[Rasch] tresholds

Muy Ignoto ignoto.999 at hotmail.com
Fri Jul 6 23:11:53 EST 2007

Hello to all:
I'm new to the list, and also new to Rasch models. I've read many books, bu I still have some doubts. I hope you could help me with them.
I undertand that in polytomous items, there are two kind of tresholds: Rasch-thurstone: whic are allways ordered, and are the intersection of the probability to have for example 0 vs 1 point, 1 vs 2 points, 2 vs 3 ponts and so on) and the Rasch-Andrich that are the probability to observe each catebory conditional on the person measure.
My quesion is: Do we need to colapse the categories if the treshold are disordered? or it depends, for example, if the mean hability por the persons selecing each score point is ordered, but the treshold are disordered it is ok, and I don't need to colapse the categories?
Thank you
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