plotCI: Plotting confidence intervals and DIF

In david-ti/wrightmap: IRT Item-Person Map with 'ConQuest' Integration

Plotting confidence intervals and DIF

Description

The plotCI function is intended for graphing confidence intervals. The difplot function is a wrapper for plotCI specifcally intended for examining Differential Item Functioning from ConQuest output.

Usage

plotCI(ests, errors, labels = "", zeroline = TRUE, incol = "gray", outcol = "blue"
, main.title = "Statistical Significance Plot", axes = FALSE, xlab = "", pch = 16, ...)
## Default S3 method:
difplot(data, grouptype = NULL, group = NULL, item.names = NULL
, ylim = c(-1, 1), ylab = NULL, ...)
## S3 method for class 'CQmodel'
difplot(data, table.name = NULL, grouptype = NULL
, group = NULL, ...)
## S3 method for class 'character'
difplot(data, equation, ...)

Arguments

plotCI parameters:

ests	vector of point estimates.
errors	vector of standard errors.
labels	vector of labels for the items.
zeroline	logical indicating whether to draw a line at zero.
incol	color of intervals containing zero.
outcol	color of intervals not containing zero.
main.title	title of the plot.
axes,xlab,pch	parameters passed to plot.

difplot parameters:

data	A CQmodel object or the name of a ConQuest show file. Can also be a table of parameters taken from ConQuest output.
table.name	The RMP table to use for parameters. Should be an interactions table.
grouptype	The name of the demographic variable (e.g. “gender”).
group	The name of the group to test for DIF (e.g. “male”).
item.names	vector of item names.
equation	string specifying the model equation, if the Summary of Estimation table was not included in the show file.
ylim,ylab	more parameters passed to plot.
...	additional parameters to pass to plot.

Details

The plotCI function takes point estimates and standard errors as inputs and plots 95 percent confidence intervals in relation to a zero-line. By default, it colors the intervals gray if they include zero, and blue if they do not. The difplot function is a wrapper for plotCI specifcally intended for examining Differential Item Functioning from ConQuest output and expects tables formatted exactly like ConQuest output to work correctly. For plotting DIF from other statistical packages, it is recommended to use plotCI directly.

Author(s)

David Torres Irribarra and Rebecca Freund

Examples

	#Plotting confidence intervals
	
	ests <- rnorm(10,sd = .5)
	errors <- runif(10,min = .1,max = .5)
	plotCI(ests,errors,ylim = c(-3,3))
	
	#DIF plot:
	
	fpath <- system.file("extdata", package="WrightMap")

	# equation must be specified because there is no summary of estimation 
	# table in this example
	difplot(file.path(fpath,"ex6a.shw"), equation = "item-gender+item*gender") 

david-ti/wrightmap documentation built on May 24, 2022, 3:53 p.m.