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Tree with ordinal independent variable

To: <s-news@lists.biostat.wustl.edu>
Subject: Tree with ordinal independent variable
From: "Peter Flom" <flom@ndri.org>
Date: Thu, 30 Jan 2003 10:57:56 -0500
Hello

I am running S-Plus 6 on a Windows machine.

I am trying to fit a classification tree with independent variables
that are ordinal.  However the result does not take the ordinalaity of
the variables into account.  e.g., one variable has levels A through H. 
I have made this an ordinal factor in the data window.  But the tree
gives splits such as 

AC   BDEFGH

I had thought of perhaps numericizing the scale, but this doesn't seem
ideal to me.  Is there a better solution?

Thanks in advance

Peter



Peter L. Flom, PhD
Assistant Director, Statistics and Data Analysis Core
Center for Drug Use and HIV Research
National Development and Research Institutes
71 W. 23rd St
New York, NY 10010
(212) 845-4485 (voice)
(917) 438-0894 (fax)


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