ltm (version 0.8-9)

plot.fscores: Factor Scores - Ability Estimates Plot method

Description

Plots a Kernel Density Estimation of the distribution of the factor scores (i.e., person parameters). Provides also the option to include in the plot the item difficulty parameters (similar to the Item Person Maps).

Usage

## S3 method for class 'fscores':
plot(x, bw = "nrd0", adjust = 2, kernel = "gaussian", 
    include.items = FALSE, tol = 0.2, xlab = "Ability", ylab = "Density", 
    main = "Kernel Density Estimation for Ability Estimates", 
    pch = 16, cex = 1.5, \dots)

Arguments

x

an object inheriting from class fscores.

bw, adjust, kernel

arguments to density().

include.items

logical; if TRUE the item difficulty parameters are included in the plot.

tol

the tolerance used to group the item difficulty parameters, i.e., when include.items = TRUE the values round(betas / tol) * tol are plotted, where beta is the numeric vector of item difficulty param

xlab, ylab, main

character string or an expression; see title.

pch, cex

arguments to stripchart(); used when include.items = TRUE.

...

extra graphical parameters to be passed to plot.density().

See Also

factor.scores

Examples

## Factor Scores for LSAT data:
fsc <- factor.scores(rasch(LSAT))
plot(fsc, include.items = TRUE, main = "KDE for Person Parameters")
legend("left", "item parameters", pch = 16, cex = 1.5, bty = "n")