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One for One, or All for All: Equilibria and Optimality of Collaboration in Federated Learning
Richard Phillips · Han Shao · Avrim Blum · Nika Haghtalab

Federated learning is highly studied as an approach to collaboration across large populations, however, little has been explored in how to coordinate resources to maintain such data collaborations over time. Inspired by game theoretic notions, this paper introduces a framework for incentive-aware learning and data sharing in federated learning. Our notions of stable and envy-free equilibria formalize notions of fairness and stability for self-interested agents. For example, in an envy-free equilibrium, no agent would wish to swap their sampling burden with any other agent and in a stable equilibrium, no agent would wish to unilaterally reduce their sampling burden. In addition to formalizing this framework, our contributions include characterizing the structural properties of such equilibria, proving when they exist, and showing how they can be computed. Furthermore, we show that, in the worst case, a $\Omega(\sqrt{k})$ gap exists between the sample-minimizing and equilibrium solutions across realistic learning models.