plot.ddfMLR: ICC plots for an object of `"ddfMLR"` class.

Description

Plot method for an object of "ddfMLR" class using ggplot2.

The characteristic curves for an item specified in item argument are plotted. Plotted curves represent the best model.

Usage

# S3 method for ddfMLR
plot(x, item = "all", group.names, ...)

Value

Returns list of objects of class "ggplot".

Arguments

x: an object of "ddfMLR" class.
item: numeric or character: either character "all" to apply for all items (default), or a vector of item names (column names of Data), or item identifiers (integers specifying the column number).
group.names: character: names of reference and focal group.
...: other generic parameters for plot() function.

Author

Adela Hladka (nee Drabinova)
Institute of Computer Science of the Czech Academy of Sciences
Faculty of Mathematics and Physics, Charles University
hladka@cs.cas.cz

Patricia Martinkova
Institute of Computer Science of the Czech Academy of Sciences
martinkova@cs.cas.cz

Examples

Run this code

if (FALSE) {
# loading data
data(GMATtest, GMATkey)
Data <- GMATtest[, 1:20] # items
group <- GMATtest[, "group"] # group membership variable
key <- GMATkey # correct answers

# testing both DDF effects
(x <- ddfMLR(Data, group, focal.name = 1, key))

# graphical devices
plot(x, item = "Item1", group.names = c("Group 1", "Group 2"))
plot(x, item = x$DDFitems)
plot(x, item = c(3, 1, 5))
}