Risk-limiting Audits for Nonplurality Elections

Many organizations have turned to alternative voting systems such as instant-runoff voting for determining the outcome of single-winner elections. It is our position in this paper that the increasing deployment of such alternative systems necessitate the study and development of risklimiting audits for these systems. We initiate this study. We examine several commonly used single-winner voting systems and provide risk-limiting auditing procedures for them. In many cases the methods from auditing plurality contests can be applied with minor changes and little loss in efficiency. For instant-runoff voting (IRV), the situation is markedly different. We describe an algorithm for auditing the candidate elimination order using plurality methods which is risk-limiting. Standard risk-limiting methods can be employed if the margin of the election can be efficiently calculated or bounded. We provide efficiently computable upper and lower bounds on the margin and, when known, compare them to the exact margins. Both auditing algorithms are potentially far less efficient than the methods to audit other types of voting systems.