ggWrightMap {ShinyItemAnalysis} | R Documentation |
ggplot2
This function allows to generate Wright map (also called
person-item map) using ggplot()
function from the ggplot2
package. Wright map is used to jointly display histogram of abilities
(or other measured trait) and item difficulty parameters.
Function takes pre-estimated parameter estimates, such as those obtained
from an IRT model.
ggWrightMap( theta, b, binwidth = 0.5, color = "blue", size = 15, item.names, ylab.theta = "Respondent latent trait", ylab.b = "Item difficulty", rel_widths = c(1, 1) )
theta |
numeric: vector of ability estimates. |
b |
numeric: vector of difficulty estimates. |
binwidth |
numeric: the width of the bins of histogram. |
color |
character: color of histogram. |
size |
text size in pts. |
item.names |
names of items to be displayed. |
ylab.theta |
character: description of y-axis for the histogram. |
ylab.b |
character: description of y-axis for the plot of difficulty estimates. |
rel_widths |
numeric: vector of length 2 specifying ratio of "facet's" widths. |
Adela Hladka
Institute of Computer Science of the Czech Academy of Sciences
hladka@cs.cas.cz
Jan Netik
Institute of Computer Science of the Czech Academy of Sciences
netik@cs.cas.cz
Patricia Martinkova
Institute of Computer Science of the Czech Academy of Sciences
martinkova@cs.cas.cz
Wright, B. & Stone, M. (1979). Best test design. MESA Press: Chicago, IL
library(mirt) # fit Rasch model with the mirt package fit <- mirt(HCI[, 1:20], model = 1, itemtype = "Rasch") # factor scores theta <- as.vector(fscores(fit)) # difficulty estimates using IRT parametrization b <- coef(fit, simplify = TRUE, IRTpars = TRUE)$items[, "b"] # Wright map ggWrightMap(theta, b) # Wright map with modified item names item.names <- paste("Item", 1:20) ggWrightMap(theta, b, item.names = item.names) # Wright map with modified descriptions of y-axis and relative widths of plots ggWrightMap(theta, b, ylab.theta = "Latent trait", ylab.b = "Difficulty estimates", rel_widths = c(2, 1) )