The above is from last federal election and can safely be ignored
A brief explanation.
In Australia we have single-member electorates in the House of Representatives (Lower House). In the Senate (Upper House) we have a reasonably complicated system of proportional representation.
The government of the day is determined in the Lower House by the numbers of these single-member electorates. Whoever gets most of these wins government.
The United Kingdom also has two houses, with government determined in the House of Commons, the Lower House. Like Australia it contains single-member electorates, but the voting system is a simple one of "First Past the Post". People have one vote and they cast it; whichever candidate gets the most votes wins, end of story. This is simple, but bad for voters who have to choose between more than one candidate of similar ideology.
In France they also have single-member electorates, but with run-offs, so that a week or so after the first poll, two (usually leading) candidates fight it out in another election.
Australia has much like the French system, but we do it all on the same day, on the same ballot paper. We tell the Electoral Commission who we would like to win in our seat. They get a number '1'. Then we say, if that person doesn't win, we'd like this person to win (number '2') and so on, until all boxes are filled.
The candidate you give a number one to has received your Primary Vote. At the end of the day all the primary votes are counted, and the candidate who received the least number of primary votes is eliminated from the contest. However, these ballot slips are not thrown away. They are again looked at to see who the voter put a number 2 next to, and added to that candidate's vote. Now the numbers of the remaining candidates votes are again examined, and the one with the least votes is eliminated, with their vote distributed as above.
This continues until there are only two candidates remaining. Whoever gets the most votes after distribution of all preferences wins. This is also called the two candidate preferred vote.
Of course, these days the Electoral Commission is smart enough to, when counting, physically register all the information on the ballot slip in one go, so they don't have to keep going back to each ballot slip to see where the next preference goes.
Another way of looking at is by making two piles of ballot slips, those
Preferential voting was introduced in Australia in 1919 by the
At the national level, the aggregate of all 150 seats translates into primary votes (of less importance - read more) and two-party preferred, which, as we've seen, is how a person wins an individual seat. The Labor figure and the Coalition figure add up to 100%, as between them they account for all the votes.
In a perfect world, the party with the most two party preferred votes would always win the greatest number of seats. As the graph shows, this ain't always necessarily so because voting is not uniform across electorates.
Go to the Electoral Commission's explanation of various systems
The directing of preferences is often greatly misunderstood. Parties and candidates can't choose where their preferences go in the House of Representatives. Voters must choose this on the ballot slip. They must "number every square".
Having said that, the parties "advise" with how to vote cards, and there is much evidence that people follow these with some obedience.
Preferences are of course highly important. If you vote one the Grey Bunjee-Jumping-Whale-Lovers and then two for the Liberal Party, it is, for all purposes, the same as voting one for the Liberal Party (assuming that the GBJWL hasn't a hope of winning). Yet people under-estimate this. When someone says they've had enough of both parties and are voting for someone else, the unavoidable fact, given the laws, is that you must in the end vote for one major party or the other.
The rare exception to this is when someone other than the main parties (Labor, Liberal (or LCP) or National) is included in the final two-candidate preferred count - when a minor party or independent comes first or second.
This happened at the last election in Calare in NSW, where Independent Peter Andren came first, and Mayo in South Australia, where Democrat John Schumman came second.