[Rasch] Help with equating partial credit items in pre - post test

Stephen Humphry shumphry at cyllene.uwa.edu.au
Sun Jun 1 22:04:58 EST 2008


Hi Andrés.

Have you sought to understand the reason that the threshold estimates  
are disordered? I would share your concerns about validity, and would  
try to understand this first.

There is a typology of successfully and unsuccessfully polytomously  
scored mathematics items in a report that may be helpful in  
understanding the problem(s) indicated by disordering. Let me know if  
you'd like a copy and if so, I'll see if I can get it to you.

Kind regards,

Steve


Quoting Andrés Burga León <21781 at upch.edu.pe>:

> Hello to everybody on the list.
>
>
>
> I have some doubts about how to equate pre 7 post test results in a math
> test. I want to put the two measures on the post test frame of reference.
>
>
>
> The problem is that most of the items are politomous, scored on a 0 to 2
> scale, and the threshold are different for the pre / post test calibrations.
>
>
>
> On the pre test, most items show disordered Rasch – Andrich thresholds (most
> responses are 0 score, only few 1 or 2). In the post test, the situation for
> some items is contrary. There are also disordered thresholds, but the
> answers are concentrated on the 2 score).
>
>
>
> Other items, that showed disordered thresholds on the pre – test know show
> ordered Rasch- Andrich thresholds. I think that I should only use one of the
> thresholds in order to anchor the pre-test results, but I’m not sure about
> the effects of the differences in threshold structures on the validity of
> the measures
>
>
>
> Which could be the best way to put pre test results on the post – test frame
> of reference?
>
>
>
> Thank you very much for your advise
>
>
>
> Andres
>
>






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