Estimating Difficulty from Polytomous Categorical Data

A comprehensive analysis of difficulty for multiple-choice items requires information at different levels: the test, the items, and the alternatives. This paper introduces a new parameterization of the nominal categories model (NCM) for analyzing difficulty at these three levels. The new parameterization is referred to as the NE-NCM and is statistically equivalent to the NCM. The NE-NCM is applied to a sample of responses from a logical analysis test. The results suggest that the individuals execute a self-terminated response process that is mostly determined by working memory load.