CDM (version 8.2-6)

IRT.irfprob: S3 Methods for Extracting Item Response Functions

Description

This S3 method extracts item response functions evaluated at a grid of abilities (skills). Item response functions can be plotted using the IRT.irfprobPlot function.

Usage

IRT.irfprob(object, ...)
# S3 method for din
IRT.irfprob(object, ...)
# S3 method for gdina
IRT.irfprob(object, ...)
# S3 method for gdm
IRT.irfprob(object, ...)
# S3 method for mcdina
IRT.irfprob(object, ...)
# S3 method for reglca
IRT.irfprob(object, ...)
# S3 method for slca
IRT.irfprob(object, ...)

Value

An array with item response probabilities (items \(\times\)

categories \(\times\) skill classes [\(\times\) group]) and attributes

theta

Uni- or multidimensional skill space (theta grid in item response models).

prob.theta

Probability distribution of theta

skillspace

Design matrix and estimated parameters for skill space distribution (only for IRT.posterior.slca)

G

Number of groups

Arguments

object

Object of classes din, gdina, mcdina, gdm, slca, reglca.

...

More arguments to be passed.

See Also

Plot functions for item response curves: IRT.irfprobPlot.

For extracting the individual likelihood or posterior see IRT.likelihood or IRT.posterior.

Examples

if (FALSE) {
#############################################################################
# EXAMPLE 1: Extracting item response functions mcdina model
#############################################################################

data(data.cdm02, package="CDM")

dat <- data.cdm02$data
q.matrix <- data.cdm02$q.matrix

#-- estimate model
mod1 <- CDM::mcdina( dat, q.matrix=q.matrix)
#-- extract item response functions
prmod1 <- CDM::IRT.irfprob(mod1)
str(prmod1)
}