Programme

Antoinette Baujard (Saint-Etienne)

Majority vs. Inclusion: Contrasting Two Rationales for Voting Rules

Different voting rules are conducive to different voting outcomes and different forms of electoral democracy (e.g. Riker 1982, Baujard et al. 2014, 2018), leaving the choice of a voting rule open (e.g. Patty and Penn 2014). Some historical and philosophical insights, which discuss the source of authority in a community, of the principle of majority, legitimacy or the importance of citizens involvement (e.g. Giercke 1913, Urfalino 2021), provide arguments to justify why a voting rule should be selected among many, some which stand in favor of the majority principle, but not only. This paper claims that two rationales should be distinguished to justify the choice of a voting rule: the majority principle, and the inclusion principle. This paper intends to propose experimental evidences for this distinction, based on in situ data collected during every French presidential election since 2007. It associates some rules with some properties and characteristics for each of these rationales. Last but not least, it supports a classification contrasting the majoritarian rules — including plurality rule and majority judgement — vs. inclusive voting rules — including evaluative and approval voting. In so doing, the paper illustrates how an experimental protocol can be designed to uncover and investigate issues of political philosophy.

Federica Ceron (Saint-Etienne)

Voice and Choice: An Axiomatic Approach to Ballot Information

The axiomatic approach in social choice theory aims at elucidating how well competing voting methods perform against a number of normative criteria. An axiomatic study typically begins by specifying what kind of preference information voters are allowed to provide in a ballot (dichotomous, ordinal, cardinal, truncated...), and then studies how this information should be aggregated. This impedes comparison of voting rules that use different kinds of information, such as Approval voting (dichotomous), the Borda rule (ordinal), and Evaluative voting (cardinal). It also obscures whether the information type itself has normative relevance. I will discuss how to axiomatically study ballot information and aggregation rules simultaneously - and if this approach can teach us something about the fundamental divide between voice and choice.

Julian Chingoma (Amsterdam)

Proportionality in Complex Domains

Proportionality is a fairness notion that has been extensively studied in the context of apportionment and multiwinner voting. Recent strides have also been made in adapting proportionality to the richer setting of Participatory Budgeting (PB) where citizens decide on the public projects, each having a cost, that are to be chosen with respect to some budget. In light of the work done in PB, we explore the possibilities of introducing proportionality to other, more complex, settings. In this work, we deal with two such settings, where for each, we aim to define a reasonable proportionality axiom and then investigate whether certain rules designed for the setting satisfy this axiom. The first setting is that of Judgment Aggregation (JA), a general framework fitted with logical constraints that make it a challenging task to develop natural proportionality notions for it. The second setting that we look at is a slight generalisation of the approval-based multiwinner voting where instead of the committee seats being treated equally, each seat on the committee is now associated with some weight. This latter setting naturally models scenarios where specific seats, such as the seat held by the committee's chair, are of greater value, and thus have more weight, than ordinary committee seats.

Zoé Christoff (Groningen)

The Illusion of Majority in Social Networks

The popularity of an opinion in one's direct circles is not necessarily a good indicator of its popularity in one's entire community. For instance, when confronted with a majority of opposing opinions in one's circles, one might get the impression that they belong to a minority. From this perspective, network structures act as a sort of "sample distortion filter". However, the way a social network is wired also constrains how much distortion can actually occur. In this paper, we discuss which classes of networks allow for a majority of agents to be given the wrong impression about what the majority opinion is, that is, to be in a "majority illusion".  

This is joint work with Maaike Los and Davide Grossi.  

Federico Fioravanti (Amsterdam)

Group Identification Problems in Different Settings

Group identification Problems are introduced as the issue of classifying the members of a group in terms of the opinions of their potential members. This involves a set of agents N, each one having an opinion about which agents should be classified as belonging to a specific subset J. A Collective Identity Function (CIF) aggregates those opinions yielding the class of members deemed J. A social planner postulate axioms, intended to ensure fair and socially desirable outcomes, characterizing different CIFs. This problem is considered with a finite and an infinite set of agents, and when the opinions are fuzzy. 

Adrian Haret (Amsterdam)

The Wisdom of Interacting Crowds

Arguments that groups can be wise, i.e., that they can be trusted to find an objectively correct answer, date back to Condorcet and are often probabilistic in nature. However, work in this tradition often operates under somewhat idealized assumptions, e.g., that agents have no strategic considerations when casting a ballot, and that they do so independently of each other. Under the latter assumption agents are precluded from communicating with, or otherwise influencing, each other. In real life, of course, agents often debate and exchange information prior to taking a vote, or simply choose to free-ride on others' competence. Do the optimistic conclusions of Condorcet's celebrated result still hold when its main assumptions are relaxed? The talk will focus on current and ongoing work investigating the truth-tracking abilities of groups, when members of such groups take cues from their peers for how to vote, or whether to show up at all.

Frederik Van De Putte (Rotterdam)

The Problem of No Hands: Responsibility Voids in Collective Decisions

The problem of no hands concerns the existence of so-called responsibility voids: cases where a group makes a certain decision, yet no individual member of the group can be held responsible for this decision. Criteria-based collective decision procedures play a central role in philosophical debates on responsibility voids. In particular, the well-known discursive dilemma has been used to argue for the existence of these voids. But there is no consensus: others argue that no such voids exist in the discursive dilemma under the assumption that casting an untruthful opinion is eligible. We argue that, under this assumption, the procedure used in the discursive dilemma is indeed immune to responsibility voids, yet such voids can still arise for other criteria-based procedures. We provide two general characterizations of the conditions under which criteria-based collective decision procedures are immune to these voids. Our general characterizations are used to prove that responsibility voids are ruled out by criteria-based procedures involving an atomistic or monotonic decision function. In addition, we show that our results imply various other insights concerning the logic of responsibility voids. 

This is joint work with Hein Duijf, University of Utrecht.

Piotr Skowron (Warsaw)

Proportional Participatory Budgeting

We study voting rules for participatory budgeting, where a group of voters collectively decides which projects should be funded using a common budget. We allow the projects to have arbitrary costs, and the voters to have arbitrary additive valuations over the projects. We formulate an axiom (Extended Justified Representation, EJR) that guarantees proportional representation to groups of voters with common interests. We propose a simple and attractive voting rule called the Method of Equal Shares that satisfies this axiom for arbitrary costs and approval utilities, and that satisfies the axiom up to one project for arbitrary additive valuations. This method can be computed in polynomial time. We compare Equal Shares with the currently used methods based on data coming from real elections.

The following individuals will be presenting posters at the workshop:

• Femke Bekius (Nijmegen)

• Théo Delemazure (Paris-Dauphine)

• Raphael Gomes de Oliveira (Paris-Cergy)

• Rajarshi Ghosh (ESSEC Paris)

• Andrzej Kaczmarczyk (Kraków)

• Maaike Los (Groningen)

• Dimitris Michailidis (Amsterdam)

• Oliviero Nardi (Vienna)

• Adrianna Navarro (Saint-Etienne)

• Ariane Ravier (Paris-Dauphine)

• Šimon Schierreich (Prague)

• Stanisław Szufa (Kraków)

• Mayesha Tasnim (Amsterdam)