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st: PCA, reverse scorings


From   Juan Julio Gutierrez <juanju@yahoo.com>
To   Juan Julio Gutierrez <juanju@yahoo.com>, statalist@hsphsun2.harvard.edu
Subject   st: PCA, reverse scorings
Date   Thu, 27 Dec 2007 09:07:33 -0800 (PST)

> Dear all, 
 
 
> I am working on creating an index using PCA. 
> When running PCA the first time, with the original variable values, the loadings come up with
some unexpected signs

 KI index loadings	
 original variables	

 skillw	-0.51811
 eduatt	0.576
 rd	0.55153
 itexp	-0.30919
 
I would expect that skillw and itexp would have positive values affecting the new variable I
create with the command score (I am susing STATA 8). 

Reverse scoring: I have multiplied both variables (skillw and itexp) by -1 to get the opposite
sign. the results now are: 

 KI index loadings	
 	
 newskillw	0.51811
 eduatt	         0.576
 rd	         0.55153
 newitexp	0.30919
  
Now I get loadings that make sense. However when using the score command to save the loadings and
listing the values, both new variables (i.e. w. original variables and with opposite sign) are
exactly the same. 
 
 I would assume that the values should be different providing the different signs of the
loadings.
Could anybody help me clarify this? 
 
Thanks a lot

Juan Julio Gutierrez
George Mason University
 
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