[Rasch] A practical one

John Barnard (EPEC) JohnBarnard at bigpond.com
Mon Oct 10 14:12:37 EST 2005


Thanks for your reply Trevor. Of course we would expect (at least hope
for) improvement in students' performance over time. However, think of
this as a test for say pilots to qualify (just for argument's sake). It
is thus a type of selection test rather than a "scholastic achievement"
test where one would expect some growth. (It is thus rather a qualifying
test and I know one can reason that those who failed could have put in
an extra effort this time.) The hypothesis is that the repeat group was
unfairly advantaged (competing for the same places) because they have
seen the items before. Through what I have done so far, this seems to be
the case. But now I want to account for this, i.e. trying to be fair to
those who have not seen the items before.

If this was not the case (and there was no additional effort) one would
expect the repeat group to have approx the same mean ability (if same
item difficulty estimates are used) in the two sessions. But, the mean
ability of the repeat group increased significantly.

Hope this clarifies the issue a little.

Kindly
John

John J Barnard
Executive Director: EPEC Pty Ltd
www.users.bigpond.com/JohnBarnard/

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-----Original Message-----
From: Trevor Bond [mailto:trevor.bond at jcu.edu.au] 
Sent: Monday, 10 October 2005 1:45 PM
To: John Barnard (EPEC); Rasch list
Subject: Re: [Rasch] A practical one


Dear John

Perhaps we (or, I, at least) need some more information to understand 
your problem. Kids who repeated an exam (after doing make up work or 
just remembering) score better on a test the second time round. They 
scored more correct responses at T2 than at T1. This seems to be 
exactly what I would expect . . .or hope for . . .as an educator. 
Clearly I have missed the nature of your 'problem'.
collegially
Trevor

At 1:32 PM +1000 10/10/05, John Barnard (EPEC) wrote:
>Dear all
>
>I would appreciate some opinions on the following scenario.
>
>The same paper was given on two occasions. Some 20% of students (let's 
>call them the repeaters) who sat the first round (and failed) also sat 
>the second round. In round 1, the repeaters' mean ability is (say) 0.5 
>logits less than the non-repeaters'. After anchoring the item 
>difficulties in the first round and using them in round 2 resulted in 
>the repeaters now doing significantly better (say 0.7 logits on 
>average). Also the repeaters now have approx the same mean ability as 
>the non-repeaters in round 2, say 0.8 logits.
>
>The question is this: If the repeaters' mean ability increased by 0.7 
>logits, how can one account for this (taking the same paper again) to 
>not unfairly advantage the repeat group in round 2? (I am aware of 
>learning and other factors, but let's ignore that for the moment.)
>
>Kindly
>John
>
>John J Barnard
>Executive Director: EPEC Pty Ltd www.users.bigpond.com/JohnBarnard/
>
>DISCLAIMER:
>The contents of this e-mail which may include one or more attachments, 
>is confidential and is intended for the use of the named recipient(s). 
>If you have received this e-mail in error, you are not permitted to and

>must not disclose, distribute or retain it, and are requested to notify

>the sender by return e-mail and delete it thereafter.
>
>It is the responsibility of the recipient(s) to ensure that the e-mail 
>is virus free. Although EPEC uses the latest antiviral software, we do 
>not accept responsibility for any problems caused by viruses.
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>
>
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-- 
Trevor G BOND Ph D
Professor and Head of Dept
Educational Psychology, Counselling & Learning Needs
D2-2F-01A EPCL Dept.
Hong Kong Institute of Education
10 Lo Ping Rd, Tai Po
New Territories HONG KONG

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