Person-Item Map for Explanatory IRT Models

This function creates a person-item map for an object returned from the eirm function. The function was modified from plotPImap in package eRm.

Usage

# S3 method for eirm
plot(
  x,
  difficulty = FALSE,
  sorted = TRUE,
  theta = NULL,
  main = "Person-Item Map",
  latdim = "Latent Dimension",
  pplabel = "Person\nParameter\nDistribution",
  cex.gen = 0.7,
  ...
)

Arguments

x: An object returned from the eirm function.
difficulty: Whether difficulty should be used instead of easiness (default: FALSE).
sorted: Whether the parameters should be sorted in the plot (default: TRUE).
theta: A vector of estimated theta values. If NULL, then theta values are obtained from the estimated eirm model. It might be better to save the theta values from a baseline model (e.g., Rasch) and use them when creating a person-item map.
main: Main title for the person-item map.
latdim: Label of the x-axis, i.e., the latent dimension.
pplabel: Title for the upper panel displaying the person parameter distribution.
cex.gen: A numerical value giving the amount by which plotting text and symbols should be magnified relative to the default. Here cex.gen applies to all text labels. The default is 0.7.
...: Other plot-related arguments.

Value

A person-item map.

Examples

data("VerbAgg")
mod0 <- eirm(formula = "r2 ~ -1 + situ + btype + (1|id)", data = VerbAgg)
plot(mod0)

plot(mod0, difficulty = TRUE) # Plot difficulty instead of easiness