ppPlot: Person probability plots

Description

Plots a Wright Map for a single person (similar to a kidmap). On the person side, highlights their estimated ability and a range of one standard error. On the item side, draws lines representing item difficulties at which they are expected to have a 20%, 40%, 50%, 60%, and 80% chance of success.

Usage

ppPlot(thetas, thresholds, est, SE, main.title = "Person Probability Plot"
, cut.left = 0, cut.right = .94, cut.lab.adj = c(1,.5),...)
cutLines(cutpoints = NULL,cut.left = 0, cut.right = 1, cut.lab.text = NULL
, cut.lab.adj = c(0,1),...)

Arguments

thetas: a vector, matrix or data frame of person parameter estimates. Can also be a character string specifying a ConQuest output file of person parameter estimates, or a CQmodel object. Will be sent to the function personData.
thresholds: matrix or data frame of item parameter estimates. Can also be a character string specifying a ConQuest show file. Will be sent to the function itemData.
est: estimated ability of the person
SE: standard error of the estimate
main.title: title of the Person Probability Plot.
cut.left: value between 0 and 1 describing where to place the lefthand side of the cutpoints, as a fraction of the item plot.
cut.right: value between 0 and 1 describing where to place the righthand side of the cutpoints, as a fraction of the item plot.
cut.lab.adj: similar to the adj parameter in text, describes where to place the text for the cutpoints as a pair of values between 0 and 1 in terms of left-right and up-down alignment. Left-right alignment is 0 for the left side of the item plot and 1 for the right side, while up-down alignment is 0 for below the line and 1 for above the line.
cutpoints: argument to cutLines when called through wrightMap or one of the item.side functions. Specifies locations of cutlines. When cutLines is called through ppPlot, the cutpoints are calculated rather than specified.
cut.lab.text: argument to cutLines when called through wrightMap or one of the item.side functions. Specifies text to appear for each cut line. When cutLines is called through ppPlot, the text is always the percent chance of success given the estimated ability level and difficulty location.
...: additional arguments to pass to wrightMap or its associated functions.

Author

David Torres Irribarra and Rebecca Freund

Details

The ppPlot function is a wrapper for wrightMap that is specifically designed for person probability plots, and as such has access to all the parameters of wrightMap and its associated functions. It uses the person.points, person.range, p.point.col, and p.range.col parameters on the person.side function to draw a range of one standard error around the estimated ability level. On the item side, it calculates at what item difficulty the respondent is expected to have a 20%, 40%, 50%, 60%, and 80% chance of success and then uses the cutLines function to illustrate these cutpoints. The cutLines function should not be called on its own and may be hidden in future versions. It is included here to show the available parameters, which can be included in a call to wrightMap or any of the item.side functions.

Examples

Run this code

	
	fpath <- system.file("extdata", package="WrightMap")
	model1 <- CQmodel(p.est = file.path(fpath,"ex2.eap"), show = file.path(fpath,"ex2.shw"))
	
	#Person histogram, modern item
	ppPlot(model1,est = 0, SE = 1) 
	
	#Person density, classic item
	ppPlot(model1,est = 0, SE = 1, person.side = personDens,item.side = itemClassic)