Selection of Unidimensional Scales From a Multidimensional Item Bank in the Polytomous Mokken I RT Model

An automated item selection procedure for selecting unidimensional scales of polytomous items from multi dimensional datasets is developed for use in the context of the Mokken item response theory model of monotone homogeneity (Mokken Molenaar, 1991). New theoretical results relating the latent model structure to H are provided. The item selec tion procedure requires selection of a lower bound for H. A simulation study determined ranges of H for which the unidimensional item sets were retrieved from multidimensional datasets. If multidimensionality is suspected in an empirical dataset, well-chosen lower bound values can be used effectively to detect the unidi mensional scales.