and Tideman (see: Counting Single Transferable Votes for further details). Australia Australia uses several forms of STV in different jurisdictions. The systems require voters to rank several, or all, of the candidates on the ballot, reducing or eliminating the possibility of exhausted votes. Lower house elections for the Australian parliament and for all states except Tasmania use what they call STV (what others call Instant-runoff voting to elect a single member for an electorate. In the Senate and most states, upper houses use proportional representation to elect multiple members for a state or district. The Hare-Clark system is used in Tasmania's House of Assembly and the Australian Capital Territory (ACT) Legislative Assembly. This is essentially the system described above using the Droop quota (not the Hare quota), but candidates' placements, within the column for each party, are randomised by Robson Rotation rather than alphabetical. Casual vacancies are filled by the countback method, which involves recounting the original ballots to elect one of the candidates who stood but failed to be elected in the last election. The Australian Senate and the upper houses of New South Wales, South Australia, Victoria and Western Australia use STV to elect multiple members with the option of voting "above the line". Queensland has a unicameral legislature — that is, it does not have an upper house. The Group Voting Ticket or Ticket-Voting system is in use in Victoria, and was used in the Senate from 1984 to 2013, in New South Wales from 1987 to 2003 and in South Australia from 1985 to 2018. Western Australia used it from 1987 until the 2021 election, but legislation has been introduced to abolish it. The votes are counted in the basically same way as under Hare-Clark, but when casting votes, voters have the option of selecting one single group "above the line", instead of numbering individual candidates below the line. Groups of candidates (usually, but not inevitably, corresponding to political parties) may each pre-register one ranked list of all the candidates (or, in some systems, two lists) and the votes above the line for each ticket are deemed to have numbered the candidates in the order pre-specified on the team's list (if the team lodged two lists, 50% of the votes go to each version). Casual vacancies are usually filled by the house of parliament with the vacancy, though there may be a requirement by law or