DIF {dexter}

Exploratory test for Differential Item Functioning

Description

Exploratory test for Differential Item Functioning

Usage

DIF(dataSrc, person_property, predicate = NULL)

Arguments

dataSrc

a connection to a dexter database or a data.frame with columns: person_id, item_id, item_score

person_property

Defines groups of persons to calculate DIF

predicate

An optional expression to subset data, if NULL all data is used

Details

Tests for equality of relative item/category difficulties across groups. Supplements the confirmatory approach of the profile plot.

Value

An object of class DIF_stats holding statistics for overall-DIF and a matrix of statistics for DIF in the relative position of item-category parameters in the beta-parameterization where they represent locations on the ability scale where adjacent categories are equally likely. If there is DIF, the function 'plot' can be used to produce an image of the pairwise DIF statistics.

References

Bechger, T. M. and Maris, G (2015); A Statistical Test for Differential Item Pair Functioning. Psychometrika. Vol. 80, no. 2, 317-340.

See Also

A plot of the result is produced by the function plot.DIF_stats

Examples

db = start_new_project(verbAggrRules, ":memory:", person_properties=list(gender='unknown'))
add_booklet(db, verbAggrData, "agg")
dd = DIF(db,person_property="gender")
print(dd)
plot(dd)
str(dd)

close_project(db)