Stylish Risk-Limiting Audits in Practice

TL;DR

This paper presents an open-source Python implementation of risk-limiting audits that utilize contest-specific ballot card data to significantly reduce the number of ballots needing manual review, demonstrated on large U.S. elections.

Contribution

It introduces a practical, open-source tool for risk-limiting audits that leverages contest-specific ballot data to improve efficiency in real-world elections.

Findings

CSD-based RLAs reduced sample sizes to about 0.65% and 3.1% of total ballots in two large elections.

The method successfully audited all contests with minimal hand counting, including close races.

The software is demonstrated on elections with over 1.8 million voters.

Abstract

Risk-limiting audits (RLAs) can use information about which ballot cards contain which contests (card-style data, CSD) to ensure that each contest receives adequate scrutiny, without examining more cards than necessary. RLAs using CSD in this way can be substantially more efficient than RLAs that sample indiscriminately from all cast cards. We describe an open-source Python implementation of RLAs using CSD for the Hart InterCivic Verity voting system and the Dominion Democracy Suite(R) voting system. The software is demonstrated using all 181 contests in the 2020 general election and all 214 contests in the 2022 general election in Orange County, CA, USA, the fifth-largest election jurisdiction in the U.S., with over 1.8 million active voters. (Orange County uses the Hart Verity system.) To audit the 181 contests in 2020 to a risk limit of 5% without using CSD would have required a complete hand tally of all 3,094,308 cast ballot cards. With CSD, the estimated sample size is about 20,100 cards, 0.65% of the cards cast--including one tied contest that required a complete hand count. To audit the 214 contests in 2022 to a risk limit of 5% without using CSD would have required a complete hand tally of all 1,989,416 cast cards. With CSD, the estimated sample size is about 62,250 ballots, 3.1% of cards cast--including three contests with margins below 0.1% and 9 with margins below 0.5%.