Compilation and communication protocols for voting rules with a dynamic set of candidates (original) (raw)

The Complexity of Multiwinner Voting Rules with Variable Number of Winners

arXiv (Cornell University), 2017

We consider the approval-based model of elections, and undertake a computational study of voting rules which select committees whose size is not predetermined. While voting rules that output committees with a predetermined number of winning candidates are quite well studied, the study of elections with variable number of winners has only recently been initiated by Kilgour [18]. This paper aims at achieving a better understanding of these rules, their computational complexity, and on scenarios for which they might be applicable.

On Concept Lattices of Efficiently Solvable Voting Protocols

2006

It is shown that concept lattices can be attached in a natural way to any voting protocol. The concept lattices of some voting protocols that are solvable with respect to some prominnent solution concepts and outcome-efficient are studied: it is proved that they typically amount to chains

An efficient protocol for voting in distributed systems

[1992] Proceedings of the 12th International Conference on Distributed Computing Systems

In. distributed systems, data can be replicated to improve availability and performance. Many algorithms have been proposed to coordinate access to replicated data. Most of these algorithms require that the site initiating an operation on replicated data must communicate with all the other sites in the system. This results in high communication overheads. We propose II voting protocol, which can reduce the communication costs significantly. In the proposed scheme, the nodes are arranged an small intersecting groups, such that a site, in absence of failures, needs to communicate only with members of its group to collect the quorum. We suggest a method for constructing such logical groups and show that the message overhead of any operation in a system of N nodes is O(fi), when there are no or f e w failures in the system. We compare the availabili t y and the communication overheads of our protocol roilh those of the existin,g ones.

Single Transferable Vote: Incomplete Knowledge and Communication Issues

2019

Single Transferable Vote (STV) is used in large political elections around the world. It is easy to understand and has desirable normative properties such as clone-proofness. However, voters need to report full rankings, which can make it less practical than plurality voting. We study ways to minimize the amount of communication required to use single-winner STV. In the first part of the paper, voters are assumed to report their top-k alternatives in a single shot. We empirically evaluate the extent to which STV with truncated ballots approximates STV with full information. We also study the computational complexity of the possible winner problem for top-k ballots. For k=1k=1k=1, it can be solved in polynomial time, but is NP-complete when kgeq2k\geq 2kgeq2. In the second part, we consider interactive communication protocols for STV. Building on a protocol proposed by Conitzer and Sandholm (2005), we show how we can reduce the amount of communication required in practice. We then study empirica...

On Some Incompatible Properties of Voting Schemes

Lecture Notes in Computer Science, 2010

In this paper, we study the problem of simultaneously achieving several security properties, for voting schemes, without non-standard assumptions. This paper is a work in progress. More specifically, we focus on the universal verifiability of the computation of the tally, on the unconditional privacy/anonymity of the votes, and on the receipt-freeness properties. More precisely, under usual assumptions and efficiency requirements, we show that we cannot achieve:-universal verifiability of the tally (UV) and unconditional privacy of the votes (UP) simultaneously, unless all the registered voters actually vote;-universal verifiability of the tally (UV) and receipt-freeness (RF), unless the voting process involves interactions between several voters (and possibly the voting authority).

The Communication Burden of Single Transferable Vote, in Practice

Lecture Notes in Computer Science, 2018

Single Transferable Vote (STV) is of particular interest for voting, for cognitive reasons (it is easy to understand) and normative reasons (it is clone-proof). However, assuming that voters have to report full rankings sometimes makes it highly unpractical. We study single-winner STV from the point of view of communication. In the first part of the paper, we assume that voters give, in a single shot, their top k alternatives; we define a version of STV that works for such k-truncated votes, and we evaluate empirically (on randomly generated profiles, and on real data) the extent to which it approximates the standard STV rule. In the second part of the paper, we start from the protocol used by Conitzer and Sandholm (2005) for assessing the communication complexity of STV. We give an improvement of it, and then we study empirically the average communication complexity of these protocols, based on the one hand on randomly generated profiles, and on the other hand on real data. We also first give a polynomial-time computable characterization of possible winners at each step of this protocol. Our conclusion is that STV needs, in practice, much less information than in the worst case.

The computational difficulty of manipulating an election

Social Choice and Welfare, 1989

We show how computational complexity might protect the integrity of social choice. We exhibit a voting rule that efficiently computes winners but is computationally resistant to strategic manipulation. It is NP-complete for a manipulative voter to determine how to exploit knowledge of the preferences of others. In contrast, many standard voting schemes can be manipulated with only polynomial computational effort. for stimulating discussions.

Dynamically consistent voting rules

Journal of Economic Theory, 2015

This paper studies families of social choice functions (SCF's), i.e. a collection of social choice functions {Φ A }, where the family is indexed by the option set of choices. These (sets of) functions arise in sequential choice problems where at each stage a set of options is given to a population of voters and a choice rule must aggregate stated preferences to generate an aggregate choice. In such settings, the aggregate decision-making process should reflect some form of consistency across choice problems. We characterize the class of (sequences of) SCF's that satisfy two properties: (i) strategy-proofness and (ii) a notion of dynamic consistency inspired by Sen's α from choice theory. When the aggregate choice is anonymous, this class turns out to be exactly the set of q-rules, i.e. rules in which the selected alternative is the most preferred alternative of the voter at the q-th N-tile of the population (where N is the set of voters). This nests median voter schemes when no phantom voters are admitted in the decision rule. Without anonymity we obtain a class that we call "vote-by-committee" rules, the name due to some similarities with a class of SCF's axiomatized in Barberá et al. (1991).

Multi-Winner Elections: Complexity of Manipulation, Control and Winner-Determination

2007

Although recent years have seen a surge of interest in the computational aspects of social choice, no attention has previously been devoted to elections with multiple winners, e.g., elections of an assembly or committee. In this paper, we fully characterize the worst-case complexity of manipulation and control in the context of four prominent multi-winner voting systems. Additionally, we show that several tailor-made multi-winner voting schemes are impractical, as it is N P-hard to select the winners in these schemes.