DIF function

Exploratory test for Differential Item Functioning

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

Returns

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.

Details

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

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)

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