[Rasch] Item anchoring/unanchoring in CAT

Mike Linacre mike at winsteps.com
Thu Mar 21 09:48:46 EST 2013

Patrick, in case no one has answered ...

When a CAT test is administered, we require every item to be anchored. 
Unanchored items are not informative about the respondent's ability level.

When recalibrating the item bank, items that have large displacements 
have their anchored difficulty values updated. For convenience, the 
updated item can be banked as a new item. The original item maintains 
its old difficulty for retrospective analyses, but is removed from the 
active CAT bank.


Mike L.

On 3/19/2013 11:09 AM, Patrick B. Fisher wrote:
> In working with CAT items (Computerized Adaptive Testing), I'm curious 
> about anchoring vs. unanchoring items that have displaced 
> significantly. Why are items not unanchored to let float on the scale 
> in CAT?

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