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# Re: st: calculate alpha after polychoric factor analysis

 From Stas Kolenikov To statalist@hsphsun2.harvard.edu Subject Re: st: calculate alpha after polychoric factor analysis Date Mon, 13 Feb 2012 09:34:06 -0500

```I am not sure -alpha- is entirely appropriate in this situation. Tenko
Raykov published a number of papers in late 1990s conceptualizing
composite reliability extending the alpha to more general situations
of factor analysis. I don't know if any of that is implemented as a
third party package. Obviously, this is doable as -nlcom- following
-sem- or -confa-, although you would need to spend some time figuring
out how to best use either the estimated coefficients or the resulting
matrices.

Note also that -polychoric- computes correlations in pairwise fashion,
so there may be no single sample size that is suitable for factor
analysis (although this is probably just a scaling coefficient
somewhere, as the eigenvalues and eigenvectors produced in factor
analysis do not depend on -n-).

On Mon, Feb 13, 2012 at 8:54 AM,  <Seyi.Soremekun@lshtm.ac.uk> wrote:
> Dear Stata Listers,
>
> I would like to estimate the equivalent of  Cronbach's alpha after factor analysis conducted on a polychoric matrix of ordinal, Likert items. I started out in a pretty standard way thus:
>
> polychoric var1 - var29
> display r(sum_w) // check number of respondents answered all = 331
> matrix r = r(R)
> factormat r, n(331) factors(3) ipf
> alpha?
>
> Is there such functionality available, or might I have to re-do the whole analysis in R or SAS?
>
> thanks,
>
> Seyi
>
>
> Dr Seyi Soremekun
> Faculty of Epidemiology and Public Health
> London School of Hygiene and Tropical Medicine
> London WC1E 7HT
> +442079272464
>
>
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--
Stas Kolenikov, also found at http://stas.kolenikov.name
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```