Efficient Computation of Exact IRV Margins
This work addresses a specific computational challenge in election auditing for IRV, offering a practical improvement over existing methods.
The paper tackles the problem of efficiently computing exact margins of victory for Instant Runoff Voting (IRV), which is crucial for verifying election outcomes and conducting risk-limiting audits. It presents a branch-and-bound algorithm that runs efficiently in practice on real examples and solves instances that previous state-of-the-art methods could not handle.
The margin of victory is easy to compute for many election schemes but difficult for Instant Runoff Voting (IRV). This is important because arguments about the correctness of an election outcome usually rely on the size of the electoral margin. For example, risk-limiting audits require a knowledge of the margin of victory in order to determine how much auditing is necessary. This paper presents a practical branch-and-bound algorithm for exact IRV margin computation that substantially improves on the current best-known approach. Although exponential in the worst case, our algorithm runs efficiently in practice on all the real examples we could find. We can efficiently discover exact margins on election instances that cannot be solved by the current state-of-the-art.