Test equating under the multiple-choice model. Paper presented at the annual meeting of American Educational Research Association

This article presents a characteristic curve procedure for computing transformations of the item response theory (IRT) ability scale assuming the multiple-choice model. The multiple-choice model provides a realistic and informative approach to analyzing multiple-choice items in two impor-tant ways. First, the probability of guessing is a decreasing function of proficiency rather than a constant across different proficiency levels as in the three-parameter logistic model. Second, the model utilizes information from incorrect answers as well as from correct answers. The multiple-choice model includes many well-known IRT models as special cases, such as Bock’s nominal response model. Formulas needed to implement a characteristic curv