Re: st: Creating Scale with Ordinal Data using IRT

[Jean-Benoit Hardouin <jean-benoit.hardouin@univ-nantes.fr>]

Thank you Ronan,
To respond to the questions of  an anonymous statalister 
(gz6931@albany.edu) [It always is unpleasant to respond to anonymous 
persons !] and several remarks posted today:
   - Item Responses Models allows considering binary AND ordinal items. 
The Rating Scale Model, The Partial Credit Model and the Graded 
Responses Model are the more famous models for ordinal responses
   - All the models of the Item Responses Theory (IRT) can be 
considered as Generalized Linear Mixed Models, and the parameters can be 
estimated with GLLAMM, or for the Rasch model by -xtlogit- or -clogit- 
(for the fixed effets Rasch model) [see 
http://www.stata.com/support/faqs/stat/rasch.html for details on 
technical aspects)
   - There is some specific modules under Stata for the Item Response 
Theory, for example -raschtest- (ssc describe raschtest) wich allows 
estimating the parameters of the Rasch model AND to evaluate the fit of 
the model to the data (IRT requires specific fit tests)
   - I don't know specific Stata modules to run polytomous IRT models 
but the GLLAMM manual explains how the parameters of a Partial Credit 
Model can be estimated with GLLAMM and the ologit link 
(http://www.gllamm.org)[I admit to using SAS to do that ! Bouuuuh]
   - In  IRT, there is full and full specific software. For several 
years, more and more works are realised on  generalist software like 
Stata, R and SAS. The module -raschtest- certainly made Stata the more 
powerfull software (among these 3 ones) to run and test a Rasch model, 
but concerning polytomous models, there is no specific modules under 
Stata and SAS (proc NLMIXED) is more easy to use for that !! For a 
database of existing Stata modules, SAS macro-programs and R library in 
the field of IRT, see the FreeIRT website at http://freeirt.anaqol.org
Best regards,
Jean-Benoit Hardouin
--
Jean-Benoit Hardouin
University of Nantes - Faculty of pharmaceutical sciences
France
jean-benoit.hardouin@univ-nantes.fr
http://www.anaqol.org

Ron�n Conroy a �crit :


> On 11 Ean 2007, at 15:57, gz6931@albany.edu wrote:
>
> > What commands might I use to create one scale for each person using  IRT
> > based on the responses to the 5 items?
> Have a look at Jean-Benoit Hardouin's excellent site, http://anaqol.org/
>
> He's got a treasure trove of Stata resources for IRT.
>
>
>
> =========
> Ron�n Conroy
> Royal College of Surgeons in Ireland
> rconroy@rcsi.ie
> +353 (0) 1 402 2431
> +353 (0) 87 799 97 95
> http://www.flickr.com/photos/ronanconroy
>
>
>
>
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