[Rasch] Rating scale and partial credit model with identical responses

Mike Linacre rmt at rasch.org
Mon Jun 26 23:13:36 EST 2006


Dear Rama:

Thank you for your question - it addresses an important issue in 
statistical analysis.

These "perfect" response strings are a problem for any type of analysis! 
These response strings are like putting each student's MCQ bubble sheet 
through an optical scanner 5 times, and then thinking that you had 5 
observations of each student's responses to each item.

If you really have a dataset like this, then 4 of the 5 judges are 
redundant, and their data should be eliminated. It provides no extra 
statistical information.

You would then have only one statistically-independent observation of each 
student. This is enough to order the students, but not enough to construct 
a verifiably linear measurement system.

OK?

Mike L.

At 6/26/2006, you wrote:

>Dear all,
>If  on a set of polytomous items or Likert scale items students get the
>same score on each individual item, is it a problem for Rasch analysis?
>Suppose, the response vectors for 5 polytomous items for 5 respondents
>are:
>44444
>33333
>55555
>11111
>44444
>And this pattern continues for all respondents.
>This could well be the case when there is complete agreement among
>judges in rated performances, which could be the result of good training
>and the existence of a well defined rating scale.
>Thanks
>Rama
>
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Mike Linacre, mike at winsteps.com
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