Item-Weighted Likelihood Method for Ability Estimation in Tests Composed of Both Dichotomous and Polytomous Items

For mixed-type tests composed of both dichotomous and polytomous items, polytomous items often yield more information than dichotomous ones. To reflect the difference between the two types of items, polytomous items are usually pre-assigned with larger weights. We propose an item-weighted likelihood method to better assess examinees' ability levels. Simulation results show that the estimated ability based on the new procedure is more consistent with examinee’s true ability than the usual maximum likelihood method.