Minimizing Inequity in Facility Location Games

TL;DR

This paper introduces strategyproof mechanisms for facility location games on the real line that minimize group-level inequity, unifying classical and fairness-aware objectives with tight approximation guarantees.

Contribution

It proposes novel strategyproof mechanisms for single and multiple facilities that optimize fairness objectives, closing gaps in approximation bounds and unifying existing mechanisms.

Findings

Mechanisms are strategyproof and achieve tight approximation guarantees.

Unified framework encompasses classical and fairness-aware objectives.

Extended endpoint mechanism provides tight bounds for two-facility case.

Abstract

This paper studies the problem of minimizing group-level inequity in facility location games on the real line, where agents belong to different groups and may act strategically. We explore a fairness-oriented objective that minimizes the maximum group effect introduced by Marsh and Schilling (1994). Each group's effect is defined as its total or maximum distance to the nearest facility, weighted by group-specific factors. We show that this formulation generalizes several prominent optimization objectives, including the classical utilitarian (social cost) and egalitarian (maximum cost) objectives, as well as two group-fair objectives, maximum total and average group cost. In order to minimize the maximum group effect, we first propose two novel mechanisms for the single-facility case, the BALANCED mechanism and the MAJOR-PHANTOM mechanism. Both are strategyproof and achieve tight approximation guarantees under distinct formulations of the maximum group effect objective. Our mechanisms not only close the existing gap in approximation bounds for group-fairness objectives identified by Zhou, Li, and Chan (2022), but also unify many classical truthful mechanisms within a broader fairness-aware framework. For the two-facility case, we revisit and extend the classical endpoint mechanism to our generalized setting and demonstrate that it provides tight bounds for two distinct maximum group effect objectives.