Australia's unique poll
SYDNEY, Australia (CNN) -- When Australia's 13 million voters go to the polls on Saturday October 9, they will take part in a national election that has two special characteristics setting it apart from most others.
Voting in Australia is compulsory, with a modest fine slapped on those who don't cast their ballot.
As well, the nation uses a preferential majority system that gives considerable power to minor political parties in determining the final result.
Compulsory voting has been a feature of Australian federal elections since 1924.
Everyone on the electoral roll must vote, subject to some qualifications. For example, itinerants, people living overseas and expeditioners in the Antarctic territory administered by Australia don't have to vote. Nor do people serving a jail term of more than three years.
People who object to voting can make a case in writing to the returning officer. But ultimately their reasons can be tested in court.
Strictly speaking, the act of voting is not compulsory. It is enough for an elector to attend a polling booth, have his or her name marked off the list of voters, be issued with a ballot paper and then put the folded paper in the ballot box.
Because voting is secret, there is no compulsion for a voter to complete the ballot paper before folding it and putting it in the box.
Compulsory voting was introduced in Australia after voter turnout had fallen to as low as 47 percent in elections before 1924.
Another argument put forward by its proponents was that it would free up the political parties to concentrate on explaining their policies, rather than having to be concerned about getting people to come and vote.
Preferences come into play
Under the Australian preferential voting system, a successful candidate must receive an absolute majority (50 percent plus 1) of the total formal votes cast.
The system is used in elections for the federal lower House of Representatives, and in most state lower houses in Australia (Tasmania and the Australian Capital Territory are the exceptions).
Its main benefit is that the winner is the "most preferred" candidate among all voters in a single electorate.
It also allows people to support minor parties and independents without "wasting" their vote, because their preferences may decide the ultimate winner.
On the ballot paper, electors are required to show their first, second, third, and so on, choice of candidates, by placing "1," "2," "3," against the candidates' names.
If no candidate wins an absolute majority on election night -- before absentee, postal and pre-poll votes are counted -- then these "preferences" come into play.
The candidate with the lowest number of first preference votes is excluded. These votes are then distributed to the remaining candidates according to the second preference.
If there is still no absolute majority for one candidate, then the candidate with the second lowest number of first votes is excluded, and their preferences are distributed to the remaining candidates. The process of distributing preferences continues until one candidate has an absolute majority.
Neither of the two main political parties in Australia -- the governing Liberal Party (supported by its National Party allies in rural electorates) and the opposition Australian Labor Party -- is likely to achieve more than 50 percent of the primary vote in the 2004 election.
This means that minor parties such as the Greens and the Democrats can influence the final result in the way they direct their preferences.
In seeking to win a flow of preferences from these minor parties, the two main parties will sometimes adjust their policies to make themselves more attractive.
A third aspect of the 2004 Australian federal election is that it includes a vote for half of the upper house, or Senate, along with all 150 seats in the lower House of Representatives.