Strategic Cost Selection in Participatory Budgeting

Piotr Faliszewski (AGH University of Science and Technology, Krakow, Poland) · Łukasz Janeczko (AGH University of Science and Technology) · Andrzej Kaczmarczyk (University of Chicago) · Grzegorz Lisowski (University of Groningen) · Piotr Skowron (University of Warsaw) · Stanisław Szufa (AGH University Poland) · Mateusz Szwagierczak (AGH University of Science and Technology)

approval-based budgetingav/cost rulecost selectionelection dataexperimental studyfixed votesgame theorymethod of equal sharesminimum costsparticipatory budgetingphragmen ruleproject pricingproject proposerspure nash equilibriaselection criteriastrategic behavior

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, Phragmen, and Method of Equal Shares rules. We also provide an experimental study of cost selection on real-life PB election data.