Outlier Explanation via Sum-Product Networks

TL;DR

This paper introduces a novel outlier explanation method using Sum-Product Networks, enabling efficient backward elimination and achieving state-of-the-art results in identifying features that distinguish outliers.

Contribution

The paper proposes a new outlier explanation algorithm based on Sum-Product Networks that improves computational efficiency and accuracy over existing search-based methods.

Findings

Achieves state-of-the-art outlier explanation performance

Enables efficient backward elimination using SPNs

Outperforms recent deep learning-based explanation methods

Abstract

Outlier explanation is the task of identifying a set of features that distinguish a sample from normal data, which is important for downstream (human) decision-making. Existing methods are based on beam search in the space of feature subsets. They quickly becomes computationally expensive, as they require to run an outlier detection algorithm from scratch for each feature subset. To alleviate this problem, we propose a novel outlier explanation algorithm based on Sum-Product Networks (SPNs), a class of probabilistic circuits. Our approach leverages the tractability of marginal inference in SPNs to compute outlier scores in feature subsets. By using SPNs, it becomes feasible to perform backwards elimination instead of the usual forward beam search, which is less susceptible to missing relevant features in an explanation, especially when the number of features is large. We empirically show that our approach achieves state-of-the-art results for outlier explanation, outperforming recent search-based as well as deep learning-based explanation methods