expected.item {mirt} | R Documentation |
Given an internal mirt object extracted from an estimated model compute the expected value for an item given the ability parameter(s).
expected.item(x, Theta, min = 0)
x |
an extracted internal mirt object containing item information (see |
Theta |
a vector (unidimensional) or matrix (multidimensional) of latent trait values |
min |
a constant value added to the expected values indicating the lowest theoretical category. Default is 0 |
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(-6,6, length.out=200))
expected <- expected.item(extr.2, Theta, min(Science[,1])) #min() of first item
head(data.frame(expected, Theta=Theta))
## expected Theta
## 1 1.013391 -6.000000
## 2 1.014407 -5.939698
## 3 1.015498 -5.879397
## 4 1.016672 -5.819095
## 5 1.017933 -5.758794
## 6 1.019289 -5.698492