This function estimates conditional covariances of itempairs (Stout, Habing, Douglas & Kim, 1996; Zhang & Stout, 1999a). The function is used for the estimation of the DETECT index.
ccov.np(data, score, bwscale=1.1, thetagrid=seq(-3, 3, len=200),
progress=TRUE, scale_score=TRUE)An \(N \times I\) data frame of dichotomous responses. Missing responses are allowed.
An ability estimate, e.g. the WLE
Bandwidth factor for calculation of conditional covariance. The bandwidth
used in the estimation is bwscale times \(N^{-1/5}\).
A vector which contains theta values where conditional covariances are evaluated.
Display progress?
Logical indicating whether score
should be z standardized in advance of the calculation of
conditional covariances
Stout, W., Habing, B., Douglas, J., & Kim, H. R. (1996). Conditional covariance-based nonparametric multidimensionality assessment. Applied Psychological Measurement, 20, 331-354.
Zhang, J., & Stout, W. (1999). Conditional covariance structure of generalized compensatory multidimensional items, Psychometrika, 64, 129-152.