irtoys (version 0.1.4)

plot.iif: A plot method for item information functions

Description

Useful for plotting item information functions. The x argument of iif should better be left out unless something special is required.

Usage

## S3 method for class 'iif':
plot(x, add = FALSE, main = "Item information function", 
  co = 1, label = FALSE, ...)

Arguments

x

An object produced by function iif

add

When add=T, the IIF is added to a plot, otherwise a new plot is started. Default is F.

main

The main title of the plot, given that add=F.

co

The colour of the IIF curve. Default is 1 for black. Use co=NA to plot each IIF in a different colour.

label

When label=T, individual curves will be labeled with the item number.

...

Any additional plotting parameters

See Also

iif

Examples

data(Scored)
p.2pl  <- est(Scored, model="2PL", engine="ltm")
# plot IIF for all items in red, label with item number
plot(iif(p.2pl), co="red", label=TRUE)
# plot IIF for items 2, 3, and 7 in different colours
plot(iif(p.2pl[c(2,3,7),]), co=NA)