equate (version 1.2-0)

plot.equate: Plotting of Equating Functions

Description

This function plots equating functions from one or more objects of class equate.

Usage

## S3 method for class 'equate':
plot(..., add = FALSE, addident = TRUE, xpoints,
	ypoints, xlab = "Raw Scale", ylab = "Equated Scale",
	main = "Equating Plot", col = rainbow(length(x)),
	lty = 1, pchcol = "gray", addlegend = TRUE,
	legendtext, morepar = NULL)

Arguments

...

One or more equating objects, each containing results for equating the same two test forms.

add

logical, with default FALSE, specifying whether to create a new plot or add to the current one.

addident

logical, with default TRUE, for plotting the identity function

xpoints, ypoints

optional vectors of the same length containing raw scores on forms X and Y, assuming an equivalent-groups design

xlab, ylab, main, col, lty

graphical parameters passed to par, with the lengths of col and lty recycled as necessary

pchcol

color used when plotting xpoints and ypoints

addlegend

logical, with default TRUE, indicating whether or not a legend should be added

legendtext

character vector of text to be passed to the legend argument of the legend function, defaulting to a combination of the equating types and methods specified in each equating object

morepar

additional graphical parameters passed to par

Details

Equating functions are plotted as lines based on the concordance table for each equating object that is supplied. The resulting plot can be used to compare each function across the score scale.

Examples

nx <- freqtab(KBneat$x[, 1], xscale = 0:36,
	v = KBneat$x[, 2], vscale = 0:12)
ny <- freqtab(KBneat$y[, 1], xscale = 0:36,
	v = KBneat$y[, 2], vscale = 0:12)

neq1 <- equate(nx, ny, type = "Linear", method = "Tuck")
neq2 <- equate(nx, ny, type = "equip", method = "freq")
neq3 <- equate(nx, ny, type = "linear", method = "braun")

plot(neq1, neq2, neq3)