Differential Item Functioning classification for polytomously scored items

Abstract

Differential item functioning (DIF) refers to a difference in the way a test item functions for comparable groups of test takers. When there are DIF items in the test, it is necessary to make decisions concerning items revision or removal which cannot be based only on the outcome of DIF test statistic; a interpretable measure of the amount of DIF can help in decisions regarding DIF items. Due to the increasing use of polytomous item formats, this paper reviews the systems of DIF classification for polytomously scored items.

Keywords: DIF effect size, polytomous items; Liu-Agresti estimate; Signed Area; Standardized Mean Difference; polytomous SIBTEST; ordinal logistic model.