Centering the Margins: Outlier-Based Identification of Harmed Populations in Toxicity Detection.

A standard method for measuring the impacts of AI on marginalized communities is to determine performance discrepancies between specified demographic groups. These approaches aim to address harms toward vulnerable groups, but they obscure harm patterns faced by intersectional subgroups or shared across demographic groups. We instead operationalize "the margins" as data points that are statistical outliers due to having demographic attributes distant from the "norm" and measure harms toward these outliers. We propose a Group-Based Performance Disparity Index (GPDI) that measures the extent to which a subdivision of a dataset into subgroups identifies those facing increased harms. We apply our approach to detecting disparities in toxicity detection and find that text targeting outliers is 28% to 86% more toxic for all types of toxicity examined. We also discover that model performance is consistently worse for demographic outliers, with disparities in error between outliers and non-outliers ranging from 28% to 71% across toxicity types. Our outlier-based analysis has comparable or higher GPDI than traditional subgroup-based analyses, suggesting that outlier analysis enhances identification of subgroups facing greater harms. Finally, we find that minoritized racial and religious groups are most associated with outliers, which suggests that outlier analysis is particularly beneficial for identifying harms against those groups.