Australia provides perhaps the longest-running demonstration of an “instant runoff” system. Since 1918, following the enactment of the Commonwealth Electoral Act of 1918, Australia has required voters to preferentially rank candidates for the Senate (§ 239) and for the House of Representatives (§ 240). As described in the Australian Electoral Commission’s online guide to Commonwealth electoral procedures (April 1999), “full preferential voting” applies to elections for both legislative bodies, even though the House consists of legislators elected from single-member districts (¶ 8.1) and the Senate consists of legislators elected from multiple-member districts (¶ 8.1). “Full preferential voting” means that “electors must indicate [on their ballots] a complete order of preference among a list of candidates” (¶ 8.2).

      For the House of Representatives, a straightforward “instant runoff” mechanism determines the victor in the single-member House districts. “Members of the House of Representatives are elected on the basis of an absolute majority system. The first preference votes recorded for each candidate are counted. If any candidate receives more than 50 per cent of the first preference votes, that candidate is immediately elected” (¶ 8.4; see also Appendix G). Otherwise, scrutiny of the ballots continues. “[T]he candidate who has received the fewest first preference votes is excluded and all the ballot papers held by that candidate are transferred to the continuing candidates according to the next available preference expressed on each ballot paper” (¶ 9.27). “[T]he process of excluding the candidate who has the fewest votes continues until only two candidates remain in the count” (¶ 9.27). “The candidate who, at any stage during the scrutiny, has an absolute majority (50 per cent plus one vote) of all formal votes is elected” (¶ 9.28).

      For the Senate, the multiple-member-district character of the election requires a modified “instant runoff” procedure (¶ 9.25; see also Appendix F).

      High rates of voter turnout in Australian federal elections might suggest that instant-runoff voting dramatically increases rates of voting. IRV might have that effect, but Australia’s experience does not actually justify conclusion. Why? Because Australia has compulsory voting. “Compulsory voting has applied at all federal elections since 1924. Voting is compulsory for all electors with the exception of eligible overseas electors, itinerant electors (see para 4.25) and Antarctic electors. Persons failing to vote at a federal election must provide a valid and sufficient reason or pay an administrative penalty of $20, or have the matter dealt with in court – in which case they may be fined up to $50 plus any court costs” (¶ 8.5). Consequently, if IRV increases voter turnout, the evidence of that effect will have to come from somewhere other than Australia.

      For some additional historical background on Australia’s IRV system, see the Australian Electoral Commission’s Election Backgrounder 7: Langer-style voting.