[Rasch] CAT Questions

Svend Kreiner S.Kreiner at biostat.ku.dk
Fri Jan 29 02:36:45 EST 2010


Dear Ranganath,

You use IRT models to test that your measurements are valid and you use 
Rasch models to test that measurement is valid */and/* objective. And, 
of course, to be able to calculate (estimate) measures on the proper 
underlying latent trait scale.

Under the Rasch model, some would argue that you do not need to 
calculate the person estimates since the raw score is sufficient. During 
computer adaptive testing this cannot be avoided even with the Rasch 
since you want to compare scoeres from different subsets of items. In 
these situations there is no way around IRT models and Rasch models are 
for several reasons (methodological and technical) the best model for 
that purpose.

Best regards

Svend

ranganaths skrev:
>
> Hi,
>
>  
>
>      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.
>
>  
>
> Regards,
>
> Ranganath S
>
>  
>
> ------------------------------------------------------------------------
>
> *From:* Mike Linacre (RMT) [mailto:rmt at rasch.org]
> *Sent:* Thursday, January 28, 2010 10:41 AM
> *To:* rasch at acer.edu.au
> *Subject:* Re: [Rasch] CAT Questions
>
>  
>
> Thank you for asking us, Ranganaths.
>
> You asked:
>
> 1. I am wondering how the IRT in its computer application version 
> called CAT useful in accessing a student?.
>
>
> Answer: CAT is useful and effective. Each student can have a 
> customized test with increased security and flexible test scheduling. 
> relative to paper-and-pencil tests.
>
> You asked:
>
> 2. What question types are used for CAT?
>
>
> Reply: Any type that can be computer-scored. Multiple-choice questions 
> are the most common.
>
> You asked:
>
> 3. Which of the 3 models 1P, 2P and 3P is useful for a correct 
> judgment of the students ability?
>
>
> Reply: In practice, 1P (Rasch) is the most practical model for item 
> selection and ability estimation for items scored right/wrong.
>
> You asked:
>
> 4. Which book is best suited to know the advanced form of IRT for the 
> real application of it?
>
>
> Reply: You could start with a Google search of www.rasch.org 
> <http://www.rasch.org/> for documents explaining basic CAT concepts. 
> Then Google-search the Internet for documents and books relating to 
> more complex topics, such as CAT test security and CAT item exposure.
>
> OK?
> Mike L.
>
> Mike Linacre
> Editor, Rasch Measurement Transactions
> rmt at rasch.org www.rasch.org/rmt/ <http://www.rasch.org/rmt/> Latest 
> RMT:  23:2 Autumn 2009
>
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> ------------------------------------------------------------------------
>
> _______________________________________________
> Rasch mailing list
> Rasch at acer.edu.au
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>   

-- 
Svend Kreiner
Professor
Department of Biostatistics  
University of Copenhagen 

Øster farimagsgade 5, entr. B
P.O. Box 2099
DK-1014 Copenhagen K, Denmark

Email: S.Kreiner at biostat.ku.dk
Phone: (+45) 35 32 75 97     

Fax: (+45) 35 32 79 07


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