rpf (version 0.7)

An introduction: rpf - Response Probability Functions

Description

The purpose of this package is to factor out logic and math common to Item Response Theory fitting, diagnostics, and analysis. It is envisioned as core support code suitable for more specialized IRT packages to build upon.

Warning

The API is not stable at this time. You have been warned. In particular, I anticipating transposing some of the input and output matrices.

Details

This package provides optimized, low-level functions to map parameters to response probabilities for dichotomous (1PL, 2PL and 3PL) rpf.drm and polytomous (graded response rpf.grm, partial credit/generalized partial credit rpf.gpcm, nominal rpf.nrm, and multiple-choice model rpf.mcm) items. Both unidimensional and multidimensional versions of the models are available.

Item model parameters are passed around as a numeric vector. A 1D matrix is also acceptable. Regardless of model, parameters are always ordered as follows: discrimination ("a"), difficulty ("b"), and guessing ("c").

This package could also accrete functions to support plotting (but not the actual plot functions).

References

Thissen, D. and Steinberg, L. (1986). A taxonomy of item response models. Psychometrika 51(4), 567-577.

See Also

See rpf.rparam to create item parameters.