Analysis of Empirical Data Using Two Logistic Latent Trait Models

Although Birnbaum's logistic models have been known since 1957, there have been few applications to empirical data reported in the literature. In this study, the one‐ and two‐parameter logistic models were compared with respect to their capacity to predict the distribution of statistics for estimating ability. The results of this study suggest that the two‐parameter model will provide greatest improvement over the one‐parameter model when applied to data from short tests where the variability of the discrimination parameters is substantial. Whether the gains are worth the increased cost of solving for the parameters of the more complex model is a question which requires investigation.