Published online by Cambridge University Press: 01 January 2025
The purpose of this note is to focus on the finiteness of the weighted likelihood estimator (WLE) of ability in the context of dichotomous and polytomous item response theory (IRT) models. It is established that the WLE always returns finite ability estimates. This general result is valid for dichotomous (one-, two-, three- and four-parameter logistic) IRT models, the class of polytomous difference models and divide-by-total models, independently of the number of items, the item parameters and the response patterns. Further implications of this result are outlined.
Electronic supplementary material The online version of this article (doi:10.1007/s11336-016-9518-9) contains supplementary material, which is available to authorized users.