gDiscrim: Generalized Item Discrimination
In kitdouble/ShinyIRT: Test and Item Analysis via Shiny

Description Usage Arguments Details Note Author(s) References See Also Examples

Generalized item discrimination functions is generalized version of discrim function from psychometric package. It computes discrimination of an item, i.e. the ablitity for a specific items to distinguish among upper and lower ability individuals on a test, where number of groups, upper and lower group can be specified by user.

1	gDiscrim(x, k = 3, l = 1, u = 3)

`x`	matrix or data.frame of items to be examined. Rows represent persons, columns reperesent items.
`k`	numeric: number of groups to which may be data.frame x divided by the total score. Default value is 3. See Details.
`l`	numeric: lower group. Default value is 1. See Details.
`u`	numeric: upper group. Default value is 3. See Details.

The function takes data on individuals, computes their total test score and then divides individuals into k groups. The lower and upper group are determined by l and u parameters, i.e. l-th and u-th group where the ordering is defined by increasing total score.

gDiscrim is used by DDplot function.

Adela Drabinova
Institute of Computer Science, The Czech Academy of Sciences
Faculty of Mathematics and Physics, Charles University
drabinova@cs.cas.cz

Lubos Stepanek
First Faculty of Medicine, Charles University
lubomir.stepanek@lf1.cuni.cz

Patricia Martinkova
Institute of Computer Science, The Czech Academy of Sciences
martinkova@cs.cas.cz

Martinkova, P., Stepanek, L., Drabinova, A., Houdek, J., Vejrazka, M., & Stuka, C. (2017). Semi-real-time analyses of item characteristics for medical school admission tests. In: Proceedings of the 2017 Federated Conference on Computer Science and Information Systems.

discrim, DDplot

## Not run: 
# loading 100-item medical admission test data set
data(dataMedical)
x <- dataMedical[, 1:100]

# discrimination as in discrim() function from psychometric package
# compare to psychometric::discrim(x)
gDiscrim(x)

# 5 groups, compare 4th and 5th
gDiscrim(x, k = 5, l = 4, u = 5)

## End(Not run)