Proportional Participatory Budgeting




Since Participatory Budgeting (PB) has arisen as an interesting application of social choice,  I wanted to share one of our key papers on the topic. The paper was written in 2019 with Barton Lee and was published at AAAI 2021. It presents axioms for the problem of PB under ordinal preferences over projects. The input format of weak ordinal is more general and expressive than approval ballots that only allows voters to express a subset of projects. In particular, we propose a polynomial-time algorithm called PB-EAR that returns PB outcomes that satisfy a natural and desirable proportional representation axiom called Inclusion PSC (IPSC).

Publication Link: https://ojs.aaai.org/index.php/AAAI/article/view/16646

Slides and Presentation: https://slideslive.com/38948098/proportionally-representative-participatory-budgeting-with-ordinal-preferences

Paper Abstract:

Participatory budgeting (PB) is a democratic paradigm whereby voters decide on a set of projects to fund with  a limited budget. We consider PB in a setting where voters report ordinal preferences over projects and have (possibly) asymmetric weights. We propose proportional representation axioms and clarify how they fit into other preference aggregation settings, such as multi-winner voting and approval-based multi-winner voting. As a result of our study, we also discover a new solution concept for approval-based multi-winner voting, which we call Inclusion PSC (IPSC). IPSC is stronger than proportional justified representation (PJR), incomparable to extended justified representation (EJR), and yet compatible with EJR. The well-studied Proportional Approval Voting (PAV) rule produces a committee that satisfies both EJR and IPSC; however, both these axioms can  also be satisfied by an algorithm that runs in polynomial-time. 

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