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

Stone, Gregory gstone at UTNet.UToledo.Edu
Sun Jun 1 20:46:34 EST 2008


I've done this several times when the N is too small.  My question regards local independence.  When I've done this in the past, I've (we've) assessed the items for overfit and exceptionally high point-biserials.  It isn't perfect, but it can give us an idea as to whether or not the requirement of local independence is met, even for the calculation of item difficulties.  Some journals are requiring this to be done.  So ...

Is this really important in the estimation process for the purpose of equating?  (local independence)

Overfitting items ... does the fit help us with detecting them?  What happens if you find them?



Gregory E. Stone, Ph.D., M.A.

Associate Professor of Research and Measurement
The Judith Herb College of Education
The University of Toledo, Mailstop #921
Toledo, OH 43606   419-530-7224

Editorial Board, Journal of Applied Measurement     www.jampress.org

Board of Directors, American Board for Certification of Teacher Excellence     www.abcte.org

For information about the Research and Measurement Programs at The University of Toledo and careers in psychometrics, statistics and evaluation, email gregory.stone at utoledo.edu.

-----Original Message-----
From: rasch-bounces at acer.edu.au on behalf of Mike Linacre (RMT)
Sent: Sat 5/31/2008 5:07 PM
To: rasch at acer.edu.au
Subject: [Rasch] Help with equating partial credit items in pre - post test
Thank you for your question, Andres.

Ben Wright at www.rasch.org/rmt/rmt101f.htm recommends using pre- and post- test data together to estimate the rating scale structure anchors. You can then anchor the rating scale structures, and use the post-test data to estimate the item anchors.

Rasch measures are remarkably robust against disordered thresholds (low frequency categories) so don't collapse categories if they are merely sampling effects (not due to structural flaws in the rating scale). 

Mike L.

At 5/31/2008, you wrote:

	Which could be the best way to put pre test results on the post test frame of reference?

Mike Linacre
Editor, Rasch Measurement Transactions
rmt at rasch.org www.rasch.org/rmt/ <http://www.rasch.org/rmt/>  Latest RMT:  21:4 Spring 2008

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