针对宫颈涂片数据不平衡问题,提出校准增强的集成分类方法。
Reliability-Aware Ensemble Classification Under Class Imbalance: A Calibration Study on Liquid-Based Cervical Cytology
- 用加权采样训练轻量模型,结合后验温度校准提升可靠性
- 校准显著降低误差指标,但对准确率等判别性能影响小
- 在该数据集上校准比增加集成规模更关键,适合医疗诊断
宫颈涂片分类模型通常在平衡数据集上评估,但真实世界液基宫颈细胞学(LBC)数据常规模小且类别不平衡。本文基于Mendeley LBC数据集,采用其原始四类Bethesda分类(NILM、LSIL、HSIL、SCC),开展类别不平衡与校准感知的集成分类研究。使用Swin-Tiny、TinyViT-5M、DenseNet121三种轻量架构,通过加权随机采样应对类别不平衡,并与两种软投票集成(Hybrid-2、Hybrid-3)对比。在每轮交叉验证中,从训练集中分离出独立校准子集,进行后验温度校准,避免因数据重用导致校准结果过乐观。结果显示,所有模型与集成配置经校准后,预期校准误差、Brier得分和负对数似然均显著下降,而准确率、宏平均F1和宏平均AUROC基本不变。集成规模未带来一致可靠性提升,最优个体模型经校准后已足够。混淆矩阵显示所有错误均集中在高分级病变(HSIL)与癌变(SCC)边界,无涉及阴性(NILM)或低分级(LSIL)类别。表明该校准是提升可靠性的主要手段,但结论受限于数据集规模较小。
原文摘要 · Abstract (English)
Cervical cytology classification models are typically evaluated on curated, class-balanced benchmarks, but real-world liquid-based cytology (LBC) collections are often small and class-imbalanced. This paper presents a class-imbalance-aware and calibration-aware ensemble classification study on the Mendeley LBC dataset, using its native four-class Bethesda taxonomy (NILM, LSIL, HSIL, SCC) rather than a collapsed binary formulation. Three lightweight architectures (Swin-Tiny, TinyViT-5M, DenseNet121) are trained directly on Mendeley LBC using weighted random sampling to counteract class imbalance, and compared against two soft-voting ensembles (Hybrid-2, Hybrid-3). Post-hoc temperature scaling is fit on a held-out calibration subset carved out of the training portion of each cross-validation fold, distinct from both the training data used to fit model weights and the evaluation fold used for final metrics, avoiding the optimistic calibration estimates that result when the same data is used for both purposes. Calibration substantially reduces expected calibration error, Brier score, and negative log-likelihood for every model and ensemble configuration tested, while discrimination metrics (accuracy, macro-F1, macro-AUROC) remain essentially unchanged. Ensemble size shows no consistent additional reliability benefit over the best individual model once all configurations are properly calibrated. Confusion matrices show that all classification errors, across every configuration, are confined to the boundary between high-grade lesions (HSIL) and carcinoma (SCC); no errors involve the negative (NILM) or low-grade (LSIL) categories. These results suggest that, for this dataset, calibration is the dominant lever for reliability, not ensemble size, though this conclusion should be read in light of the dataset's modest size.
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