Differential Item Functioning Analysis Without A Priori Information on Anchor Items: QQ Plots and Graphical Test

Ke-Hai Yuan (), Hongyun Liu () and Yuting Han ()
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Ke-Hai Yuan: University of Notre Dame
Hongyun Liu: Beijing Normal University
Yuting Han: Beijing Normal University

Psychometrika, 2021, vol. 86, issue 2, No 1, 345-377

Abstract: Abstract Differential item functioning (DIF) analysis is an important step in establishing the validity of measurements. Most traditional methods for DIF analysis use an item-by-item strategy via anchor items that are assumed DIF-free. If anchor items are flawed, these methods will yield misleading results due to biased scales. In this article, based on the fact that the item’s relative change of difficulty difference (RCD) does not depend on the mean ability of individual groups, a new DIF detection method (RCD-DIF) is proposed by comparing the observed differences against those with simulated data that are known DIF-free. The RCD-DIF method consists of a D-QQ (quantile quantile) plot that permits the identification of internal references points (similar to anchor items), a RCD-QQ plot that facilitates visual examination of DIF, and a RCD graphical test that synchronizes DIF analysis at the test level with that at the item level via confidence intervals on individual items. The RCD procedure visually reveals the overall pattern of DIF in the test and the size of DIF for each item and is expected to work properly even when the majority of the items possess DIF and the DIF pattern is unbalanced. Results of two simulation studies indicate that the RCD graphical test has Type I error rate comparable to those of existing methods but with greater power.

Keywords: differential item functioning; relative change of difficulty difference; RCD-QQ plot; confidence interval; graphical test (search for similar items in EconPapers)
Date: 2021
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DOI: 10.1007/s11336-021-09746-5

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