Participatory Budgeting with Project Groups

TL;DR

This paper explores a generalized participatory budgeting model with multiple group-specific budgets, analyzing its computational complexity and providing algorithms for special cases to enhance inclusivity in decision-making.

Contribution

It introduces a generalized PB model with group budgets, studies its complexity, and offers efficient algorithms for specific scenarios, advancing participatory budgeting methods.

Findings

The problem is generally computationally hard.

Efficient algorithms exist for special cases like few groups.

Approximation algorithms are also developed.

Abstract

We study a generalization of the standard approval-based model of participatory budgeting (PB), in which voters are providing approval ballots over a set of predefined projects and -- in addition to a global budget limit, there are several groupings of the projects, each group with its own budget limit. We study the computational complexity of identifying project bundles that maximize voter satisfaction while respecting all budget limits. We show that the problem is generally intractable and describe efficient exact algorithms for several special cases, including instances with only few groups and instances where the group structure is close to be hierarchical, as well as efficient approximation algorithms. Our results could allow, e.g., municipalities to hold richer PB processes that are thematically and geographically inclusive.