Voting for the House uses what is called preferential voting. (Some localities in the US use a variation on preferential voting called instant run-off voting. There is a slight difference explained further below).
There are two basic ways that candidates get on the ballot for a house seat -- either by filing as independents or as candidates of a registered party. An independent needs to file a petition with a small number of signatures (100) and a deposit ($AUS 1000). A registered party does not need signatures for each candidate (as it takes 500 members to become a registered party) but does need to make a deposit for each candidate. The deposit is refundable if the party/candidate gets enough votes. Needless to say, the deposit is not a big deal for the major parties which will get back their deposits in almost every division, but is significant for a new marginal party.
In the 2013 elections, four "parties" are running in every division. The two major parties in Australia are the Australian Labor Party and the "Coalition." The Labor Party is actually two parties -- running as Country Labor in 4 divisions. The Coalition is actually four parties -- and is the product of a working agreement between the Liberal Party and the National Party. In most of the country, the Liberal Party tends to be the urban and suburban center-right party with the National Party being a more rural party. For the most part, the Liberal Party and the National Party do not run against each other in Divisions and run a unified Senate ticket (the primary exception being Western Australia where the National Party runs its own Senate slate). In the Northern Territory, the Liberals run as the Country Liberal Party and, in Queensland, the two parties have merged into one party -- the Liberal National Party.
With four parties contesting every division and a multitude of other parties contesting some divisions, the number of candidates per division ranges from five candidates to sixteen candidates. When given the House ballot, there is a blank or box besides each candidate for the voters to rank that candidate from one on down. (For the ballot to count, the voter must rank all candidates.) The initial count in each division is of the voter's top choice. (On election night, they also guess at which candidates will be the final two and estimate the two-candidate preferred vote. This estimate is a good guide as to who will ultimately win and allows the media to project who will form the government.) After all the votes are counted (and given the absentee voting system it takes some time to get all ballots in). The last placed candidate is eliminated and those votes are redistributed to their second choice. This process continues until there are only two candidates and the candidate with the most votes after the final redistribution is elected.
Preferential voting differs from instant run-off voting in that preferential voting does not instantly go to the top two candidates, but starts by eliminating the last place candidate. If the top two candidates have over 33.34% of the vote, the difference between these two systems is academic as there are not enough votes available to be redistributed to the third-placed candidate to allow that candidate to move into the top two, but in the case of a close three-way or four-way contest, it is possible for the candidate who was third in initial preferences to be elected in a preferential voting system.
The senate election uses a system called single-transferrable vote. In the Senate election, each party runs a block of at least two candidates (independents can also form a block of candidates). As in the House, independent candidates need a petition signed by 100 voters. The deposit for Senate candidates is $AUS2000.
Each party or block can pre-file a list of preferences (or multiple list). If a party files such a list, a voter can adopt the list by voting for that party above the line. Alternatively, a voter can go to the list of individual candidates below the line and rank each of the candidates. (Not surprisingly, most voters choose to vote above the line.) With six slots in the state, it takes 14.3% to be elected (33.34% in the territories). Single transferrable vote is a cross between preferential voting and proportionate representation. If a party meets the "quota" to be elected, that quota is deducted from their votes and their top candidate is elected. This process continues until all six slots have been filed (unlikely) or until all parties are beneath the quota. At that point, the process becomes like preferential voting with the bottom parties/candidates eliminated and that party's votes redistributed according to the preference list. Given the complexity of this system, the calculation of who wins is done entirely by computer.
The advantage of both systems is that it allows voters to express their true preference without fear of wasting a vote. If your candidate finishes fourth or your party only gets 3% of the Senate vote, your vote gets transferred to your preferred major party candidate so you still get to have a say in the balance of power between Labor and the Coalition. Admittedly in over 130 of the divisions, the final two candidates will be Labor vs. the Coalition, and in most states at least five of the Senate seats will go to the major parties, but the initial vote allows the 20% who prefer some other party to indicate which party best reflects their preferred policies.
As noted above, key to this system and to the broad rules on absentee voting that I will discuss in future posts is the fact that each voter is only voting in two (or in this year's election, three elections). This allows separate ballot papers for each election and reduces the complexity of what is a very complex election system to manageable proportion. In a state that puts county and state elections on the same ballot as federal elections (the norm in the U.S.), it would be very difficult to use preferential voting.