Generalized Graded Unfolding Model

An implementation of the generalized graded unfolding model (GGUM) in R, see Roberts, Donoghue, and Laughlin (2000) ). It allows to simulate data sets based on the GGUM. It fits the GGUM and the GUM, and it retrieves item and person parameter estimates. Several plotting functions are available (item and test information functions; item and test characteristic curves; item category response curves). Additionally, there are some functions that facilitate the communication between R and 'GGUM2004'. Finally, a model-fit checking utility, MODFIT(), is also available.

GGUM

The GGUM package fits the generalized graded response model (GGUM; Roberts et al., 1996, 2000). It is based on marginal maximum likelihood (Roberts et al., 2000) to estimate the item parameters and an estimated a posteriori (EAP) method to estimate the person parameters.

This package produces comparable results to the ones based on the GGUM2004 program (Roberts et al., 2000; Roberts et al., 2006), for the GUM (Model 3 in GGUM2004) and the GGUM (Model 8 in GGUM2004). For those accustomed to using GGUM2004, this packages provides a useful set of functions that allow exporting data and code to GGUM2004, running GGUM2004, and retrieving the parameter estimates. Thus, if desired, one can run GGUM2004 and retrieve the results completely from within the R environment.