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Re: st: tetrachoric correlation in stata 9


From   Maarten buis <maartenbuis@yahoo.co.uk>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: tetrachoric correlation in stata 9
Date   Tue, 14 Nov 2006 21:02:24 +0000 (GMT)

--- prneiva <prneiva@terra.com.br> wrote:
> I am trying to run a tetrachoric correlation in Stata 9. After
> running tetrachoric varlist, available, the correlation matrix is
> shown on the screen but it looks like that nothing is being saved 
> on memory. Matrix list command shows that there is not any matrix
> in there.
> 
>  Stata's help says that the pairwise correlation matrix is returned
> as r(corr) and can be used to perform a factor or a principal
> component analysis of binary variables using factormat or pcamat. It
> also says tetrachoric saves the matrix r(Rho). What does it mean? 


Pedro:
Here is an example on how you could use 
-tetrachoric-, find the results that it 
leaves behind, and use the correlation 
matrix. Copy the example text, open  
Stata, type -doedit-, and paste the text
and than click on do.
HTH,
Maarten

*------------ begin example -----------
sysuse auto, clear

/*make some binary vars*/
gen good = rep78>3
sum price, meanonly
gen expensive = price>r(mean)


tetrachoric foreign good expensive
/*see what -tetrachoric- leaves behind*/
return list
matrix list r(Rho)

/*do the factor analysis*/
factormat r(Rho), n(74)
*------------- end example ------------



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

visiting adress:
Buitenveldertselaan 3 (Metropolitan), room Z434

+31 20 5986715

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


		
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