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Data-driven software is increasingly being used as a critical component of automated decision-support systems. Since this class of software learns its logic from historical data, it can encode or amplify discriminatory practices. Previous research on algorithmic fairness has focused on improving “average-case” fairness. On the other hand, fairness at the extreme ends of the spectrum, which often signifies lasting and impactful shifts in societal attitudes, has received significantly less emphasis. Leveraging the statistics of extreme value theory (EVT), we propose a novel fairness criterion called extreme counterfactual discrimination (ECD). This criterion estimates the worst-case amounts of disadvantage in outcomes for individuals solely based on their memberships in a protected group. Utilizing tools from search-based software engineering and generative AI, we present a randomized algorithm that samples a statistically significant set of points from the tail of ML outcome distributions even if the input dataset lacks a sufficient number of relevant samples. We conducted several experiments on four ML models (deep neural networks, logistic regression, and random forests) over 10 socially relevant tasks from the literature on algorithmic fairness. First, we evaluate the generative AI methods and find that they generate sufficient samples to infer valid EVT distribution in 95% of cases. Remarkably, we found that the prevalent bias mitigators reduce the average-case discrimination but increase the worst-case discrimination significantly in 35% of cases. We also observed that even the tail-aware mitigation algorithm—MiniMax-Fairness—increased the worst-case discrimination in 30% of cases. We propose a novel ECD-based mitigator that improves fairness in the tail in 90% of cases with no degradation of the average-case discrimination. We hope that the EVT framework serves as a robust tool for evaluating fairness in both average-case and worst-case discrimination. 

Not AvailableMachine learning (ML) is increasingly used in high-stakes areas like autonomous driving, finance, and criminal justice. However, it often unintentionally perpetuates biases against marginalized groups. To address this, the software engineering community has developed fairness testing and debugging methods, establishing best practices for fair ML software. These practices focus on training model design, including the selection of sensitive and non-sensitive attributes and hyperparameter configuration. However, the application of these practices across different socio-economic and cultural contexts is challenging, as societal constraints vary. Our study proposes a search-based software engineering approach to evaluate the robustness of these fairness practices. We formulate these practices as the first-order logic properties and search for two neighborhood datasets where the practice satisfies in one dataset, but fail in the other one. Our key observation is that these practices should be general and robust to various uncertainty such as noise, faulty labeling, and demographic shifts. To generate datasets, we sift to the causal graph representations of datasets and apply perturbations over the causal graphs to generate neighborhood datasets. In this short paper, we show our methodology using an example of predicting risks in the car insurance application.