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Detecting test data deviating from training data is a central problem for safe and robust machine learning. Likelihoods learned by a generative model, e.g., a normalizing flow via standard log-likelihood training, perform poorly as an…

Machine Learning · Computer Science 2023-04-28 Robert Schmier , Ullrich Köthe , Christoph-Nikolas Straehle

Outlier detection is an inevitable step to most statistical data analyses. However, the mere detection of an outlying case does not always answer all scientific questions associated with that data point. Outlier detection techniques,…

Methodology · Statistics 2019-12-12 Michiel Debruyne , Sebastiaan Höppner , Sven Serneels , Tim Verdonck

The problem of outlier detection is extremely challenging in many domains such as text, in which the attribute values are typically non-negative, and most values are zero. In such cases, it often becomes difficult to separate the outliers…

Information Retrieval · Computer Science 2017-01-06 Ramakrishnan Kannan , Hyenkyun Woo , Charu C. Aggarwal , Haesun Park

We present a novel notion of outlier, called the Concentration Free Outlier Factor, or CFOF. As a main contribution, we formalize the notion of concentration of outlier scores and theoretically prove that CFOF does not concentrate in the…

Machine Learning · Computer Science 2019-09-18 Fabrizio Angiulli

Circle fitting methods are extensively utilized in various industries, particularly in quality control processes and design applications. The effectiveness of these algorithms can be significantly compromised when the point sets to be…

Computer Vision and Pattern Recognition · Computer Science 2025-08-07 Ahmet Gökhan Poyraz

Outlier detection algorithms typically assign an outlier score to each observation in a dataset, indicating the degree to which an observation is an outlier. However, these scores are often not comparable across algorithms and can be…

Machine Learning · Computer Science 2024-10-31 Philipp Röchner , Henrique O. Marques , Ricardo J. G. B. Campello , Arthur Zimek , Franz Rothlauf

The outlying property detection problem is the problem of discovering the properties distinguishing a given object, known in advance to be an outlier in a database, from the other database objects. In this paper, we analyze the problem…

Machine Learning · Computer Science 2013-06-18 Fabrizio Angiulli , Fabio Fassetti , Luigi Palopoli , Giuseppe Manco

Real data often contain anomalous cases, also known as outliers. These may spoil the resulting analysis but they may also contain valuable information. In either case, the ability to detect such anomalies is essential. A useful tool for…

Machine Learning · Statistics 2021-01-13 Peter J. Rousseeuw , Mia Hubert

Many well-established anomaly detection methods use the distance of a sample to those in its local neighbourhood: so-called `local outlier methods', such as LOF and DBSCAN. They are popular for their simple principles and strong performance…

Machine Learning · Computer Science 2021-12-13 Adam Goodge , Bryan Hooi , See Kiong Ng , Wee Siong Ng

High-dimensional data poses unique challenges in outlier detection process. Most of the existing algorithms fail to properly address the issues stemming from a large number of features. In particular, outlier detection algorithms perform…

Machine Learning · Computer Science 2020-09-22 Firuz Kamalov , Ho Hon Leung

Recognition of anomalous events is a challenging but critical task in many scientific and industrial fields, especially when the properties of anomalies are unknown. In this paper, we introduce a new anomaly concept called "unicorn" or…

Machine Learning · Computer Science 2022-01-13 Zsigmond Benkő , Tamás Bábel , Zoltán Somogyvári

Outlier detection is one of the most important processes taken to create good, reliable data in machine learning. The most methods of outlier detection leverage an auxiliary reconstruction task by assuming that outliers are more difficult…

Computer Vision and Pattern Recognition · Computer Science 2022-11-23 Ning Huyan , Dou Quan , Xiangrong Zhang , Xuefeng Liang , Jocelyn Chanussot , Licheng Jiao

In a corpus of data, outliers are either errors: mistakes in the data that are counterproductive, or are unique: informative samples that improve model robustness. Identifying outliers can lead to better datasets by (1) removing noise in…

Outlier detection is a critical task in data mining, aimed at identifying objects that significantly deviate from the norm. Semi-supervised methods improve detection performance by leveraging partially labeled data but typically overlook…

Machine Learning · Computer Science 2025-12-23 Baiyang Chen , Zhong Yuan , Zheng Liu , Dezhong Peng , Yongxiang Li , Chang Liu , Guiduo Duan

Outlier detection, crucial for identifying unusual patterns with significant implications across numerous applications, has drawn considerable research interest. Existing semi-supervised methods typically treat data as purely numerical and}…

Machine Learning · Computer Science 2025-12-23 Baiyang Chen , Zhong Yuan , Dezhong Peng , Hongmei Chen , Xiaomin Song , Huiming Zheng

Detecting Out-of-distribution (OOD) inputs have been a critical issue for neural networks in the open world. However, the unstable behavior of OOD detection along the optimization trajectory during training has not been explored clearly. In…

Machine Learning · Computer Science 2023-03-03 Zhen Cheng , Fei Zhu , Xu-Yao Zhang , Cheng-Lin Liu

Modern neural networks are known to give overconfident prediction for out-of-distribution inputs when deployed in the open world. It is common practice to leverage a surrogate outlier dataset to regularize the model during training, and…

Machine Learning · Computer Science 2024-02-27 Wenyu Jiang , Hao Cheng , Mingcai Chen , Chongjun Wang , Hongxin Wei

Out-of-distribution detection (OOD) deals with anomalous input to neural networks. In the past, specialized methods have been proposed to reject predictions on anomalous input. Similarly, it was shown that feature extraction models in…

Machine Learning · Computer Science 2022-01-25 Jan Diers , Christian Pigorsch

Out-of-Distribution (OOD) detection, aiming to distinguish outliers from known categories, has gained prominence in practical scenarios. Recently, the advent of vision-language models (VLM) has heightened interest in enhancing OOD detection…

Computer Vision and Pattern Recognition · Computer Science 2025-02-27 Fanhu Zeng , Zhen Cheng , Fei Zhu , Hongxin Wei , Xu-Yao Zhang

Advances in sensor technology have enabled the collection of large-scale datasets. Such datasets can be extremely noisy and often contain a significant amount of outliers that result from sensor malfunction or human operation faults. In…

Machine Learning · Computer Science 2018-08-28 Yu-Hsuan Kuo , Zhenhui Li , Daniel Kifer