[Rasch] Rasch: analyze two versions of a test

Bond, Trevor trevor.bond at jcu.edu.au
Sat Jun 22 23:17:56 EST 2013


Dear Lucia
You do it both ways, expecting invariance.
Where you don't, you look for reasons.
Then choose.
TGB


Sent from 007's iPad

On 22/06/2013, at 12:19 PM, "Lucia Luyten" <Lucia.Luyten at arts.kuleuven.be<mailto:Lucia.Luyten at arts.kuleuven.be>> wrote:

Hi

I have a question about analyzing two versions of a test.

Say we have 130 items for a test. We make two versions of this test. In version A, we put items number 1 to 80 and in version 2 the items number 50 to 130. So items 50-80 are in both versions. In version A, the item numbers 1 to 30 are anchor items from a previous test. For these items, we know and use the measures from a previous Facets analysis. These anchor items (1-30) occur only in version A, not in version B.

About 400 candidates take version A, and about 250 take version B. The test is rated by 4 raters. Raters rate both versions, each test taker is rated by one random rater.

One might choose to take all candidates together for analysis. Or one can choose to first analyze version A separately (using the measures for the anchor items).  And then use the outcome, i.e. the measures for the identical items (number 50-80) and the measures for the raters, in the subsequent analyses of version B.

Which way of analyzing is preferable and why is it?

Kind regards,

Lucia Luyten


________________________________
Lucia Luyten
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CNaVT / CTO / KULeuven
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3000 Leuven
016 32 53 59
fax 016 32 53 60
lucia.luyten at arts.kuleuven.be<mailto:lucia.luyten at arts.kuleuven.be>
http://www.cnavt.org
www.cteno.be<http://www.cteno.be>




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