Differential Item Functioning: Beyond validity evidence based on internal structure

Background: In the latest release of the Standards for Educational and Psychological Testing, Differential Item Functioning (DIF) is considered as validity evidence based on internal structure. However, there are no indications of how to design a DIF study as a validation study. In this paper, we propose relating DIF to all sources of validity evidence, and provide a general conceptual framework for transforming "typical" DIF studies into validation studies. Method: We perform a comprehensive review of the literature and make theoretical and practical proposals. Results: The article provides arguments in favour of addressing DIF detection and interpretation as validation studies, and suggestions for conducting DIF validation studies. Discussion: The combination of quantitative and qualitative data within a mixed methods research perspective, along with planning DIF studies as validation studies, can help improve the validity of test score interpretations.