Strategic Cost Selection in Participatory Budgeting

TL;DR

This paper analyzes strategic behavior of project proposers in participatory budgeting, examining equilibrium existence under various rules and conducting experiments on real data to understand strategic cost setting.

Contribution

It introduces a model for strategic cost selection in PB, studies equilibrium existence under different rules, and provides experimental insights with real election data.

Findings

Pure Nash equilibria may or may not exist depending on the rule.

Proposers tend to set costs strategically to influence project selection.

Experimental results reveal patterns of strategic behavior in real PB elections.

Abstract

We study strategic behavior of project proposers in the context of approval-based participatory budgeting (PB). In our model we assume that the votes are fixed and known and the proposers want to set as high project prices as possible, provided that their projects get selected and the prices are not below the minimum costs of their delivery. We study the existence of pure Nash equilibria (NE) in such games, focusing on the AV/Cost, Phragm\'en, and Method of Equal Shares rules. Furthermore, we report an experimental study of strategic cost selection on real-life PB election data.