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st: Standardization of Ordinal Variables and Polychoric PCA for Index


From   "Hisako Kobayashi" <hisakoko@usc.edu>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: Standardization of Ordinal Variables and Polychoric PCA for Index
Date   Tue, 23 Jun 2009 23:14:33 -0700

Dear Statalist:

I want to know how to develop an index from 5 ordinal variables. But I am not sure about standardization of ordinal variables and how to use weights to develop an index.  The ordinal variables are in Likert scale from 1 to 4. 

I am thinking of using eigenvectors of the first component of polychoric PCA (with code of 'polychoricpca').  I believe that this code is for ordinal variables so that I don't need to standardize the variables before I run polychoric PCA. ( Before I run polychoric PCA, I checked Kendall tau b and MCA.).

But after that, I think that I need to standardize ordinal variables to calculate the index with weights (eigenvectors). If so, how can I standardize ordinal variables? And then I multiply each variable by weight from the pca and sum up to make an index.  

I want to know if this procedure is correct or not. This index is one of explanatory variables. I just want to know a simple method to develop an index.

Thank you very much for your help in advance.
Best regards,

Hisako


--
********************************
Hisako Kobayashi
hisakoko@usc.edu
Ph.D Candidate in Public Administration
School of Policy, Planning and Development University of Southern California
********************************



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