Function to calculate item information
Given an internal mirt item object extracted by using extract.item,
compute the item information.
iteminfo(x, Theta, degrees = NULL, total.info = TRUE, multidim_matrix = FALSE)
x |
an extracted internal mirt object containing item information (see |
Theta |
a vector (unidimensional) or matrix (multidimensional) of latent trait values |
degrees |
a vector of angles in degrees that are between 0 and 90. Only applicable when the input object is multidimensional |
total.info |
logical; return the total information curve for the item? If |
multidim_matrix |
logical; compute the information matrix for each row in |
Phil Chalmers rphilip.chalmers@gmail.com
Chalmers, R., P. (2012). mirt: A Multidimensional Item Response Theory Package for the R Environment. Journal of Statistical Software, 48(6), 1-29. doi: 10.18637/jss.v048.i06
mod <- mirt(Science, 1)
extr.2 <- extract.item(mod, 2)
Theta <- matrix(seq(-4,4, by = .1))
info.2 <- iteminfo(extr.2, Theta)
#do something with the info?
plot(Theta, info.2, type = 'l', main = 'Item information')
## Not run:
#category information curves
cat.info <- iteminfo(extr.2, Theta, total.info = FALSE)
plot(Theta, cat.info[,1], type = 'l', ylim = c(0, max(cat.info)),
ylab = 'info', main = 'Category information')
for(i in 2:ncol(cat.info))
lines(Theta, cat.info[,i], col = i)
## Customized test information plot
T1 <- T2 <- 0
dat <- expand.table(LSAT7)
mod1 <- mirt(dat, 1)
mod2 <- mirt(dat, 1, 'Rasch')
for(i in 1:5){
T1 <- T1 + iteminfo(extract.item(mod1, i), Theta)
T2 <- T2 + iteminfo(extract.item(mod2, i), Theta)
}
plot(Theta, T2/T1, type = 'l', ylab = 'Relative Test Information', las = 1)
lines(Theta, T1/T1, col = 'red')
# multidimensional
mod <- mirt(dat, 2, TOL=1e-2)
ii <- extract.item(mod, 1)
Theta <- as.matrix(expand.grid(-4:4, -4:4))
iteminfo(ii, Theta, degrees=c(45,45)) # equal angle
iteminfo(ii, Theta, degrees=c(90,0)) # first dimension only
# information matrices
iteminfo(ii, Theta, multidim_matrix = TRUE)
iteminfo(ii, Theta[1, , drop=FALSE], multidim_matrix = TRUE)
## End(Not run)Please choose more modern alternatives, such as Google Chrome or Mozilla Firefox.