Of the three polytomous item IRT models PROC IRT claims to estimate, it appears that only one (the Graded Response Model) actually works. Recognizing that the procedure is still experimental, there seems no way to even specify the Generalized Partial Credit Model, contrary to information in the documentation. The Nominal Response Model provides some basic preliminary output, including a notice that the convergence criterion has been satisfied, and occasionally the following warning:   WARNING: Standard errors for some parameter estimates are close to zero.   However, fit statistics and parameter estimates are never produced.   Has this been your experience, too? ... View more

Is the Generalized Partial Credit really available in PROC IRT?     What’s New in SAS/STAT 14.1 states that  The generalized partial credit (GPC) model is available for ordinal items   The Response Models part of the Details section states that PROC IRT supports several response models for binary and ordinal responses, and it allows different items to have different response models. Details about these response models and their relationships follow: ... •Generalized partial credit model: This model assumes that items are ordinal-categorical with at most 19 levels. The slopes (or discrimination) and the step parameters of the items are free parameters in the model.   In addition, the EQUALITY subcommand includes the following possible specifications: ... _ALLGPC_ _ALLGPCITEM_ specifies all variables that are fitted by the generalized partial credit model in the analysis.  ... _ALLGPC_BUT_ [ excluded-variables ] _ALLGPCITEM_BUT_ [ excluded-variables ] specifies all variables except the excluded-variables that are fitted by the generalized partial credit model in the analysis.   However, a corresponding RESFUNC= option fof the model is not included in the syntax documentation for the MODEL subcommand. Are these all documenatation errors?               ... View more