Effect of examinee group on equating relationships

Abstract

Many educational tests make use of multiple test forms, which are then horizontally equated to establish interchangeability among forms. To have confidence in this interchangeability, the equating relationships should be robust to the particular group of examinees on which the equating is conducted. This study investigated the effects of ability of the examinee group used to establish the equating relationship on linear, equipercentile, and three-parameter logistic IRT estimated true score equating methods. The results show all of the methods to be reasonably independent of examinee group, and suggest that population independence is not a good reason for selecting one method over another.