Individual Arbitrariness and Group Fairness
Main Conference Track
Authors: Carol Long, Hsiang Hsu, Wael Alghamdi, Flavio Calmon

Machine learning tasks may admit multiple competing models that achieve similar performance yet produce conflicting outputs for individual samples---a phenomenon known as predictive multiplicity. We demonstrate that fairness interventions in machine learning optimized solely for group fairness and accuracy can exacerbate predictive multiplicity. Consequently, state-of-the-art fairness interventions can mask high predictive multiplicity behind favorable group fairness and accuracy metrics. We argue that a third axis of ``arbitrariness'' should be considered  when deploying models to aid decision-making in applications of individual-level impact.To address this challenge, we propose an ensemble  algorithm applicable to any fairness intervention that provably ensures  more consistent predictions.