A Bayesian Method for Auditing Elections
نویسندگان
چکیده
We propose an approach to post-election auditing based on Bayesian principles, and give experimental evidence for its efficiency and effectiveness. We call such an audit a “Bayes audit”. It aims to control the probability of miscertification (certifying a wrong election outcome). The miscertification probability is computed using a Bayesian model based on information gathered by the audit so far. A Bayes audit is a single-ballot audit method applicable to any voting system (e.g. plurality, approval, IRV, Borda, Schulze, etc.) as long as the number of ballot types is not too large. The method requires only the ability to randomly sample single ballots and the ability to compute the election outcome for a profile of ballots. A Bayes audit does not require the computation of a “margin of victory” in order to get started. Bayes audits are applicable both to ballot-polling audits, which work just from the paper ballots, and to comparison audits, which work by comparing the paper ballots to their electronic representations. The procedure is quite simple and can be described on a single page. The Bayes audit uses an efficient method (which may be based on the use of gamma variates or on Pólya’s Urn) for simulating a Bayesian posterior distribution on the tally of a profile of ballots. A Bayes audit is very similar to single-ballot risklimiting audits. However, since Bayes audits are based on different principles, the precise relationship between risk-limiting audits and Bayes audits remains open. We provide some initial experimental results indicating that Bayes audits are quite efficient, requiring few ballots to be examined, and that the miscertification rate is indeed kept small, even for very close elections.
منابع مشابه
On Auditing Elections When Precincts Have Different Sizes
We address the problem of auditing an election when precincts may have different sizes. Prior work in this field has emphasized the simpler case when all precincts have the same size. Using auditing methods developed for use with equal-sized precincts can, however, be inefficient or result in loss of statistical confidence when applied to elections with variable-sized precincts. We survey, eval...
متن کاملRisk-limiting Audits and the Margin of Victory in Nonplurality Elections
Post-election audits are an important method for verifying the outcome of an election. Recent work on risk-limiting, post-election audits has focused almost exclusively on plurality elections. Several organization and municipalities use nonplurality methods such as range voting, the Borda count, and instantrunoff voting (IRV). We believe that it is crucial to develop effective methods of perfor...
متن کاملAuditing Australian Senate Ballots
We explain why the AEC should perform an audit of the paper Senate ballots against the published preference data files. We suggest four different post-election audit methods appropriate for Australian Senate elections. We have developed prototype code for all of them and tested it on preference data from the 2016 election. Authors are grouped by institution, in alphabetical order, and then list...
متن کاملVIGRE Final Report: Election Auditing Simulations of Risk-Limiting Auditing Techniques and the Effects of Reducing Batch Size on the 2008 California House of Representatives Elections
متن کامل
Risk-limiting Audits for Nonplurality Elections
Many organizations have turned to alternative voting systems such as instant-runoff voting for determining the outcome of single-winner elections. It is our position in this paper that the increasing deployment of such alternative systems necessitate the study and development of risklimiting audits for these systems. We initiate this study. We examine several commonly used single-winner voting ...
متن کامل