irtoys (version 0.1.4)

plot.irf: A plot method for item response functions

Description

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

Usage

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

Arguments

x

An object produced by function irf

add

When add=T, the IRF 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 IRF curve. Default is 1 for black. Use co=NA to plot each IRF in a different colour.

label

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

...

Any additional plotting parameters

See Also

irf

Examples

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