Fair Voting Outcomes with Impact and Novelty Compromises? Unraveling Biases in Electing Participatory Budgeting Winners (2405.05085v3)

Abstract: Participatory budgeting, as a paradigm for democratic innovations, engages citizens in the distribution of a public budget to projects, which they propose and vote for implementation. So far, voting algorithms have been proposed and studied in social choice literature to elect projects that are popular, while others prioritize on a proportional representation of voters' preferences, for instance, the rule of equal shares. However, the anticipated impact and novelty in the broader society by the winning projects, as selected by different algorithms, remains totally under-explored, lacking both a universal theory of impact for voting and a rigorous unifying framework for impact and novelty assessments. This paper tackles this grand challenge towards new axiomatic foundations for designing effective and fair voting methods. This is via new and striking insights derived from a large-scale analysis of biases over 345 real-world voting outcomes, characterized for the first time by a novel portfolio of impact and novelty metrics. We find strong causal evidence that equal shares comes with impact loss in several infrastructural projects of different cost levels that have been so far over-represented. However, it also comes with a novel, yet over-represented, impact gain in welfare, education and culture. We discuss broader implications of these results and how impact loss can be mitigated at the stage of campaign design and project ideation.

• The paper demonstrates that the equal shares method reallocates budgets, causing a 7% loss for public space projects and up to a 25% gain for welfare-related initiatives.
• It compares utilitarian greedy and equal shares methods across 345 participatory budgeting elections to assess their effects on project impact and novelty.
• The study highlights that strategic campaign design can mitigate emergent biases, promoting a more diverse and proportionate allocation of public funds.

Investigating the Impact of Voting Methods in Participatory Budgeting

Introduction to Participatory Budgeting

So, let's start with the basics. Participatory budgeting (PB) is a cool concept where citizens directly decide on the allocation of a portion of public funds. Imagine a bunch of neighbors coming together to decide how to spend city money on local projects like parks, schools, or road improvements. Sounds awesome, right? Well, making sure this process is fair and impactful gets a bit tricky, and that's where different voting methods come into play.

Voting Methods: Utilitarian Greedy vs. Equal Shares

The research compares two main types of voting aggregation methods: utilitarian greedy and equal shares.

• Utilitarian Greedy: This method chooses the most popular projects until the budget runs out. It's like saying, "let's pick the most favorites first."
• Equal Shares: This method aims for proportional representation, distributing the budget such that the maximum number of voters are satisfied, even if that means picking less popular but cheaper projects.

Why is This Study Important?

This paper dives into a large-scale analysis (345 PB elections, to be exact) to understand if and how the different voting methods impact the types of projects that get funded. The researchers look at various project categories—public transit, urban greenery, education, welfare, etc.—to see where the money ends up.

Key Findings

Impact Loss and Gain with Equal Shares

1. Infrastructure and Sustainability Projects:
   • Impact Loss: Equal shares tend to disadvantage higher-cost projects related to infrastructure and sustainability like public transit and urban greenery. For example, they found the highest mean loss of budget share for public space projects at 7%.
   • Impact Gain: Conversely, it favors welfare, education, and cultural projects. These categories saw a net impact gain, with cost representation gains up to 25% for welfare projects.
2. Novelty in Projects:
   • Within-Impact-Area Novelty: Equal shares show a significant gain in novel projects (unique to this method) within certain impact areas like education and welfare.
   • Between-Impact-Areas Novelty: However, it shows a novelty loss in areas like urban greenery when considering the diversity of projects across all areas.
3. Proportional Representation:
   • Equal shares generally result in a more proportionate representation of different project types in the winning outcomes, reducing the over-representation seen in some areas like environmental protection under the utilitarian greedy method.
4. Cost Levels and Impact:
   • Equal shares show a varied impact depending on the cost level of the projects. For instance, very cheap projects related to urban greenery saw an impact loss, whereas very expensive educational projects had an impact gain in budget share and winning rate.

Practical Implications

For cities practicing participatory budgeting, these findings are crucial. They highlight the need for careful campaign design to strike a balance between fairness and impact. For example:

• Citizens: They get a better understanding of how their votes might shape outcomes—potentially encouraging more informed voting.
• Policymakers: Insights from this paper can help design PB sessions that better meet both sustainability goals and social welfare needs.
• Academics and Developers: New methodologies can be crafted to refine these voting processes further, addressing the highlighted biases and optimizing for both fairness and impact.

Real-World Case Studies

The paper also looked at real-world implementations in Aarau, Switzerland, and Wieliczka, Poland, where the equal shares method was used:

• Green Million Campaign (Wieliczka): Saw unexpected impact gains in public transit and urban greenery, diverging from the anticipated losses. This suggests that adjusting the campaign design to align with the aggregation method can indeed mitigate impact losses.
• City Idea Project (Aarau): Showed mixed results but highlighted the potential for substantial gains in project diversity and representation when awareness and strategic design are incorporated.

Conclusion

Voting methods in participatory budgeting are not just about fairness; they shape the society we live in by determining which projects get the green light. This paper shines a light on the nuanced effects of different voting methods, making a strong case for more thoughtful and informed participatory processes. As we move forward, such insights will be key in crafting better, more inclusive democratic innovations.