gen.difficulty {mirt} | R Documentation |
Function provides the four generalized item difficulty representations for polytomous response models described by Ali, Chang, and Anderson (2015). These estimates are used to gauge how difficult a polytomous item may be.
gen.difficulty(mod, type = "IRF", interval = c(-30, 30), ...)
mod |
a single factor model estimated by |
type |
type of generalized difficulty parameter to report.
Can be |
interval |
interval range to search for |
... |
additional arguments to pass to |
Phil Chalmers rphilip.chalmers@gmail.com
Ali, U. S., Chang, H.-H., & Anderson, C. J. (2015). Location indices for ordinal polytomous items based on item response theory (Research Report No. RR-15-20). Princeton, NJ: Educational Testing Service. http://dx.doi.org/10.1002/ets2.12065
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
## No test:
mod <- mirt(Science, 1)
coef(mod, simplify=TRUE, IRTpars = TRUE)$items
## a b1 b2 b3
## Comfort 1.041755 -4.669193 -2.5341299 1.4072541
## Work 1.225962 -2.385068 -0.7350678 1.8488053
## Future 2.293372 -2.282226 -0.9652918 0.8562529
## Benefit 1.094915 -3.057698 -0.9056673 1.5419094
gen.difficulty(mod)
## Comfort Work Future Benefit
## -2.3089094 -0.5741303 -0.9207845 -0.8530161
gen.difficulty(mod, type = 'mean')
## Comfort Work Future Benefit
## -1.9320231 -0.4237770 -0.7970883 -0.8071519
# also works for dichotomous items (though this is unnecessary)
dat <- expand.table(LSAT7)
mod <- mirt(dat, 1)
coef(mod, simplify=TRUE, IRTpars = TRUE)$items
## a b g u
## Item.1 0.9879254 -1.8787456 0 1
## Item.2 1.0808847 -0.7475160 0 1
## Item.3 1.7058006 -1.0576962 0 1
## Item.4 0.7651853 -0.6351358 0 1
## Item.5 0.7357980 -2.5204102 0 1
gen.difficulty(mod)
## Item.1 Item.2 Item.3 Item.4 Item.5
## -1.8787448 -0.7475182 -1.0576961 -0.6351601 -2.5204127
gen.difficulty(mod, type = 'mean')
## Item.1 Item.2 Item.3 Item.4 Item.5
## -1.8787456 -0.7475160 -1.0576962 -0.6351358 -2.5204102
## End(No test)