Analysing Guarantees in Australian Senate Outcomes

Abstract: Single Transferable Vote (STV) is used to elect candidates to the 76 seat Australian Senate across six states and two territories. These eight STV contests are counted using a combination of ballot scanners, manual data entry and tabulation software. On election night, some properties of the set of cast ballots are determined by hand. This includes the first preference tallies of each party. This technical report considers whether there are some properties, such as individual candidates' first preference tallies, that, if assumed to be accurate, imply a portion of the election outcome. The paper also presents an interesting example showing that the rules of STV tabulation used for the Australian Senate can allow bizarre behaviour, such as votes increasing in value over time.