Percentage-Based versus Statistical-Power-Based Vote Tabulation Audits [View All]

[Wilms]

"Tiered percentage audits specify a percentage of precincts to be audited, depending on the reported winning margin."

"This approach addresses the need to audit more when margins are narrower..."

"Statisticians and a growing number of election experts have urged replacing fixed percentage audits with audits that employ a statistically grounded criterion of efficacy. Here we present a power-based audit which determines the number of precincts that must be sampled to achieve a specified power level for each election contest. In addition to the desired power, the sample size will depend on the reported victory margin, the value ofWPM, and both the number and size-distribution of the precincts."

"Since a key purpose of a post-election vote tabulation audit is to provide a check on the original tabulations, procedures should verify election results without trusting any part of the software used in voting."

Percentage-Based versus Statistical-Power-Based Vote Tabulation Audits

Authors: McCarthy, John; Stanislevic, Howard; Lindeman, Mark; Ash, Arlene S.; Addona, Vittorio; Batcher, Mary
Source: The American Statistician, Volume 62, Number 1, February 2008 , pp. 11-16(6)
Publisher: American Statistical Association



Abstract:

Several pending federal and state electoral-integrity bills specify hand audits of 1% to 10% of all precincts.

However, percentage-based audits are usually inefficient, because they require large samples for large jurisdictions, even though the sample needed to achieve good accuracy is much more affected by the closeness of the contest than population size. Percentage-based audits can also be ineffective, since close contests may require auditing a large fraction of the total to provide confidence in the outcome.

We present a plausible statistical frame-work that we have used in advising state and local election officials and legislators. In recent federal elections, this audit model would have required approximately the same effort and resources as the less effective percentage-based audits now being considered.

http://www.ingentaconnect.com/content/asa/tas/2008/00000062/00000001/art00002


A free full text pdf version is available:
pdf: http://verifiedvoting.org/downloads/TAS_paper.pdf