We are proud to announce that Colorado has chosen Free & Fair to build a risk-limiting audit (RLA) system to be used statewide beginning with the November 2017 general election. First developed in 2008, RLAs promote evidence-based confidence in election outcomes by comparing a random sampling of paper ballots to their corresponding digital versions. This will be the first time anywhere in the United States that risk-limiting audits are conducted on a regular, statewide basis. Free & Fair has already prototyped an open source risk-limiting audit tool called OpenRLA, for RLAs of election contests in single jurisdictions. The production RLA system being developed for Colorado will facilitate statewide, multi-county and individual county audits. Like OpenRLA, the RLA system developed for Colorado will be released under an open source license (GPL Version 3). Risk-limiting audits provide strong statistical evidence that a jurisdiction’s voting system accurately interpreted and tabulated voter markings on paper ballots, with relatively little hand counting. The “risk limit” is the largest chance that an outcome-changing error in the initial tabulation will not be discovered and corrected in the audit. If the risk limit is 5% and the outcome wouldn’t match the result of a full, accurate count of the paper ballots, there is at least a 95% chance that the audit will correct the outcome.
The risk limit calculation is based on worst-case assumptions, so the actual chance of correcting a wrong outcome may be much larger than 95%, depending on how and why the outcome is wrong. Mathematically speaking, with a 5% risk limit, a risk-limiting audit reduces any uncertainty about the correctness of the tabulation outcome by a factor of 20. The risk limit is one of two factors which determine how many ballots must be checked. The lower the risk limit, the more ballots that must be checked. The other factor is the contest’s margin of victory.
To conduct a risk-limiting audit, paper ballots from a race to be audited are randomly selected and compared to their corresponding digital representations. If the margin of victory is large, the number of ballots that must be checked can be as low as dozens. But, if the margin of victory is small, a larger number of random ballots will have to be checked to provide sufficient statistical evidence that the digital count is sufficiently accurate. RLAs can sometimes lead to a complete hand count, but usually only if the margin is razor thin, or if the tabulation system is not functioning properly. RLAs are an efficient, transparent way to determine whether the computers have correctly counted the votes.