) . I believe that I shouldn't put this variable in my model, but a statistician friend of mine told me to standardized it (X-M/s) and include it. What do you think?
Thanks,
Angelica
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