Anchor Selection Using the Wald Test Anchor-All-Test-All Procedure

Abstract

Methods for testing differential item functioning (DIF) require that the reference and focal groups are linked on a common scale using group-invariant anchor items. Several anchor-selection strategies have been introduced in an item response theory framework. However, popular strategies often utilize likelihood ratio testing with all-others-as-anchors that requires multiple model fittings. The current study explored alternative anchor-selection strategies based on a modified version of the Wald χ2 test that is implemented in flexMIRT and IRTPRO, and made comparisons with methods based on the popular likelihood ratio test. Accuracies of anchor identification of four different strategies (two testing methods combined with two selection criteria), along with the power and Type I error associated with respective follow-up DIF tests, will be presented. Implications for applied researchers and suggestions for future research will be discussed.