[Rasch] Item weighting for polytomies

Mike Linacre (RMT) rmt at rasch.org
Fri Apr 30 14:17:20 EST 2010

Thank you for your questions, Gao.

The Rasch measures are based on the raw scores. Since the raw score range 
for a 0,1,2,3,4,5 polytomous item is 5 times the raw score range for a 0,1 
dichotomous item, the polytomous item is automatically weighted 5 times 
more than the dichotomous item. Only weight the items if you do not want 
the polytomous item to have 5 times the weight of the dichotomous item.


Mike L.

At 4/30/2010, you wrote:
>now i have a question about the item weighting issue. If the 
>polychotomousy socred items are set by  ISGROUP=. Say, they are have 
>different score value from the dichotomously scored items.  is it 
>necessary to set the IWEIGHT value according to their raw scores?
>For instance, if the possible response scores for one item are 
>0,1,2,3,4,5, then the weighting of that item is 5,yes?

Mike Linacre
Editor, Rasch Measurement Transactions
rmt at rasch.org www.rasch.org/rmt/ Latest RMT:  23:4 Spring 2010
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