Compute multidimensional difficulty index

Returns a matrix containing the MDIFF values (Reckase, 2009). Only supported for items of class 'dich' and 'graded'.

MDIFF(x, which.items = NULL, group = NULL)

Arguments

x

an object of class 'SingleGroupClass', or an object of class 'MultipleGroupClass' if a suitable group input were supplied

which.items

a vector indicating which items to select. If NULL is used (the default) then MDISC will be computed for all items

group

group argument to pass to extract.group function. Required when the input object is a multiple-group model

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

Reckase, M. D. (2009). Multidimensional Item Response Theory. Springer.

See also

extract.group, MDISC

Author

Phil Chalmers rphilip.chalmers@gmail.com

Examples

# \donttest{

mod <- mirt(Science, 2)
MDIFF(mod)
#>           MDIFF_1    MDIFF_2   MDIFF_3
#> Comfort -3.892829 -2.1408175 1.1974522
#> Work    -1.806316 -0.5623950 1.4163829
#> Future  -2.486824 -1.0433836 0.9256248
#> Benefit -2.316311 -0.6940864 1.1869606

mod <- mirt(expand.table(LSAT7), 2)
MDIFF(mod)
#>           MDIFF_1
#> Item.1 -1.2103885
#> Item.2 -0.7903375
#> Item.3 -0.8774460
#> Item.4 -0.6408048
#> Item.5 -2.4615393

# }