plot.ltm {ltm} | R Documentation |
Produces the Item Characteristic Curves or Surfaces for fitted ltm
objects.
plot.ltm(x, cx = NULL, cy = NULL, ...)
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). |
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.
When two latent variables are used, plot.ltm
uses options(graphics.record = TRUE)
, i.e.,
the plots are available for scrolling.
## 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)