[Rasch] Raw score mean and classical item difficulty
luckyantonio2003 at yahoo.com
Thu Dec 8 21:55:29 EST 2011
There are two tests each having 25 items. Each test is taken by 50 persons.
The mean of classical item difficulties for the two tests (computed within their group) is almost the same (.61 &. 58).
The raw score mean of the two groups are different by one point (21 & 22 ).
Can these data be real?
Is it possible for two groups to have almost the same mean proportion of correctly answering the items (item difficulty) but be different in means by one point out of a maximum of 25?
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