The Australian Senate is composed of 76 members: twelve from each one of Australia's six states, and two from each of the country's two internal territories. Normally, one-half of the Senators from each state are elected every three years, along with all territory Senators, for a total of forty contested Senate seats on a half-Senate election. However, in the event the Senate repeatedly fails to approve legislation passed by the House of Representatives, the Constitution of Australia provides for the dissolution of both houses of Parliament - a double dissolution - followed by elections for the House of Representatives and the full Senate. Half-Senate elections may be held separately from House elections, but since 1970 no federal election has been held solely to fill half the Senate.

Senators are elected on a state/territory-wide basis by the Single Transferable Vote (STV) system, which combines proportional representation (PR) with preferential voting. Under the system in place prior to the 2016 electoral reform, voters cast a formal or valid ballot either by indicating a preference for a single ticket - a practice known as group ticket voting, where preferences were counted according to the official order of preferences registered with the Australian Electoral Commission by the party or group fielding the ticket - or by ranking all individual candidates in order of preference. Group ticket voting, introduced in 1984, was chosen by 95.2% of voters in the 2001 federal election.

A 2016 electoral system reform abolished group ticket voting and introduced optional preferential voting for Senate elections. Under the reformed system, voters are required to complete at least six preferences above the line, or at least twelve below the line.

In each state and territory, Senate seats are awarded to candidates who attain the state or territory quota, calculated by dividing the number of formal first preference votes cast in the state or territory by one more than the number of seats to be filled, and then adding one to the result. A candidate whose first preference vote totals equal or exceed the quota is immediately elected; if the candidate obtained more first preference votes than the quota, the surplus is distributed among the remaining candidates, in proportion to the second preferences of all votes cast for the successful candidate. The surplus transfer may result in the election of one or more candidates, in whose case the described procedure is repeated. However, if there are unallocated seats after transferring surplus votes from elected candidates, the candidate with the lowest number of votes is eliminated, and the preferences of the eliminated candidate are transferred to the remaining candidates. These two processes are repeated until all seats are filled, with surplus transfers taking precedence over the exclusion of unsuccessful candidates.

For example, in the 2001 federal election in the state of New South Wales, a total of 3,879,443 first preference votes were cast for sixty-five candidates contesting six Senate seats. Therefore, the quota was computed in the following manner:

Two candidates were elected in the first count: Helen Coonan of the Liberal/National Party joint ticket, with 1,615,798 votes; and Ursula Stephens of the Australian Labor Party (ALP), with 1,293,880 votes. Since the vote for both Coonan and Stephens exceeded the quota, their respective surpluses were distributed among the remaining candidates. Coonan's surplus of 1,061,591 votes was transferred at the following proportion or transfer value:

Then, Coonan's votes were re-examined to find the second preferences of her voters, which were distributed among the remaining candidates at the computed transfer value. Thus, if 1,613,237 of Coonan's voters chose Sandy MacDonald (also of the Liberal/National Party ticket) as their second preference, MacDonald received the following number of votes:

As a result, MacDonald was elected with 1,061,265 votes on the second count. On the third count, the ALP's George Campbell was elected with 741,098 votes after the transfer of Stephens' 739,673 surplus votes. MacDonald's surplus was distributed on the fourth count, while Campbell's was transferred on the fifth count, but no candidate reached the quota in either count. Therefore, the candidates with the smallest number of votes were successively eliminated, and the preferences of their voters were transferred to the remaining candidates, until Marise Payne of the Liberal/National Party was elected with 580,904 votes on the 226^th count. No candidate reached the quota upon the distribution of Payne's surplus on the 227^th count, so the exclusion of candidates with the lowest vote totals was resumed, with their voters' preferences transferred to the remaining candidates, until Kerry Nettle of the Australian Greens was elected for the sixth and final seat on the 240^th count, defeating Vicki Bourne of the Australian Democrats by 588,681 votes to 516,243.

It should be pointed out that the Australian Greens managed to capture one of New South Wales' Senate seats despite receiving fewer first preference votes than the Australian Democrats and Pauline Hanson's One Nation. This outcome underscores the importance of preference transfers between candidates, a distinct feature of STV that sets aside this system from other forms of proportional representation, which allocate seats according to the number of votes obtained by competing party lists.

Nonetheless, and despite the constitutional requirement of equal representation for six states with widely varying population sizes, the overall distribution of seats in the Senate is highly proportional. In contrast to the House of Representatives, neither the ALP nor the Liberal/National Coalition have held an absolute majority of Senate seats since 1981 (except from 2005 to 2008, when the Liberal/National Coalition attained a Senate majority after the forty Senators elected in 2004 took office). Consequently, STV has allowed minor groups - such as the Australian Democrats at one point in time - to not only gain Senate representation, but also attain a measure of influence over government policy by holding the balance of power in the upper house of Australia's Parliament.

Copyright © 2004-2018 Manuel Álvarez-Rivera. All Rights Reserved.
Last update: November 11, 2018.