A cautionary note on IRT-based linking of tests with polytomous items

Published discussions of the year-to-year linking of tests comprised of pol ytomous items appear to suggest that the linking logic traditionally used f or multiple-choice items is also appropriate for polytomous items. It is ar gued and illustrated that a modification of the traditional linking is nece ssary when tests consist of constructed-response items judged by raters and there is a possibility of year-to-year variation in the rating discriminat ion and severity.