Plotting Equating Results

Description

Functions for plotting equating functions from one or more objects of class “equate” or “equate.list”.

Usage

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## S3 method for class 'equate'
plot(..., elist = NULL, add = FALSE, out = "eqs",
  xpoints, ypoints, addident = TRUE, identy, identcol = 1, rescale = c(0,
  1), xlab = "Total Score", ylab, col = rainbow(length(x)), pch, lty = 1,
  lwd = 1, subset, morepars = NULL, addlegend = TRUE, legendtext,
  legendplace = "bottomright")

## S3 method for class 'equate.list'
plot(x, ...)

Arguments

...

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

elist

list of equatings to be plotted.

add

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

out

character vector specifying the output to be plotted, either equating functions ("eqs"), standard errors ("se"), bias ("bias"), or RMSE ("rmse").

xpoints, ypoints

optional vectors of the same length containing raw scores on forms X and Y, assuming a single group or equivalent groups design.

addident

logical, with default TRUE, for plotting the identity function. The result depends on out.

identy

vector of y coordinates for plotting the identity line. Defaults to the X scale when out = "eqs", otherwise, a horizontal line with intercept 0.

identcol

color used for plotting the identity line.

rescale

intercept and slope, with default 0 and 1, used to rescale all lines before plotting.

xlab, ylab, col, pch, lty, lwd

graphical parameters passed to par, with col, pch, lty, and lwd recycled as necessary.

subset

vector for subsetting the output when multiple equating functions are included in x.

morepars

list of additional graphical parameters, excluding xlab, ylab, col, pch, lty, and lwd.

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.

legendplace

placement of the legend.

x

equate.list” object, containing output from multiple equatings.

Details

Equating functions (out = "eqs") are plotted as lines based on the concordance table for each equating object that is supplied. Standard errors (out = "se") default to bootstrap standard errors, if available, otherwise, analyitical standard errors are plotted. Bias (out = "bias") and RMSE (out = "rmse") are also taken from bootstrapping output.

Examples

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# See ?equate for additional examples

rx <- as.freqtab(ACTmath[, 1:2])
ry <- as.freqtab(ACTmath[, c(1, 3)])
set.seed(2007)

req1 <- equate(rx, ry, type = "i", boot = TRUE, reps = 5)
req2 <- equate(rx, ry, type = "m", boot = TRUE, reps = 5)
req3 <- equate(rx, ry, type = "l", boot = TRUE, reps = 5)
req4 <- equate(rx, ry, type = "e", boot = TRUE, reps = 5,
  smooth = "loglin", degree = 3)
req5 <- composite(list(req1, req2), wc = .5, symmetric = TRUE)

plot(req1, req2, req3, req4, req5[[1]], addident = FALSE)
plot(req5)