Calculates DFIT statistics using an object of class "lordif"
Usage
DFIT(obj)
Arguments
obj
an object of class "lordif"
Details
Calculates DFIT statistics, including the compensatory differential item functioning (CDIF),
the non-compensatory differential item functioning (NCDIF), and the differential test functioning (DTF),
based on an object returned from lordif.
Value
CDIF
a data frame of dimension ni by (ng-1), containing compensatory differential item functioning statistics for ni items and (ng-1) groups
NCDIF
a data frame containing non-compensatory differential item functioning statistics
DTF
the Differential Test Functioning (DTF) statistic (Raju, van der Linden, & Fleer, 1995)
ipar
a list of item parameter estimates by group
TCC
a list of test characteristic functions by group
Author(s)
Seung W. Choi <choi.phd@gmail.com>
References
Oshima, T., & Morris, S. (2008). Raju's differential functioning of items and tests (DFIT). Educational Measurement: Issues and Practice, 27, 43-50.
Raju, N. S., van der Linden, W. J., & Fleer, P. F., (1995). An IRT-based internal measure of test bias with application of differential item functioning. Applied Psychological Measurement, 19, 353-368.
See Also
lordif
Examples
##load PROMIS Anxiety sample data (n=766)
## Not run: data(Anxiety)
##age : 0=younger than 65 or 1=65 or older
##run age-related DIF on all 29 items (takes about a minute)
## Not run: age.DIF <- lordif(Anxiety[paste("R",1:29,sep="")],Anxiety$age)
##run DFIT
## Not run: age.DIF.DFIT <- DFIT(age.DIF)