On estimating the size and confidence of a statistical audit
EVT'07 Proceedings of the USENIX Workshop on Accurate Electronic Voting Technology
Machine-assisted election auditing
EVT'07 Proceedings of the USENIX Workshop on Accurate Electronic Voting Technology
CAST: Canvass audits by sampling and testing
IEEE Transactions on Information Forensics and Security - Special issue on electronic voting
Election audits using a trinomial bound
IEEE Transactions on Information Forensics and Security - Special issue on electronic voting
Risk-limiting postelection audits: conservative P-values from common probability inequalities
IEEE Transactions on Information Forensics and Security - Special issue on electronic voting
EVT/WOTE'09 Proceedings of the 2009 conference on Electronic voting technology/workshop on trustworthy elections
Understanding the security properties of ballot-based verification techniques
EVT/WOTE'09 Proceedings of the 2009 conference on Electronic voting technology/workshop on trustworthy elections
Some consequences of paper fingerprinting for elections
EVT/WOTE'09 Proceedings of the 2009 conference on Electronic voting technology/workshop on trustworthy elections
Software support for software-independent auditing
EVT/WOTE'09 Proceedings of the 2009 conference on Electronic voting technology/workshop on trustworthy elections
Implementing risk-limiting post-election audits in California
EVT/WOTE'09 Proceedings of the 2009 conference on Electronic voting technology/workshop on trustworthy elections
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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, evaluate, and compare a variety of approaches to the variable-sized precinct auditing problem, including the SAFE method [11] which is based on theory developed for equal-sized precincts. We introduce new methods such as the negative-exponential method "NEGEXP" that select precincts independently for auditing with predetermined probabilities, and the "PPEBWR" method that uses a sequence of rounds to select precincts with replacement according to some predetermined probability distribution that may depend on error bounds for each precinct (hence the name PPEBWR: probability proportional to error bounds, with replacement), where the error bounds may depend on the sizes of the precincts, or on how the votes were cast in each precinct. We give experimental results showing that NEGEXP and PPEBWR can dramatically reduce (by a factor or two or three) the cost of auditing compared to methods such as SAFE that depend on the use of uniform sampling. Sampling so that larger precincts are audited with appropriately larger probability can yield large reductions in expected number of votes counted in an audit. We also present the optimal auditing strategy, which is nicely representable as a linear programming problem but only efficiently computable for small elections (fewer than a dozen precincts). We conclude with some recommendations for practice.