🤖 AI Summary
When conventional parametric item response models are misspecified, detecting differential item functioning (DIF) for binary items becomes challenging. To address this, we propose a nonparametric DIF detection method based on kernel smoothing. Our approach directly estimates and compares item response curves (IRCs) across groups without assuming any specific parametric item response model. We develop a novel nonparametric testing framework tailored to binary responses, derive an analytical expression for the asymptotic variance, design an optimal weighting function, and employ wild bootstrap for robust statistical inference. Simulation studies demonstrate that the method maintains well-controlled Type I error rates and achieves substantially higher statistical power than logistic regression—particularly under complex scenarios such as multiple IRC crossings. Empirical analysis further reveals that our method successfully identifies subtle DIF patterns overlooked by standard parametric models.
📝 Abstract
This study introduces a novel nonparametric approach for detecting Differential Item Functioning (DIF) in binary items through direct comparison of Item Response Curves (IRCs). Building on prior work on nonparametric comparison of regression curves, we extend the methodology to accommodate binary response data, which is typical in psychometric applications. The proposed approach includes a new estimator of the asymptotic variance of the test statistic and derives optimal weight functions that maximise local power. Because the asymptotic distribution of the resulting test statistic is unknown, a wild bootstrap procedure is applied for inference. A Monte Carlo simulation study demonstrates that the nonparametric approach effectively controls Type I error and achieves power comparable to the traditional logistic regression method, outperforming it in cases with multiple intersections of the underlying IRCs. The impact of bandwidth and weight specification is explored. Application to a verbal aggression dataset further illustrates the method's ability to detect subtle DIF patterns missed by parametric models. Overall, the proposed nonparametric framework provides a flexible and powerful alternative for detecting DIF, particularly in complex scenarios where traditional model-based assumptions may not be applicable.