Differential Item Functioning in rehabilitation research

Measurement is critical to Rehabilitation practice and research. To provide effective services and to have valid research results, it is imperative to have valid and reliable assessment tools. Differential Item Functioning (DIF) is a statistical procedure which better enables us to assess both the validity and the results of measurement instruments. As such, it is a methodology that can be very beneficial to the field of Rehabilitation. The purposes of this article are to (a) explain the fundamental principles and components of DIF, (b) discuss the practical implications of DIF for the Rehabilitation discipline, and (c) provide an example of DIF implementation and interpretation of results.