DiffSum - A Simple Post-Election Risk-Limiting Audit

This paper presents DiffSum, a simple post-election risk-limiting ballot-polling audit for two-candidate plurality elections. DiffSum sequentially draws ballots (without replacement) until the numbers $a$, $b$, of votes for candidates $A$, $B$ satisfies $a>b$ and $(a-b)^2 > c(a+b)$, where $A$ is the reported winner and $c$ is a suitably chosen constant. Bounds on the error rate (chance of approving an incorrect election outcome) are obtained via simulations. The method is compared with the Bravo method of Lindeman, Stark, and Yates.