rpf.ot2000.chisq1: Compute S-Chi-squared fit statistic for 1 item
Description
Implements the Kang & Chen (2007) polytomous extension to
S-Chi-squared statistic of Orlando & Thissen (2000). Fails
in the presence of missing data.Usage
rpf.ot2000.chisq1(spec, param, free, item, observed, quad = NULL)
Arguments
spec
a list of item specifications
free
a matrix of the same shape as param
indicating whether the parameter is free (TRUE) or fixed
observed
a matrix of observed raw scores by the
outcome of the item of interest
quad
the quadrature rule (default is equally
spaced intervals with 49 points)
Details
NOTE: IRTPRO 2.1 uses an equal interval quadrature rule by
default.WARNING: The algorithm for collapsing low-count cells has
not been tested thoroughly.
References
Kang, T. and Chen, T. T. (2007). An investigation of the
performance of the generalized S-Chisq item-fit index for
polytomous IRT models. ACT Research Report Series.Orlando, M. and Thissen, D. (2000). Likelihood-Based
Item-Fit Indices for Dichotomous Item Response Theory
Models. Applied Psychological Measurement, 24(1),
50-64.