  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 reported result, continuing this process until
either they support the recorded result, or they fall back to a full manual
recount. For elections with digitised scanning and counting of ballots, a
comparison audit compares randomly selected digital ballots with their paper
versions. Discrepancies are referred to as errors, and are used to build
evidence against or in support of the recorded result. Risk-limiting audits for
first-past-the-post elections are well understood, and used in some US
elections. We define a number of approaches to ballot-polling and comparison
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 were
made in the tallying and distribution of votes).
