plot.info {irtQ}

Plot Item and Test Information Functions

Description

This method function plots item or test information function given a specified theta values. In addition, it displays the conditional standard errors at a test level.

Usage

## S3 method for class 'info'
plot(
  x,
  item.loc = NULL,
  overlap = FALSE,
  csee = FALSE,
  xlab.text,
  ylab.text,
  main.text,
  lab.size = 15,
  main.size = 15,
  axis.size = 15,
  line.color,
  line.size = 1,
  layout.col = 4,
  strip.size = 12,
  ...
)

Arguments

x

x An object of class info.

item.loc

A vector of numeric values indicating that the item information functions of the nth items (or the location of items in a test form) are plotted. If NULL, the test information function for the total test form is drawn. Default is NULL.

overlap

Logical value indicating whether multiple item information functions are plotted in one panel. If FALSE, multiple item information functions are displayed in multiple panels, one for each.

csee

Logical value indicating whether the function displays the conditional standard error of estimation (CSEE) at a test level. If FALSE, item/test information function is plotted. Note that the CSEE plot is displayed only at a test level.

xlab.text, ylab.text

A title for the x and y axes.

main.text

An overall title for the plot.

lab.size

The size of xlab and ylab. Default is 15.

main.size

The size of main.text. Default is 15.

axis.size

The size of labels along the x and y axes. Default is 15.

line.color

A character string specifying a color for the line. See http://www.cookbook-r.com/Graphs/Colors_(ggplot2)/ for more details about colors used in ggplot2.

line.size

The size of lines. Default is 1.

layout.col

An integer value indicating the number of columns in the panel when displaying the item information functions of the multiple items. Default is 4.

strip.size

The size of facet labels when the item information functions of the multiple items are drawn.

...

Further arguments passed from the function geom_line() in the ggplot2 package.

Details

All of the plots are drawn using the ggplot2 package. The object of class info can be obtained from the function info.

Value

This method function displays the item or test information function plot. When csee = TRUE, the conditional standard error is returned at the test level.

Author(s)

Hwanggyu Lim [e-mail]

See Also

info

Examples

## the use of a "-prm.txt" file obtained from a flexMIRT
# import the "-prm.txt" output file from flexMIRT
flex_prm <- system.file("extdata", "flexmirt_sample-prm.txt", package = "irtQ")

# read item parameters and transform them to item metadata
test_flex <- bring.flexmirt(file=flex_prm, "par")$Group1$full_df

# set theta values
theta <- seq(-4, 4, 0.1)

# compute item and test information values given the theta values
x <- info(x=test_flex, theta=theta, D=1, tif=TRUE)

# draw a plot of the test information function
plot(x)

# draw a plot of the item information function for the second item
plot(x, item.loc=2)

# draw a plot of multiple item information functions across the multiple panels
plot(x, item.loc=1:8, overlap=FALSE)

# draw a plot of multiple item information functions in one panel
plot(x, item.loc=1:8, overlap=TRUE)

# draw a plot of conditional standard error at a test level
plot(x, csee=TRUE)