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Title: Equating tests with mixed format tests Authors:  Marie Wiberg - Umeå University (Sweden) [presenting]
Abstract: An achievement test typically contains items with different scoring formats, such as dichotomously scored and polytomously scored items. The aim is to propose a novel approach to equate achievement tests containing dichotomously scored and polytomously scored items. Previous research has focused on item response theory (IRT), observed-score equating, IRT true-score equating, frequency estimation and chain equating. We present a novel approach which can be used to equate two test versions which have a mixed item format. We focus on the equivalent group design and illustrate the method with real test data from a national test in mathematics. We also examined different conditions in a simulation study, including proportions of binary and polytomous items and when a different level of ability is seen in the groups which receive the different test versions. The proposed approach shows stable equating results and appears to be a good alternative to commonly used equating methods for mixed item format.