AN UPPER ASYMPTOTE FOR THE THREE‐PARAMETER LOGISTIC ITEM‐RESPONSE MODEL*

Abstract

An upper‐asymptote parameter was added to the three‐parameter logistic item response model. This four‐parameter model was compared to the three‐parameter model on four data sets. The fourth parameter increased the likelihood in only two of the four sets. Ability estimates for the students were generally unchanged by the introduction of the fourth parameter.