Uncertainty in Additive Feature Attribution methods

TL;DR

This paper investigates uncertainty in additive feature attribution methods in XAI, proposing new measures and modifications to improve explanation reliability and understanding of model complexity.

Contribution

It introduces a framework for quantifying uncertainty, proposes a sampling modification for LIME, and analyzes how model complexity affects explanation uncertainty.

Findings

Little correlation between feature attribution and uncertainty.

Sampling modifications can reduce feature uncertainty.

Model complexity correlates with increased explanation uncertainty.

Abstract

In this work, we explore various topics that fall under the umbrella of Uncertainty in post-hoc Explainable AI (XAI) methods. We in particular focus on the class of additive feature attribution explanation methods. We first describe our specifications of uncertainty and compare various statistical and recent methods to quantify the same. Next, for a particular instance, we study the relationship between a feature's attribution and its uncertainty and observe little correlation. As a result, we propose a modification in the distribution from which perturbations are sampled in LIME-based algorithms such that the important features have minimal uncertainty without an increase in computational cost. Next, while studying how the uncertainty in explanations varies across the feature space of a classifier, we observe that a fraction of instances show near-zero uncertainty. We coin the term "stable instances" for such instances and diagnose factors that make an instance stable. Next, we study how an XAI algorithm's uncertainty varies with the size and complexity of the underlying model. We observe that the more complex the model, the more inherent uncertainty is exhibited by it. As a result, we propose a measure to quantify the relative complexity of a blackbox classifier. This could be incorporated, for example, in LIME-based algorithms' sampling densities, to help different explanation algorithms achieve tighter confidence levels. Together, the above measures would have a strong impact on making XAI models relatively trustworthy for the end-user as well as aiding scientific discovery.