[Rasch] Help with equating partial credit items in pre - post test

Mike Linacre (RMT) rmt at rasch.org
Mon Jun 2 16:35:35 EST 2008


Thank you for your message, Steve.

You wrote: Mike. If there is a different unit, in principle the responses 
in frames of reference that have different units (due to different levels 
of discrimination) need to be modelled separately first then brought onto a 
common scale.

Reply: Agreed! If the NASA experts organizing the Mars Climate Orbiter had 
realized they had a "different unit" problem (meters and feet), it wouldn't 
have crashed!

The solution is called "Fahrenheit-Celsius" equating in the Rasch 
literature. It can be encountered when different item types (MCQ, 
T-F,  polytomies) are included in the same instrument. Or when the same 
instrument is given in different situations, e.g., high-stakes and low-stakes.

Cordially,
Mike L.

At 6/2/2008, you wrote:
>Mike. If there is a different unit, in principle the responses in frames 
>of reference that have different units (due to different levels of 
>discrimination) need to be modelled separately first then brought onto a 
>common scale. Higher discrimination produces responses for which the 
>Guttman pattern is more likely, other things being equal. I've shown cases 
>in which differences in the levels of discrimination produce very 
>misleading inferences in empirical situations if they are not dealt with 
>appropriately.

Mike Linacre
Editor, Rasch Measurement Transactions
rmt at rasch.org www.rasch.org/rmt/ Latest RMT:  21:4 Spring 2008
-------------- next part --------------
An HTML attachment was scrubbed...
URL: https://mailinglist.acer.edu.au/pipermail/rasch/attachments/20080602/4d750c70/attachment.html 


More information about the Rasch mailing list