IRT.irfprob function

S3 Methods for Extracting Item Response Functions

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.

IRT.irfprob(object, ...)

## S3 method for class 'din'
IRT.irfprob(object, ...)

## S3 method for class 'gdina'
IRT.irfprob(object, ...)

## S3 method for class 'gdm'
IRT.irfprob(object, ...)

## S3 method for class 'mcdina'
IRT.irfprob(object, ...)

## S3 method for class 'reglca'
IRT.irfprob(object, ...)

## S3 method for class 'slca'
IRT.irfprob(object, ...)

Arguments

• object: Object of classes din, gdina, mcdina, gdm, slca, reglca.
• ...: More arguments to be passed.

Returns

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

See Also

Plot functions for item response curves: IRT.irfprobPlot.

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

Examples

## Not run:

#############################################################################
# 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)
## End(Not run)