mixRasch (version 1.1)

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

Description

This function produces item characteristic curves for the family of Rasch models.

Usage

rICC(delt, theta, itemVector, xlim, ylim, plotTitle, xlab, ylab,  col = c("black","white"), colTheme, expectedScore=FALSE,  empICC=FALSE, empOnly=FALSE, gDevice, file, ...)

Arguments

delt

The threshold difficulties from a dichotomous or polytomous Rasch model.

theta

The estimated theta values associated with the analysis and paired with itemVector, only required when requesting an empirical ICC.

itemVector

The observed item responses, only required when requesting an empirical 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.

expectedScore

Flag indicating whether polytomous items are presented as category probabilities (FALSE) or expected item scores (TRUE). Will be set to TRUE when requesting empirical ICC.

empICC

Flag indicating whether an empirical ICC should also be produced.

empOnly

A flag indicating if ONLY the empirical ICC should be produced.

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.

Details

The function produces an item characterisic curce plots. Both empirical and theoretical ICCs can be produced.

Examples

library(mixRasch)
# Example data included with mixRasch
data(exRasch)

rasch1 <- mixRasch(exRasch,1,50, conv.crit=.0001, n.c=1)

# ICC for item 1
rICC(rasch1$item.par$delta[,1], rasch1$person.par$theta, 
     exRasch[,1], empICC=TRUE, colTheme="cavaliers")