Anomaly pattern detection for streaming data

Outlier detection aims to find a data sample that is different from most other data samples. While outlier detection is performed at an individual instance level, anomaly pattern detection on a data stream means detecting a time point where a pattern to generate data is unusual and significantly different from normal behavior. Beyond predicting the outlierness of individual data samples in a data stream, it can be very useful to detect the occurrence of anomalous patterns in real time. In this paper, we propose a method for anomaly pattern detection in a data stream based on binary classification for outliers and statistical tests on a data stream of binary labels of normal or an outlier. In the first step, by applying the clustering-based outlier detection method, we transform a data stream into a stream of binary values where 0 stands for the prediction as normal data and 1 for outlier prediction. In the second step, anomaly pattern detection is performed on a stream of binary values by two approaches: testing the equality of parameters in the binomial distributions of a reference window and a detection window, and using control charts for the fraction defective. The proposed method obtained the average true positive detection rate of 94% in simulated experiments using real and artificial data. The experimental results also show that anomaly pattern occurrence can be detected reliably even when outlier detection performance is relatively low.