[Rasch] Validity in Rasch

Svend Kreiner S.Kreiner at biostat.ku.dk
Wed Mar 23 22:07:52 EST 2011


Why can't we have it both ways?

The assumptions of the Rasch model defines sound (and therefore also 
valid) measurement
*/and/*
the assumptions have to be tested because we do not have sound 
measurement if they are violated.

There really is no conflict.

What we may disagree about is what to do when items do not fit the model.

In such cases we have three options:

1) Purification by elimination of items that do not fit the model,
2) Modelling the departure from the model. This is what they do in RUMM 
when they split items
3) Use the Rasch model anyway, hoping that measurement is robust to the 
item-model misfit.

Best

Svend

Den 23-03-2011 02:00, Jim Sick skrev:
> Juanito,
>
> I've written a short online article dealing with the "assumptions" of
> the Rasch model, in which I recommend that we avoid thinking of them as
> "assumptions which need to be tested a priori," as is the case for
> statistical tests like ANOVA. It is often better to think of Rasch
> assumptions as "requirements" of sound measurement. A primary goal of a
> Rasch analysis is to determine to what degree the requirements (or
> assumptions) have been approximated. Read my article here, if you like.
> It may not answer your questions directly, but will give you a better
> overview.
>
> http://jalt.org/test/sic_5.htm
>
> Best
> Jim Sick
> Tokyo
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-- 
Svend Kreiner
Professor
Department of Biostatistics
University of Copenhagen

Øster farimagsgade 5, entr. B
P.O. Box 2099
DK-1014 Copenhagen K, Denmark

Email: S.Kreiner at biostat.ku.dk
Phone: (+45) 35 32 75 97

Fax: (+45) 35 32 79 07

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