Model-Agnostic Meta Learning for Class Imbalance Adaptation

ACL ARR 2026 January Submission199 Authors

Keywords: Class imbalance, Meta-learning, Dynamic resampling, Semantic retrieval, Imbalance learning

Abstract:

Class imbalance is a widespread challenge in NLP tasks, significantly hindering robust performance across diverse domains and applications.
We introduce Hardness-Aware Meta-Resample (HAMR), a unified framework that adaptively addresses both class imbalance and data difficulty.
HAMR employs bi-level optimizations to dynamically estimate instance-level weights that prioritize genuinely challenging samples and minority classes, while a neighborhood-aware resampling mechanism amplifies training focus on hard examples and their semantically similar neighbors.
We validate HAMR on six imbalanced datasets covering multiple tasks and spanning biomedical, disaster response, and sentiment domains.
Experimental results show that HAMR achieves substantial improvements for minority classes and consistently outperforms strong baselines.
Extensive ablation studies demonstrate that our proposed modules synergistically contribute to performance gains and highlight HAMR as a flexible and generalizable approach for class imbalance adaptation.

Paper Type: Long

Research Area: Machine Learning for NLP

Research Area Keywords: Machine Learning for NLP, Information Extraction, Language Modeling

Contribution Types: NLP engineering experiment, Reproduction study, Approaches to low-resource settings

Languages Studied: English

Submission Number: 199