Selective Mixup for Debiasing Question Selection in Computerized Adaptive Testing

TL;DR

This paper introduces a debiasing framework for Computerized Adaptive Testing that mitigates selection bias and improves fairness and generalization in question selection by using a novel mixup-based regularization technique.

Contribution

The paper proposes a novel debiasing framework with Cross-Attribute Examinee Retrieval and Selective Mixup modules to address selection bias in CAT, enhancing fairness and accuracy.

Findings

Significant improvement in diagnosis model fairness.

Enhanced generalization ability of question selection.

Effective reduction of selection bias in experiments.

Abstract

Computerized Adaptive Testing (CAT) is a widely used technology for evaluating learners' proficiency in online education platforms. By leveraging prior estimates of proficiency to select questions and updating the estimates iteratively based on responses, CAT enables personalized learner modeling and has attracted substantial attention. Despite this progress, most existing works focus primarily on improving diagnostic accuracy, while overlooking the selection bias inherent in the adaptive process. Selection Bias arises because the question selection is strongly influenced by the estimated proficiency, such as assigning easier questions to learners with lower proficiency and harder ones to learners with higher proficiency. Since the selection depends on prior estimation, this bias propagates into the diagnosis model, which is further amplified during iterative updates, leading to misalignment and biased predictions. Moreover, the imbalanced nature of learners' historical interactions often exacerbates the bias in diagnosis models. To address this issue, we propose a debiasing framework consisting of two key modules: Cross-Attribute Examinee Retrieval and Selective Mixup-based Regularization. First, we retrieve balanced examinees with relatively even distributions of correct and incorrect responses and use them as neutral references for biased examinees. Then, mixup is applied between each biased examinee and its matched balanced counterpart under label consistency. This augmentation enriches the diversity of bias-conflicting samples and smooths selection boundaries. Finally, extensive experiments on two benchmark datasets with multiple advanced diagnosis models demonstrate that our method substantially improves both the generalization ability and fairness of question selection in CAT.