CDM (version 4.8-0)

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 class 'din':
IRT.irfprob(object, \dots)

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

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

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

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

Arguments

object

Object of classes din, gdina, mcdina, gdm or

...

More arguments to be passed.

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

See Also

Plot functions for item response curves: IRT.irfprobPlot. For extracting the individual likelihood or posterior see IRT.likelihood or IRT.posterior.

Examples

#############################################################################
# EXAMPLE 1: Extracting item response functions mcdina model
#############################################################################

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

# estimate model (only 5 iterations for illustration purposes)
mod1 <- mcdina( dat , q.matrix=q.matrix , maxit = 5)
# extract item response functions
prmod1 <- IRT.irfprob(mod1)
str(prmod1)