Many researchers have suggested that the main cause of item bias is the misspecification of the latent ability space. That is, items that measure multiple abilities are scored as though they are measuring a single ability. If two different groups of examinees have different underlying multidimensional ability distributions and the test items are…

A two-dimensional, compensatory item response model and a unidimensional model were fitted to the reading and mathematics items in the Woodcock-Johnson Psycho-Educational Battery-Revised for a sample of 1,000 adults aged 20-39 years. Multidimensional information theory predicts that if the unidimensional abilities can be represented as vectors in…