Item Parameter Recovery for the Nominal Response Model.

This study extended item parameter recovery studies in item response theory to the nominal response model (NRM). The NRM may be used with computerized adaptive testing, testlets, demographic items, and items whose alternatives provide educational diagnostic information. Moreover, with the increasing popularity of performance-based assessment, the use of polytomous item response theory models, in general, and the NRM in particular, will more than likely see increased application. Establishing guidelines for reasonable item parameter estimation was seen as fundamental to the use of the NRM. Factors studied through simulation were the sample size ratio, the latent ability distribution, and item information level. Results showed that as the latent ability distribution departs from a uniform distribution the accuracy of estimating the slope parameter decreased. This decrease in accuracy may be compensated for, in part, by increasing the sample size. Moreover, more informative items tended not to be as well estimated as less informative items. The results appear to indicate that if one is interested in estimating ability, a sample size ratio of 5:1 can produce reasonably accurate item parameter estimates for this purpose. (Contains 7 figures, 7 tables, and 26 references.) (Author/SLD)