PROVIDENCE: a Flexible Round-by-Round Risk-Limiting Audit

TL;DR

PROVIDENCE is a flexible, risk-limiting election audit method that balances efficiency and adaptability, proven to maintain rigorous error guarantees even under adversarial conditions, with practical implementation and planning tools.

Contribution

The paper introduces PROVIDENCE, a novel ballot polling RLA that combines efficiency and flexibility, with proven risk-limiting properties and practical planning tools.

Findings

PROVIDENCE outperforms existing RLAs in efficiency and flexibility.

Simulation results demonstrate PROVIDENCE's superiority in audit workload management.

Implementation in Rhode Island's 2021 election showcases practical applicability.

Abstract

A Risk-Limiting Audit (RLA) is a statistical election tabulation audit with a rigorous error guarantee. We present ballot polling RLA PROVIDENCE, an audit with the efficiency of MINERVA and flexibility of BRAVO. We prove that PROVIDENCE is risk-limiting in the presence of an adversary who can choose subsequent round sizes given knowledge of previous samples. We describe a measure of audit workload as a function of the number of rounds, precincts touched, and ballots drawn.We quantify the problem of obtaining a misleading audit sample when rounds are too small, demonstrating the importance of the resulting constraint on audit planning. We present simulation results demonstrating the superiority of PROVIDENCE using these measures and describing an approach to planning audit round schedules. We describe the use of PROVIDENCE by the Rhode Island Board of Elections in a tabulation audit of the 2021 election. Our implementation of PROVIDENCE and audit planning tools in the open source R2B2 library should be useful to the states of Georgia and Pennsylvania, which are planning pre-certification ballot polling RLAs for the 2022 general election.