probtrace {mirt}

Function to calculate probability trace lines

Description

Given an internal mirt object extracted from an estimated model, or the single-group estimated model itself, compute the probability trace lines for all categories.

Usage

probtrace(x, Theta)

Arguments

x

either an extracted internal mirt object containing item information (see extract.item) or a model of class SingleGroupClass typically returned by the function mirt or bfactor

Theta

a vector (unidimensional) or matrix (unidimensional/multidimensional) of latent trait values

Author(s)

Phil Chalmers [e-mail]

References

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

See Also

extract.item, extract.group

Examples

mod <- mirt(Science, 1)

# single item probabilty tracelines for Item 2
extr.2 <- extract.item(mod, 2)
Theta <- matrix(seq(-4,4, by = .1))
traceline <- probtrace(extr.2, Theta)
head(data.frame(traceline, Theta=Theta))

# probability tracelines for all items in test
tracelines <- probtrace(mod, Theta)
head(tracelines)