Ballot-Polling Risk Limiting Audits for IRV Elections

Abstract

Risk-limiting post election audits guarantee a high probability of correcting incorrect election results, independent of why the result was incorrect. Ballot-polling audits select ballots at random and interpret those ballots as evidence for and against the actual recorded result, continuing this process until either they support the recorded result, or they fall back to a full manual recount. Ballot-polling for first-past-the-post elections is well understood, and used in some US elections. We define a number of approaches to ballot-polling risk-limiting audits for Instant Runoff Voting (IRV) elections. We show that for almost all real elections we found, we can perform a risk-limiting audit by looking at only a small fraction of the total ballots (assuming no errors).