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The Impact of Population Shift on Equating and Differential Item Functioning of Anchor Items: An Empirical Study DIF

Qu, Yanxuan; Wei, Youhua; Morgan, Rick
Publication Year:
Report Number:
ETS Research Memorandum
Document Type:
Page Count:
Subject/Key Words:
Population Growth, Population Invariance, Differential Item Functioning (DIF), Linking, Equating, Anchor Items, First Language


The analyses of this study revealed that the impact of population shift on linking and anchor DIF was small when the degree of population shift was low. However, as the degree of population shift reached beyond a certain level, linking results became substantially different from the baseline and more anchor items were flagged with DIF. The results indicated that linking can be inadequate and actions are needed to improve the quality of linking when population shift is severe.

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