[Rasch] CAT Questions

ranganaths ranganath.s at excelindia.com
Fri Jan 29 22:28:10 EST 2010



            Thanks for the response. I am referring to the book THE BASICS
OF ITEM RESPONSE THEORY by Frank Baker. In this book he says. I quote

"There are three different item characteristic curve models to choose from
and several different ways to implement the Birnbaum paradigm. From these,
the author has chosen to present the approach based upon the one-parameter
logistic (Rasch) model as implemented by Benjamin Wright and his coworkers
in the BICAL computer program. Under this model, each item has only one
parameter to be estimated. The procedures work well with small numbers of
test items and small numbers of examinees."


            We have a product which administers tests to thousands of people
and having hundreds of Items in the test. The above quote gives a warning
for such kind of applications. I wish to know If this is true which model
should be used for the kind of tests we are administering? Thanks once again
for the response.




Ranganath S


From: Mike Linacre (RMT) [mailto:rmt at rasch.org] 
Sent: Friday, January 29, 2010 2:29 AM
To: ranganaths
Subject: RE: [Rasch] CAT Questions


Thank you for your further questions, Ranganath.

1. and 2. - No and No.  No need to pre-calibrate. No need to pre-administer.
See, for instance, www.rasch.org/rmt/rmt52b.htm "CAT with a Poorly
Calibrated Item Bank". But the initial results will be approximate (but
useful) until you have collected enough data to properly calibrate the item
bank. See also www.rasch.org/memo69.htm and www.rasch.org/memo40.htm

3. and 4. - What is the "conventional methodology"?  Is it Classical Test
Theory (CTT, linear analysis of scored test responses) or Paper-and-Pencil
(PAP) tests?

Rasch methodology can have considerable advantages over CTT.
CAT can have considerable advantages over PAP.
But the advantages depend on the situation.

For instance, in remedial teaching, you can combine a Rasch-based CAT test
with computerized instruction, so that the student is automatically tutored
on the topic-areas for which the CAT test reports poor performance.

Mike L.

At 1/28/2010, you wrote:

     Thanks for the response. I still have a doubt about the practical
implementation of the IRT. 

1. Lets assume that I have started IRT from scratch. I have a list of
questions to be administered to a group. For each of the question I know
only whether the question is easy, medium or hard, the values of   

    the item parameters are unknown for me. Is it required to calibrate the
items in the test and find out the item parameters before it is
administered? If yes

2. Is it required to administer each and every new item to a sample group
ascertaining the item parameters before it is given to the real examinees?

3. What advantage does the IRT implementation gives to the tutor who is
supposed to take the remedial teaching, which anyway can also be taken from
any kind of conventional testing methodology?

4. I have read in an article that the CAT helps in reducing the test timings
and also it could be administered at time independent fashion still
measuring the examinees ability on the same scale, Are these the only
advantages of using IRT? IF any other advantage is there over the
conventional methodology please explain.



Ranganath S

Mike Linacre
Editor, Rasch Measurement Transactions
rmt at rasch.org www.rasch.org/rmt/ Latest RMT:  23:2 Autumn 2009

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