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arXiv 2012.12931cs.LGstat.ML
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使用分类数据集评估图级离群点检测:特殊观察和新见解

On Using Classification Datasets to Evaluate Graph-Level Outlier Detection: Peculiar Observations and New Insights

Carnegie Mellon University(卡内基梅隆大学)

Lingxiao Zhao, Leman Akoglu

摘要:

离群值挖掘社区的常见做法是将分类数据集重新用于评估各种检测模型。为此,通常使用二进制分类数据集,其中来自一个类的样本被指定为内点样本,而另一个类被大幅下采样以创建地面实况离群样本。图级离群点检测(GLOD)很少被研究,但有许多潜在的影响现实世界的应用。在这项研究中,我们确定了一个有趣的问题,重新利用图分类数据集的GLOD。我们发现模型的ROC-AUC性能会发生显着变化(从高翻转到非常低,甚至比随机更差),具体取决于哪个类被下采样。有趣的是,这两个变体的ROC-AUC约为1,并且对于某个基于传播的离群值检测模型家族,它们的性能差距随着传播的增加而放大。我们仔细研究了基于传播的模型产生的图嵌入空间,并发现了两个驱动因素:(1)传播放大的类内密度之间的差异,以及(2)跨类的重叠支持(嵌入的混合)。我们还研究了其他图嵌入方法和下游离群值检测器,发现有趣的性能翻转问题仍然广泛存在,但哪个版本的下采样实现更高的性能可能会有所不同。对综合结果的深入分析进一步加深了我们对既定问题的理解。

英文摘要:

It is common practice of the outlier mining community to repurpose classification datasets toward evaluating various detection models. To that end, often a binary classification dataset is used, where samples from one of the classes is designated as the inlier samples, and the other class is substantially down-sampled to create the ground-truth outlier samples. Graph-level outlier detection (GLOD) is rarely studied but has many potentially influential real-world applications. In this study, we identify an intriguing issue with repurposing graph classification datasets for GLOD. We find that ROC-AUC performance of the models changes significantly (flips from high to very low, even worse than random) depending on which class is down-sampled. Interestingly, ROC-AUCs on these two variants approximately sum to 1 and their performance gap is amplified with increasing propagations for a certain family of propagation based outlier detection models. We carefully study the graph embedding space produced by propagation based models and find two driving factors: (1) disparity between within-class densities which is amplified by propagation, and (2)overlapping support (mixing of embeddings) across classes. We also study other graph embedding methods and downstream outlier detectors, and find that the intriguing performance flip issue still widely exists but which version of the downsample achieves higher performance may vary. Thoughtful analysis over comprehensive results further deeper our understanding of the established issue.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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