# Re: st: tetrachoric correlation in stata 9

 From "Daniel Stegmueller" To statalist@hsphsun2.harvard.edu Subject Re: st: tetrachoric correlation in stata 9 Date Tue, 14 Nov 2006 23:27:19 +0100

Additional to Maarten's suggestion you can use :

*------------------------------------
sysuse auto, clear

gen good = rep78>3
sum price, meanonly
gen expensive = price>r(mean)

tetrachoric foreign good expensive
matrix C = r(Rho)
local n = r(N)

factormat C, n(`n')
*--------------------------------------------

This way you don't have to type in the number of cases by hand - which
comes in handy when you're using loops for example....

Best,
Daniel

2006/11/14, Maarten buis <maartenbuis@yahoo.co.uk>:
--- 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

Buitenveldertselaan 3 (Metropolitan), room Z434

+31 20 5986715

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

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