CTT (version 2.3.4)

cttICC: Function for producing theoretical and empirical item characteristic curves.

Description

This function produces empirical item characteristic curves.

Usage

cttICC(scores, itemVector, xlim, ylim, plotTitle, xlab, ylab, 
     col = c("black","white"), colTheme, gDevice, file, ...)

Arguments

scores

A total measure score, for creating expected mean values of the item.

itemVector

Observed item responses for the item ICC.

xlim

A vector overriding default limits for the x axis.

ylim

A vector overriding default limits for the y axis.

plotTitle

Controls the main plot title.

xlab

The label for the x axis.

ylab

The label for the y axis.

col

A vector of the colors to be used in the plot. The first color will be used for item labels. The second color will be used for shading the area of rejection.

colTheme

Four color themes ("cavaliers", "dukes", "spartans", "greys") are provided. If you provide a color theme, it will override the col paramater.

gDevice

Controls graphics device. Options are "screen" (default), "jpg", or "png".

file

The name of the output file if a device other than "screen" is chosen.

...

Additional parameters passed to the plot command.

Author

John T. Willse

Details

The function produces an item characterisic curve plot. The empirical ICC is created by calculating the item mean in between 2 and 20 bins. There must be at least 15 observations per bin, or a smaller number of bins is used.

Examples

library(CTT)# Example data provided with package
data(CTTdata)
data(CTTkey)

# Scores for each preson 
myScores <- score(CTTdata,CTTkey, output.scored=TRUE)

# ICC for item 1
cttICC(myScores$score, myScores$scored[,1], colTheme="spartans", cex=1.5)