plot.ltm {ltm}R Documentation

Plot method for ltm objects

Description

Produces the Item Characteristic Curves or Surfaces for fitted ltm objects.

Usage

plot.ltm(x, cx = NULL, cy = NULL, ...)

Arguments

x an object inheriting from class ltm.
cx the x-coordinate to be passed to legend. Used only for the one-factor model.
cy the y-coordinate to be passed to legend. Used only for the one-factor model.
... extra graphical parameters to be passed to lines (one-factor case) or to persp (two-factors case).

Details

Item characteristic curves (also known as item response functions) show how the probability of a positive response, in each item, increases with the values of the latent variables.

If x is a linear two-factor model, then the plot of the standardized loadings (see coef.ltm) is also produced.

Note

When two latent variables are used, plot.ltm uses options(graphics.record = TRUE), i.e., the plots are available for scrolling.

See Also

ltm

Examples


## Item Characteristic Curves for the one-factor model:
m <- ltm(Wirs~z1)
plot(m)

## Not run: 
## because of an error during R CMD CHECK; you can run it.
## Item Characteristic Surfaces for the interaction model:
m <- ltm(Wirs~z1*z2)
plot(m)
## End(Not run)

[Package ltm version 0.1-1 Index]