[Rasch] CAT Questions

ranganaths ranganath.s at excelindia.com
Sat Jan 30 17:58:34 EST 2010



            Thanks for the reply. I still have a question on CAT. Now with
all the mail Interactions I have understood that there is no need to
pre-administer the tests to rate Examinees. I have read that both the Item
parameters and the abilities of the examinees can be simultaneously obtained
using Birnbaum paradigm.  I hope the same is used in Winstep to ascertain
the abilities as well as the item parameters. 

I have read in a magazine futureGov that it reduces the time of test based
on the ability of the examinee. I assumed that it might start from some
basic item and go till the point till his ability is ascertained. If this is
one of the advantages of the CAT does it require computing the item
parameters in prior? If it is required to compute the item parameters in
prior, it require the test to be administered to sample examinees before
doing that. Is this true.



Ranganath S



From: Agustin Tristan [mailto:ici_kalt at yahoo.com] 
Sent: Friday, January 29, 2010 9:05 PM
To: ranganaths; Rasch
Subject: RE: [Rasch] CAT Questions


Hello, I can explain because I have worked in the translation of Baker´s
book and the adaptation of software into Spanish. The quote concerning the
limitations is clearly related to the program and the algorithms included in
the software by Baker provided with the book, but not to the Rasch model
itself. You may use a software like Winsteps without problems with more than
several thousands of persons!


Agustin Tristan



Ave. Cordillera Occidental  No. 635
Colonia  Lomas 4ª San Luis Potosí, San Luis Potosí.
C.P.  78216   MEXICO
 (52) (444) 8 25 50 76
 (52) (444) 8 25 50 77
 (52) (444) 8 25 50 78
web page (in Spanish):  <http://www.ieia.com.mx/> http://www.ieia.com.mx

web page (in English) http://www.ieesa-kalt.com/English/Frames_sp_pro.html

--- On Fri, 1/29/10, ranganaths <ranganath.s at excelindia.com> wrote:

From: ranganaths <ranganath.s at excelindia.com>
Subject: RE: [Rasch] CAT Questions
To: "'Mike Linacre (RMT)'" <rmt at rasch.org>
Cc: rasch at acer.edu.au
Date: Friday, January 29, 2010, 5:28 AM



            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,  <http://www.rasch.org/rmt/rmt52b.htm>
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
<http://www.rasch.org/memo69.htm> www.rasch.org/memo69.htm and
<http://www.rasch.org/memo40.htm> 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  <http://www.rasch.org/rmt/> www.rasch.org/rmt/ Latest RMT:
23:2 Autumn 2009


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