Analysis of items and persons in data. To identify and remove person misfit in polytomous
item-response data using either 'mokken' or a graded response model (GRM, via 'mirt').
Provides automatic thresholds, visual diagnostics (2D/3D), and export utilities.
Methods build on Mokken scaling as in Mokken (1971, ISBN:9789027968821) and on the
graded response model of Samejima (1969)