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Outlier detection refers to the identification of data points that deviate from a general data distribution. Existing unsupervised approaches often suffer from high computational cost, complex hyperparameter tuning, and limited…

Machine Learning · Computer Science 2022-08-26 Zheng Li , Yue Zhao , Xiyang Hu , Nicola Botta , Cezar Ionescu , George H. Chen

Outliers are ubiquitous in modern data sets. Distance-based techniques are a popular non-parametric approach to outlier detection as they require no prior assumptions on the data generating distribution and are simple to implement. Scaling…

Machine Learning · Statistics 2016-05-04 Mario Lucic , Olivier Bachem , Andreas Krause

Selecting and combining the outlier scores of different base detectors used within outlier ensembles can be quite challenging in the absence of ground truth. In this paper, an unsupervised outlier detector combination framework called DCSO…

Machine Learning · Computer Science 2019-11-26 Yue Zhao , Maciej K. Hryniewicki

In recent years, there have been many practical applications of anomaly detection such as in predictive maintenance, detection of credit fraud, network intrusion, and system failure. The goal of anomaly detection is to identify in the test…

Applications · Statistics 2020-06-12 Zekun Xu , Deovrat Kakde , Arin Chaudhuri

An outlier is an observation or a data point that is far from rest of the data points in a given dataset or we can be said that an outlier is away from the center of mass of observations. Presence of outliers can skew statistical measures…

Machine Learning · Computer Science 2021-06-17 Amulya Agarwal , Nitin Gupta

Modern machine learning-based recognition approaches require large-scale datasets with large number of labelled training images. However, such datasets are inherently difficult and costly to collect and annotate. Hence there is a great and…

Machine Learning · Computer Science 2019-12-30 Yanwei Fu , De-An Huang , Leonid Sigal

Outlier detection is an important problem occurring in a wide range of areas. Outliers are the outcome of fraudulent behaviour, mechanical faults, human error, or simply natural deviations. Many data mining applications perform outlier…

Machine Learning · Computer Science 2025-10-28 Juan A. Lara , David Lizcano , Víctor Rampérez , Javier Soriano

Outlier detection is a well-researched and crucial problem in machine learning. However, there is little research on string data outlier detection, as most literature focuses on outlier detection of numerical data. A robust string data…

Machine Learning · Computer Science 2026-03-13 Philip Maus

From the past decade outlier detection has been in use. Detection of outliers is an emerging topic and is having robust applications in medical sciences and pharmaceutical sciences. Outlier detection is used to detect anomalous behaviour of…

Computational Engineering, Finance, and Science · Computer Science 2013-12-13 Doreswamy , Chanabasayya . M. Vastrad

Outlier detection plays an essential role in many data-driven applications to identify isolated instances that are different from the majority. While many statistical learning and data mining techniques have been used for developing more…

Machine Learning · Computer Science 2018-05-08 Ninghao Liu , Donghwa Shin , Xia Hu

This paper presents a batch-wise density-based clustering approach for local outlier detection in massive-scale datasets. Unlike the well-known traditional algorithms, which assume that all the data is memory-resident, our proposed method…

Machine Learning · Computer Science 2021-07-06 Sayyed Ahmad Naghavi Nozad , Maryam Amir Haeri , Gianluigi Folino

Unsupervised learning methods are well established in the area of anomaly detection and achieve state of the art performances on outlier datasets. Outliers play a significant role, since they bear the potential to distort the predictions of…

Machine Learning · Computer Science 2024-07-02 Andreas Lohrer , Daniyal Kazempour , Maximilian Hünemörder , Peer Kröger

Outlier detection is one of the most popular and continuously rising topics in the data mining field due to its crucial academic value and extensive industrial applications. Among different settings, unsupervised outlier detection is the…

Machine Learning · Computer Science 2021-08-03 Sibo Zhu , Handong Zhao , Hongfu Liu

Normalizing flows are prominent deep generative models that provide tractable probability distributions and efficient density estimation. However, they are well known to fail while detecting Out-of-Distribution (OOD) inputs as they directly…

Machine Learning · Computer Science 2021-11-17 Nishant Kumar , Pia Hanfeld , Michael Hecht , Michael Bussmann , Stefan Gumhold , Nico Hoffmann

Outlier detection holds significant importance in the realm of data mining, particularly with the growing pervasiveness of data acquisition methods. The ability to identify outliers in data streams is essential for maintaining data quality…

Dynamic factor models have a wide range of applications in econometrics and applied economics. The basic motivation resides in their capability of reducing a large set of time series to only few indicators (factors). If the number of time…

Statistics Theory · Mathematics 2009-09-29 Roberto Baragona , Francesco Battaglia

Outlier detection refers to the identification of anomalous samples that deviate significantly from the distribution of normal data and has been extensively studied and used in a variety of practical tasks. However, most unsupervised…

Machine Learning · Computer Science 2025-01-07 Can Gao , Xiaofeng Tan , Jie Zhou , Weiping Ding , Witold Pedrycz

Most of existing outlier detection methods assume that the outlier factors (i.e., outlierness scoring measures) of data entities (e.g., feature values and data objects) are Independent and Identically Distributed (IID). This assumption does…

Machine Learning · Computer Science 2021-03-23 Guansong Pang , Longbing Cao , Ling Chen

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

We propose two new outlier detection methods, for identifying and classifying different types of outliers in (big) functional data sets. The proposed methods are based on an existing method called Massive Unsupervised Outlier Detection…

Methodology · Statistics 2021-10-15 Oluwasegun Taiwo Ojo , Antonio Fernández Anta , Rosa E. Lillo , Carlo Sguera