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st: RE: Cluster analysis -similarity and dissimilarity measures


From   "Nick Cox" <n.j.cox@durham.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: Cluster analysis -similarity and dissimilarity measures
Date   Tue, 24 Oct 2006 16:04:30 +0100

I am not aware of specific provision for ordinal 
variables. In many circles part of the definition of 
an ordinal variable is that the measurement scale
falls short of metric properties, so that the 
existence of a similarity or dissimilarity metric 
would appear arguable at best. 

In some circumstances, it might be useful to 
convert data to ranks or -- in this case --
something similar like "ridits". 

Or, you could just say, code them 1 to 4 and 
feed them in and see what comes out, being 
aware of the arbitrariness of that. 

There is cute stuff in Persi Diaconis' monograph
on group theory and statistics that might apply 
here, but I'd be surprised at a Stata implementation. 
Like the North Face of the Eiger, this material
is better approached from behind, e.g. through 
Marden's book on rank data. 

Diaconis, P. 1988. Group Representations in Probability and
Statistics. Hayward, CA: Institute of Mathematical Statistics. 

Marden, J.I. 1995. Analyzing And Modeling Rank Data.
London: Chapman and Hall. 

Nick 
n.j.cox@durham.ac.uk 

Kallimanis, Bellinda
 
> I have a question about the measure options for conducting 
> hierarchical
> cluster analysis. I see that there are measures for continuous and
> binary variables, but what about ordinal variables? Is there a measure
> available in stata that I can use and just can't find? Or should I do
> some sort of standardization of the variables? The variables have 4
> categories. 

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