Statalist


[Date Prev][Date Next][Thread Prev][Thread Next][Date index][Thread index]

Re: st: PCA, reverse scorings


From   Maarten buis <maartenbuis@yahoo.co.uk>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: PCA, reverse scorings
Date   Thu, 27 Dec 2007 20:11:43 +0000 (GMT)

The two factors should be exactly the same. The original factor is
created using the folowing formula:

F1 = -0.51811*skillw + 0.5766*eduatt + 0.55153*rd + -0.30919*itexp	

The new factor is created using the following formula:

F2 = 0.51811*-1*skillw + 0.5766*eduatt + 0.55153*rd + 0.30919*-1*itexp

The two formulae are exactly the same.

-- Maarten

--- Juan Julio Gutierrez <juanju@yahoo.com> wrote:
> 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.


-----------------------------------------
Maarten L. Buis
Department of Social Research Methodology
Vrije Universiteit Amsterdam
Boelelaan 1081
1081 HV Amsterdam
The Netherlands

visiting address:
Buitenveldertselaan 3 (Metropolitan), room Z434

+31 20 5986715

http://home.fsw.vu.nl/m.buis/
-----------------------------------------


      ___________________________________________________________
Support the World Aids Awareness campaign this month with Yahoo! For Good http://uk.promotions.yahoo.com/forgood/
*
*   For searches and help try:
*   http://www.stata.com/support/faqs/res/findit.html
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/



© Copyright 1996–2021 StataCorp LLC   |   Terms of use   |   Privacy   |   Contact us   |   What's new   |   Site index