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The items from tests from two content areas, information literacy and global issues, were examined for item parameter drift across four years. The items on the information literacy test were expected to show more drift because the content of this field is changing more rapidly and because the test changed from low to high stakes for students while the other test remained low stakes. More items did show drift on the information literacy test, but the drift was not always readily explained. Further, some items did not fit the drift model available in BILOG-MG, either because the drift was a one-time shift rather than a gradual change or because both the discrimination and difficulty changed over time.
DeMars, C. E. (2004, April). Item parameter drift: The impact of the curricular area. Paper presented at the annual meeting of the American Educational Research Association, San Diego.