A minimum X² method for equating tests under the graded response model

Abstract

The minimum X² method for computing equating coefficients for tests with dichotomously scored items was extended to the case of Samejima’s graded response items. The minimum X² method was compared with the test response function method (also referred to as the test characteristic curve method) in which the equating coefficients were obtained by matching the test response functions of the two tests. The minimum X² method was much less demanding computationally and yielded equating coefficients that differed little from those obtained using the test response function approach. Index terms: equating, graded response model, item response theory, minimum X² method, test response function method.