An application of the three-parameter IRT model to vertical equating

Abstract

This study examined the effectiveness of the three-parameter IRT model in vertically equating five overlapping levels of a mathematics computation test. One to four test levels were administered within intact classrooms to randomly equivalent groups of third through eighth grade students. Test characteristic curves were derived for each grade/test level combination. It was generally found that an examinee would receive a higher ability estimate if the test level administered had been calibrated on less able examinees. Practical implications for "out-of-level" and adaptive testing are discussed.