Person Fit
Several person-fit statistics
(PFSs; Meijer and Sijtsma, 2001, )
are offered. These statistics allow assessing whether
individual response patterns to tests or questionnaires are (im)plausible given
the other respondents in the sample or given a specified item response theory model. Some PFSs apply to
dichotomous data, such as the likelihood-based PFSs (lz, lz*) and the group-based PFSs
(personal biserial correlation, caution index, (normed) number of Guttman errors,
agreement/disagreement/dependability statistics, U3, ZU3, NCI, Ht). PFSs suitable to polytomous data include
extensions of lz, U3, and (normed) number of Guttman errors.