plot.tam: Plot Function for Unidimensional Item Response Models

View source: R/plot.tam.R

plot.tamR Documentation

Plot Function for Unidimensional Item Response Models

Description

S3 plot method for objects of class tam, tam.mml or tam.mml.

Usage

## S3 method for class 'tam'
plot(x, items=1:x$nitems, type="expected", low=-3, high=3, ngroups=6,
                   groups_by_item=FALSE, wle=NULL, export=TRUE, export.type="png",
                   export.args=list(), observed=TRUE, overlay=FALSE,
                   ask=FALSE, package="lattice", fix.devices=TRUE, nnodes=100, ...)

## S3 method for class 'tam.mml'
plot(x, items=1:x$nitems, type="expected", low=-3, high=3, ngroups=6,
                       groups_by_item=FALSE, wle=NULL, export=TRUE, export.type="png",
                       export.args=list(), observed=TRUE, overlay=FALSE,
                       ask=FALSE,  package="lattice",  fix.devices=TRUE, nnodes=100, ...)

## S3 method for class 'tam.jml'
plot(x, items=1:x$nitems, type="expected", low=-3, high=3, ngroups=6,
                       groups_by_item=FALSE, wle=NULL, export=TRUE, export.type="png",
                       export.args=list(), observed=TRUE, overlay=FALSE,
                       ask=FALSE,  package="lattice", fix.devices=TRUE, nnodes=100, ...)

Arguments

x

Object of class tam, tam.mml or tam.mml.

items

An index vector giving the items to be visualized.

type

Plot type. type="expected" plot the expected item response curves while type="items" plots the response curves of all item categories.

low

Lowest θ value to be displayed

high

Highest θ value to be displayed

ngroups

Number of score groups to be displayed. The default are six groups.

groups_by_item

Logical indicating whether grouping of persons should be conducted item-wise. The groupings will differ from item to item in case of missing item responses.

wle

Use WLE estimate for displaying observed scores.

export

A logical which indicates whether all graphics should be separately exported in files of type export.type in a subdirectory 'Plots' of the working directory.

export.type

A string which indicates the type of the graphics export. For currently supported file types, see grDevices::dev.new.

export.args

A list of arguments that are passed to the export method can be specified. See the respective export device method for supported usage.

observed

A logical which indicates whether observed response curve should be displayed

overlay

A logical indicating whether expected score functions should overlay.

ask

A logical which asks for changing the graphic from item to item. The default is FALSE.

package

Used R package for plot. Can be "lattice" or "graphics".

fix.devices

Optional logical indicating whether old graphics devices should be saved.

nnodes

Number of θ points at which item response functions are evaluated

...

Further arguments to be passed

Details

This plot method does not work for multidimensional item response models.

Value

A plot and list of computed values for plot (if saved as an object)

Author(s)

Margaret Wu, Thomas Kiefer, Alexander Robitzsch, Michal Modzelewski

See Also

See CDM::IRT.irfprobPlot for a general plot method.

Examples

## Not run: 
#############################################################################
# EXAMPLE 1: Dichotomous data data.sim.rasch
#############################################################################

data(data.sim.rasch)
mod <- TAM::tam.mml(data.sim.rasch)
# expected response curves
plot(mod, items=1:5, export=FALSE)
# export computed values
out <- plot(mod, items=1:5, export=FALSE)
# item response curves
plot(mod, items=1:5, type="items", export=FALSE)
# plot with graphics package
plot(mod, items=1:5, type="items", export=FALSE, ask=TRUE, package="graphics")

#############################################################################
# EXAMPLE 2: Polytomous data
#############################################################################

data(data.Students, package="CDM")
dat <- data.Students[, c("sc3","sc4", "mj1", "mj2" )]
dat <- na.omit(dat)
dat[ dat[,1]==3, 1 ] <- 2   # modify data
dat[ 1:20, 2 ] <- 4

# estimate model
mod1 <- TAM::tam.mml( dat )
# plot item response curves and expected response curves
plot(mod1, type="items", export=FALSE)
plot(mod1, type="expected", export=FALSE )

## End(Not run)

TAM documentation built on May 15, 2022, 1:05 a.m.