The Investigation of Differential Item Functioning in Adaptive Tests

Abstract

Differential item functioning (DIF) refers to a difference in item performance between equally proficient members of two demographic groups. From an item response theory (IRT) perspective, DIF can be defined as a difference between groups in item response functions. The classic example of a DIF item is a mathematics question containing sports jargon that is more likely to be understood by men than by women. An item of this kind would be expected to manifest DIF against women: They are less likely to give a correct response than men with equivalent math ability. In reality, the causes of DIF are often far more obscure. Camilli and Shepard (1994) and Holland andWainer (1993) provide an excellent background in the history, theory, and practice of DIF analysis.