Long-Term Fairness with Unknown Dynamics
This work addresses fairness in machine learning for populations over time, though it is incremental as it builds on existing online learning methods.
The paper tackles the problem of achieving long-term fairness in online reinforcement learning by formalizing dynamic control objectives that drive equity in population states, and demonstrates that their algorithm achieves probabilistic bounds on cumulative loss and fairness violations while adapting to unknown dynamics.
While machine learning can myopically reinforce social inequalities, it may also be used to dynamically seek equitable outcomes. In this paper, we formalize long-term fairness in the context of online reinforcement learning. This formulation can accommodate dynamical control objectives, such as driving equity inherent in the state of a population, that cannot be incorporated into static formulations of fairness. We demonstrate that this framing allows an algorithm to adapt to unknown dynamics by sacrificing short-term incentives to drive a classifier-population system towards more desirable equilibria. For the proposed setting, we develop an algorithm that adapts recent work in online learning. We prove that this algorithm achieves simultaneous probabilistic bounds on cumulative loss and cumulative violations of fairness (as statistical regularities between demographic groups). We compare our proposed algorithm to the repeated retraining of myopic classifiers, as a baseline, and to a deep reinforcement learning algorithm that lacks safety guarantees. Our experiments model human populations according to evolutionary game theory and integrate real-world datasets.