mirt (version 1.6.1)

testinfo: Function to calculate test information

Description

Given an estimated model compute the test information.

Usage

testinfo(x, Theta, degrees = NULL, group = NULL)

Arguments

x

an estimated mirt object

Theta

a matrix of latent trait values

degrees

a vector of angles in degrees that are between 0 and 90 that jointly sum to 90. Only applicable when the input object is multidimensional

group

a number signifying which group the item should be extracted from (applies to 'MultipleGroupClass' objects only)

Examples

dat <- expand.table(deAyala)
(mirt(dat, 1, '2PL', pars = 'values'))
mod <- mirt(dat, 1, '2PL', constrain = list(c(1,5,9,13,17)))

Theta <- matrix(seq(-4,4,.01))
tinfo <- testinfo(mod, Theta)
plot(Theta, tinfo, type = 'l')

#compare information loss between two tests
dat.smaller <- dat[,-c(1,2)]
mod2 <- mirt(dat.smaller, 1, '2PL', constrain = list(c(1,5,9)))
tinfo2 <- testinfo(mod2, Theta)

#removed item informations
plot(Theta, iteminfo(extract.item(mod, 1), Theta), type = 'l')
plot(Theta, iteminfo(extract.item(mod, 2), Theta), type = 'l')

#most loss of info around -1 when removing items 1 and 2; expected given item info functions
plot(Theta, tinfo2 - tinfo, type = 'l')