Method of Equal Shares with Bounded Overspending

TL;DR

This paper introduces BOS Equal Shares, a new participatory budgeting method that balances fairness and efficiency, backed by empirical results demonstrating its strong performance on real-world data.

Contribution

It proposes BOS Equal Shares, a novel variant of the Method of Equal Shares that improves fairness and efficiency in participatory budgeting.

Findings

BOS Equal Shares performs well across multiple metrics on real-world data.

The fractional variant allows partial funding, offering more flexibility.

The method balances proportionality with efficiency, addressing previous limitations.

Abstract

In participatory budgeting (PB), voters decide through voting which subset of projects to fund within a given budget. Proportionality in the context of PB is crucial to ensure equal treatment of all groups of voters. However, pure proportional rules can sometimes lead to suboptimal outcomes. We introduce the Method of Equal Shares with Bounded Overspending (BOS Equal Shares), a robust variant of Equal Shares that balances proportionality and efficiency. BOS Equal Shares addresses inefficiencies implied by strict proportionality axioms, yet the rule still provides fairness guarantees, similar to the original Method of Equal Shares. Our extensive empirical analysis on real-world PB instances shows excellent performance of BOS Equal Shares across several metrics. In the course of the analysis, we also present and examine a fractional variant of the Method of Equal Shares which allows for partial funding of projects.