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From |
Cameron McIntosh <cnm100@hotmail.com> |

To |
STATA LIST <statalist@hsphsun2.harvard.edu> |

Subject |
RE: st: calculate alpha after polychoric factor analysis |

Date |
Tue, 14 Feb 2012 21:58:08 -0500 |

You may also want to see a more recent paper: Gadermann, A.M., Guhn, M., & Zumbo, B.D. (2012). Estimating ordinal reliability for Likert-type and ordinal item response data: A conceptual, empirical, and practical guide. Practical Assessment, Research & Evaluation, 17(3). http://pareonline.net/pdf/v17n3.pdf Cam ---------------------------------------- > From: jcoveney@bigplanet.com > To: statalist@hsphsun2.harvard.edu > Subject: Re: st: calculate alpha after polychoric factor analysis > Date: Wed, 15 Feb 2012 11:54:31 +0900 > > Seyi Soremekun wrote: > > Thanks (and for the polychoric command itself). The sample size is not an issue > - all respondents answered all the questions, displaying -n- was just a check > for me (if that is what you meant in your note?) > > I'm not sure about the appropriateness of using alpha either, however, I know > that ordinal alphas are available in other types of software (Basto and Pereira > 2012 J. Statistical Software 46(4)), and wondered if there was something I could > use in Stata. > I was hoping that I could ask stata to calculate the alpha on the saved matrix > rather than a list of variables. > > -------------------------------------------------------------------------------- > > The Basto and Pereira article references Bruno D. Zumbo, Anne M. Gadermann and > Cornelia Zeisser, Ordinal Versions of Coefficients Alpha and Theta for Likert > Rating Scales. _Journal of Modern Applied Statistical Methods_ 6(1): 21--9, > 2007), which in turn references earlier work for the formula it displays for > ordinal coefficient alpha. If I've got the formula correctly implemented below, > then you can try something like what is illustrated. It shouldn't be too > difficult to morph it into an ado-file, but you'd probably want to verify its > correctness with a couple of worked examples. > > Joseph Coveney > > version 11.2 > > set more off > set seed `=date("2012-02-14", "YMD")' > tempname C > matrix define `C' = I(4) * 0.45 + J(4, 4, 0.55) > drawnorm latent1 latent2 latent3 latent4, corr(`C') double n(100) clear > forvalues i = 1/4 { > generate double u`i' = normal(latent`i') > generate byte manifest`i' = 0 > quietly forvalues cut = 0.2(0.2)0.8 { > replace manifest`i' = manifest`i' + 1 if u`i' > `cut' > } > } > polychoric manifest* > matrix define `C' = r(R) > factormat `C', n(100) factors(1) > > tempname L Psi > matrix define `L' = e(L) > matrix define `Psi' = e(Psi) > > local p = rowsof(`L') > > tempname f f2 u2 > scalar define `f' = 0 > scalar define `f2' = 0 > scalar define `u2' = 0 > forvalues i = 1/`p' { > scalar define `f' = `f' + `L'[`i', 1] > scalar define `f2' = `f2' + `L'[`i', 1] * `L'[`i', 1] > scalar define `u2' = `u2' + `Psi'[1, `i'] > } > scalar define `f' = `f' / `p' > scalar define `f2' = `f2' / `p' > scalar define `u2' = `u2' / `p' > > tempname pf2 > scalar define `pf2' = `p' * `f' * `f' > scalar define alpha = `p' / (`p' - 1) * /// > (`pf2' - `f2') / (`pf2' + `u2') > > display in smcl as text "Ordinal alpha = " as result %06.4f alpha > > alpha latent* > alpha manifest*, std > > exit > > > * > * For searches and help try: > * http://www.stata.com/help.cgi?search > * http://www.stata.com/support/statalist/faq > * http://www.ats.ucla.edu/stat/stata/ * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**Follow-Ups**:**RE: st: calculate alpha after polychoric factor analysis***From:*Cameron McIntosh <cnm100@hotmail.com>

**References**:**st: calculate alpha after polychoric factor analysis***From:*<Seyi.Soremekun@lshtm.ac.uk>

**Re: st: calculate alpha after polychoric factor analysis***From:*Stas Kolenikov <skolenik@gmail.com>

**Re: st: calculate alpha after polychoric factor analysis***From:*<Seyi.Soremekun@lshtm.ac.uk>

**Re: st: calculate alpha after polychoric factor analysis***From:*"Joseph Coveney" <jcoveney@bigplanet.com>

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