- 9:45 Welcome and introduction by local organisers
- 10:00 Davide Grossi– University of Groningen and University of Amsterdam, Netherlands
Title: Power in Liquid Democracy
Abstract: My talk focuses on the notion of power in voting systems that allow for transitive delegations.Building on the Banzhaf-Penrose power index, I will present an index that can quantify the influence of both voters and delegators, and characterise it axiomatically. Then, using this index, I will study the equilibrium problem in delegation games where agents’ utilities depend on their power in the system. The interesting insight, which we also explore via simulations, is that power-seeking behavior in equilibrium has a balancing effect on the number of delegations that agents are able to accrue. This is joint work with Yuzhe Zhang (University of Groningen).
- 10:30 Grammateia Kotsialou – London School of Economics, UK
Title: Incentivising Participation in Liquid Democracy with Breadth-First Delegation
Abstract: Liquid democracy allows members of an electorate to either directly vote over alternatives, or delegate their voting rights to someone they trust. Most of the liquid democracy literature and implementations allow each voter to nominate only one delegate per election. However, if that delegate abstains, the voting rights assigned to her are left unused. To minimise the number of unused delegations, it has been suggested that each voter should declare a personal ranking over voters she trusts. We show that even if personal rankings over voters are declared, the standard delegation method of liquid democracy remains problematic. More specifically, we show that when personal rankings over voters are declared, it could be undesirable to receive delegated voting rights, which is contrary to what liquid democracy fundamentally relies on. To solve this issue, we propose a new method to delegate voting rights in an election, called breadth-first delegation. Additionally, the proposed method prioritises assigning voting rights to individuals closely connected to the voters who delegate. This is joint work with Luke Riley.
- 11:00 Hugo Gilbert – Université Paris Dauphine, France
Title: Delegation Games in Liquid Democracy with Restricted Preferences
Abstract: Transitive delegations is one of the key features of liquid democracy: e.g., A delegates to B and B delegates to C leads to A indirectly delegates to C. Unfortunately, because voters’ preferences over delegates may be conflicting, this process may not converge. There may not even exist a stable state (also called equilibrium). Delegation games provide a formalism to investigate the stability of the delegation process in liquid democracy. The players of the game are the voters of the election, their strategies are their possible delegations or the act to vote by themselves, and each voter has preferences about the person representing them. Several existence or optimization problems can be defined on such games and different restrictions have been studied either by adding a social graph structure constraint, or by studying restricted preferences (e.g., single peaked preferences).In this presentation, I will focus on the impact of restricting preferences. We will see that various natural structures of preference guarantee the existence of an equilibrium and we will provide both tractability and hardness results for the problem of computing several equilibria with some desirable properties. The presentation will be mostly based on the following paper: Iterative Delegations in Liquid Democracy with Restricted Preferences. AAAI 2020: 1926-1933. Bruno Escoffier, Hugo Gilbert, Adèle Pass-Lanneau
- 11:30 Ulrike Schmidt-Kraepelin – TU Berlin, Germany
Title: Liquid Democracy with Ranked Delegations
Abstract: We consider a generalization of liquid democracy in which voters are allowed to specify multiple delegates, together with a rank-ordering among them. Inherently, this setting induces the need for delegation rules, i.e., functions taking as an input the delegation preferences and output a weight distribution over the voters. We focus on the axiomatic analysis of delegation rules. In particular, we give axiomatic characterizations of two delegation rules previously considered in the literature, propose a new delegation rule, and formalize axiomatic properties which have been suggested by practitioners.This is joint work with Markus Brill, Anne-Marie George, and Martin Lackner.
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- 14:00 Lirong Xia– Rensselaer Polytechnic Institute, USA
Title: Representative Proxy Voting
Abstract: We study a model of proxy voting where the candidates,voters, and proxies are all located on the real line, and in-stead of voting directly, each voter delegates its vote to the closest proxy. The goal is to find a set of proxies that is θ-representative, which entails that for any voter located anywhere on the line, its favorite candidate is within a distance θ of the favorite candidate of its closest proxy. This property guarantees a strong form of representation as the set of voters is not required to be fixed in advance, or even be finite. We show that for candidates located on a line, an optimal proxy arrangement can be computed in polynomial time. Moreover, we provide upper and lower bounds on the number of proxies required to form a θ-representative set, thus showing that a relatively small number of proxies is enough to capture the preferences of any set of voters. An additional beneficial property of a θ-representative proxy arrangement is that for strict-Condorcet voting rules, the outcome of proxyvoting is similarly close to the outcome of direct voting. Joint work with Elliot Anshelevich, Zack Fitzsimmons, and Rohit Vaish
14:30 Palash Dey – Indian Institute of Technology Kharagpur, India
Title: On Parameterized Complexity of Liquid Democracy- 14:30 Nimrod Talmon – Ben-Gurion University, Israel
Title: Fine-grained Liquid Democracy
Abstract: One of the appeals of liquid democracy is the fact that it allows for more voter expressiveness, as voters can choose between voting directly or delegating. The option of delegation, however, is rather coarse, in the sense that voters have to delegate their complete ballots. I will speak about some attempts at providing a more fine-grained liquid democracy, in which voters can delegate parts of their ballots; e.g., delegating ordinal decisions regarding pairs of candidates and delegating approval or cardinal decisions regarding individual candidates. - 15:00 Discussion