[Rasch] Why Rasch?

Svend Kreiner svkr at sund.ku.dk
Tue Nov 8 22:12:39 EST 2011


Hi all,

For me, as a statistician, it is the sufficiency of the score which is 
the most important feature of the Rasch model.

Why?

For several reasons.

It justifies data reduction where you replace the multivariate item 
response profile by the total score and therefore simplifies both 
measurement (estimation of person parameters) and the statistical analyses.

It is because of the sufficiency that we are able to separate items from 
person by conditioning and therefore do not have to assume anyting about 
the distribution and/or sampling of persons.

For the same reason, it gives us much stronger tools for testing the fit 
of item responses to the model than we have for other models. This means 
that we stand on much firmer ground when we have tested and accepted the 
model than users of other IRT models and users of confirmatory factor 
analysis.

The posibility of doing serious model testing with the Rasch model may, 
by the way, be one of the reasons why some researchers prefer the 2- and 
3-parameters models. It is of course easier to accept these models 
because they have one or two extra parameters, but they are first of all 
easier to accept, because we do not have the same kind of powerful fit 
statistics for these models as we have for the Rasch models.

Svend

Den 08-11-2011 09:18, Anthony James skrev:
> Dear all,
> Reviewers of a journal have asked me to provide reasons why I have 
> used Rasch model for validating a questionnaire and notother methods. 
> Can you please tell me what should be written when one is asked such a 
> question?
> Cheers
> Anthony

-- 
*Svend Kreiner*
Professor

*Københavns Universitet*
Biostatistisk Afdeling
Det Sundhedsvidenskabelige Fakultet
Institut for Folkesundhedsvidenskab
Øster Farimagsgade 5, Opg. B
Postboks 2099, 1014 København K
DANMARK

TEL 35 32 75 97
FAX 35 32 79 07
LOK 10.2.09
_svkr at sund.ku.dk_
_www.biostat.ku.dk_


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