Williams VSL. The "unbiased" anchor: bridging the gap between DIF and item bias. Appl Meas Educ. 1997;10(3):253-67. doi: 10.1207/s15324818ame1003_4

This research uses item response theory for the investigation of differential item functioning (DlF) and examines the advantages of using a multivariate external criterion to match examinees from the various subpopulations. An attempt was made to select a set of unbiased items to comprise the matching criterion. Expected course grades provided by the students' teachers were examined and found to function similarly across sex and race subgroups and were incorporated into the matching criterion. The inclusion of teachers' grades provides additional information in the extreme proficiency ranges and has the potential to enhance the validity of subgroup comparisons and ihferences of possible item bias. The use of an external matching criterion allows test developers to embed the same short, designated anchor in multiple test forms, thereby avoiding the circularity inherent to conventional DIF analyses and permitting comparison of DIF statistics across test forms.

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