196 research outputs found
Computing the Margin of Victory in Preferential Parliamentary Elections
We show how to use automated computation of election margins to assess the
number of votes that would need to change in order to alter a parliamentary
outcome for single-member preferential electorates. In the context of
increasing automation of Australian electoral processes, and accusations of
deliberate interference in elections in Europe and the USA, this work forms the
basis of a rigorous statistical audit of the parliamentary election outcome.
Our example is the New South Wales Legislative Council election of 2015, but
the same process could be used for any similar parliament for which data was
available, such as the Australian House of Representatives given the proposed
automatic scanning of ballots
Public Evidence from Secret Ballots
Elections seem simple---aren't they just counting? But they have a unique,
challenging combination of security and privacy requirements. The stakes are
high; the context is adversarial; the electorate needs to be convinced that the
results are correct; and the secrecy of the ballot must be ensured. And they
have practical constraints: time is of the essence, and voting systems need to
be affordable and maintainable, and usable by voters, election officials, and
pollworkers. It is thus not surprising that voting is a rich research area
spanning theory, applied cryptography, practical systems analysis, usable
security, and statistics. Election integrity involves two key concepts:
convincing evidence that outcomes are correct and privacy, which amounts to
convincing assurance that there is no evidence about how any given person
voted. These are obviously in tension. We examine how current systems walk this
tightrope.Comment: To appear in E-Vote-Id '1
Are Condorcet and minimax voting systems the best?
For decades, the minimax voting system was well known to experts on voting
systems, but was not widely considered to be one of the best systems. But in
recent years, two important experts, Nicolaus Tideman and Andrew Myers, have
both recognized minimax as one of the best systems. I agree with that. This
paper presents my own reasons for preferring minimax. The paper explicitly
discusses about 20 systems, though over 50 are known to exist.Comment: 41 pages, no figures. The Introduction has been changed. Also fixed
some version 6 errors in referencing subsection numbers in section
Adaptively Weighted Audits of Instant-Runoff Voting Elections: AWAIRE
An election audit is risk-limiting if the audit limits (to a pre-specified
threshold) the chance that an erroneous electoral outcome will be certified.
Extant methods for auditing instant-runoff voting (IRV) elections are either
not risk-limiting or require cast vote records (CVRs), the voting system's
electronic record of the votes on each ballot. CVRs are not always available,
for instance, in jurisdictions that tabulate IRV contests manually.
We develop an RLA method (AWAIRE) that uses adaptively weighted averages of
test supermartingales to efficiently audit IRV elections when CVRs are not
available. The adaptive weighting 'learns' an efficient set of hypotheses to
test to confirm the election outcome. When accurate CVRs are available, AWAIRE
can use them to increase the efficiency to match the performance of existing
methods that require CVRs.
We provide an open-source prototype implementation that can handle elections
with up to six candidates. Simulations using data from real elections show that
AWAIRE is likely to be efficient in practice. We discuss how to extend the
computational approach to handle elections with more candidates.
Adaptively weighted averages of test supermartingales are a general tool,
useful beyond election audits to test collections of hypotheses sequentially
while rigorously controlling the familywise error rate.Comment: 16 pages, 3 figures, accepted for E-Vote-ID 202
A Smooth Transition from Powerlessness to Absolute Power
We study the phase transition of the coalitional manipulation problem for
generalized scoring rules. Previously it has been shown that, under some
conditions on the distribution of votes, if the number of manipulators is
, where is the number of voters, then the probability that a
random profile is manipulable by the coalition goes to zero as the number of
voters goes to infinity, whereas if the number of manipulators is
, then the probability that a random profile is manipulable
goes to one. Here we consider the critical window, where a coalition has size
, and we show that as goes from zero to infinity, the limiting
probability that a random profile is manipulable goes from zero to one in a
smooth fashion, i.e., there is a smooth phase transition between the two
regimes. This result analytically validates recent empirical results, and
suggests that deciding the coalitional manipulation problem may be of limited
computational hardness in practice.Comment: 22 pages; v2 contains minor changes and corrections; v3 contains
minor changes after comments of reviewer
Automatic Margin Computation for Risk-Limiting Audits
A risk-limiting audit is a statistical method to create confidence in the correctness of an election result by checking samples of paper ballots. In order to perform an audit, one usually needs to know what the election margin is, i.e., the number of votes that would need to be changed in order to change the election outcome.
In this paper, we present a fully automatic method for computing election margins. It is based on the program analysis technique of bounded model checking to analyse the implementation of the election function. The method can be applied to arbitrary election functions without understanding the actual computation of the election result or without even intuitively knowing how the election function works.
We have implemented our method based on the model checker CBMC; and we present a case study demonstrating that it can be applied to real-world elections
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