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New Electorate Margins

Under the South Australian Constitution, a redistribution must take place after each election. Using rules that apply nowhere else in Australia, the process takes account of voting patterns and attempts to ensure that if a 'group' (single party or coalition) receives more than half of the state wide two-party preferred vote, it should also be able to win a majority of the seats. This has become known as the 'fairness' criteria, and carries greater weight than either geography or community of interest in drawing boundaries.

The fairness provision was inserted after the 1989 election, when the Bannon Labor government was re-elected despite winning only 48% of the state-wide two-party preferred vote. Labor formed government after winning 22 seats, plus two Labor leaning Independents and one National against 22 seats for the Liberal Party. Lacking an overall majority, the government was forced to adopt the new procedures, and they were inserted in the Constitution by a referendum in 1991. They can only be amended by a further referendum.

There were three reasons why Labor won the 1989 election with a minority of the vote. First, good campaigns by sitting Labor MPs in marginal seats helped them withstand the general swing. Second, the swing was largest in safe Labor seats which stood little chance of being won by the Liberal Party. Third, the Liberal Party's vote was concentrated in safe rural seats, one of the reasons the Liberal Party had disliked one-vote one-value electoral laws when introduced by the Dunstan government in the 1970s.

The redistribution after the 2002 election was the fourth under the fairness provision. The attempt to produce fairness has increased the number of marginal seats compared to the situation prior to 1993. However, the rules have had perverse consequences. Sitting MPs in marginal seats who do well by resisting a state-wide trend find themselves punished in the redistribution that follows each election as their seat is carved up to meet the criteria for state-wide fairness. Areas with little geographic connection get drawn together into single seats simply to balance competing voting patters.

As an example, O'Halloran Hill is an extension of the Adelaide Hills and extends to the coast at Port Stanvac. It forms a clear geographic boundary along the southern edge of the Adelaide plain and originally marked out the southern edge of Adelaide. In the 1960s, new suburbs began to develop south of the hill. The area is geographically separate from the rest of Adelaide, a fact reflected in local government boundaries.

The areas to the immediate south of O'Halloran Hill are Labor voting and those just to the north Liberal voting. Under the fairness criteria, balancing voting patterns carries greater weight than geography, and the electorates of Bright and Mitchell cross the geographic divide of O'Halloran Hill simply to produce two marginal electorates, when any argument about community of interest would have drawn boundaries reflecting the local geography.

Similarly, former Liberal MP for Adelaide Dr Michael Armitage constantly found his electorate pushed hither and thither in redistributions simply to increase the Labor vote in his seat. Adelaide is bordered by strong Labor voting areas to its immediate north and west, and strong Liberal voting areas to the north-east. Every time the Electoral Districts Boundaries Commission has needed to try and balance state wide voting patterns, it has been easiest to engineer the result by tinkering with the boundaries of Adelaide.

The process has become even more arcane in recent years as the Commission has begun to take into account future population growth. For instance, the electorate of Bright is unchanged by the 2002 redistribution, but based on population growth predictions, the Commission has estimated the seat's margin will fall from 5.0% in 2002 to 4.6% in 2006.

The Electoral Districts Boundaries Commission publishes its final margin estimates for all seats. These estimates are based on changes to boundaries, population change, and are also all rounded up by 0.1%.

This creates a problem for the ABC in trying to run an election night website, as the ABC's predictive system is based on historic voting patterns, not projected patterns of population growth. For that reason, this site does not use the Boundaries Commission's estimated margins, as these do not correspond to the historical booth votes that drive the ABC's election computers.

In most seats, this makes little difference. The only seats where there is a significant difference between the ABC and Boundaries Commission estimates is in Port Adelaide, where the Commission's estimates of the voting patterns in the rapidly growing suburb of Mawson Lakes creates a discrepancy.

The Commission also pays no regard to seats held by independents and third parties. All seats in the Commission's report are allocated margins based on a notional contest between the Liberal and Labor Parties. For that reason, the EDBC does not provide meaningful estimated margins in Chaffey, Fisher, Hammond, Mitchell and Mount Gambier.

The following table sets out the margin in all seats at the 2002 election, the ABC's estimate of the new margin, along with the published margin provided by the Electoral Districts Boundaries Commission.

Existing and Estimated Margins for South Australian Electorates
New Boundaries
District 2002 Margin ABC Estimate EDBC Estimate
Adelaide ALP 1.0 ALP 0.6 ALP 1.1
Ashford ALP 3.7 ALP 3.7 ALP 3.8
Bragg LIB 19.6 LIB 19.6 LIB 19.7
Bright LIB 5.0 LIB 5.0 LIB 4.6
Chaffey NAT 14.0 v LIB NAT 14.0 v LIB n.a.
Cheltenham ALP 16.7 ALP 16.7 ALP 16.8
Colton ALP 4.6 ALP 3.6 ALP 4.1
Croydon ALP 19.1 ALP 19.1 ALP 19.1
Davenport LIB 11.5 LIB 11.6 LIB 11.7
Elder ALP 3.7 ALP 3.5 ALP 3.6
Enfield ALP 15.9 ALP 15.6 ALP 15.9
Finniss LIB 15.6 LIB 15.6 LIB 15.9
Fisher IND 12.1 v LIB IND 12.2 v LIB n.a.
Flinders LIB 28.4 LIB 27.3 LIB 26.8
Florey ALP 3.7 ALP 3.6 ALP 3.6
Frome LIB 11.5 LIB 11.5 LIB 11.5
Giles ALP 9.7 ALP 5.3 ALP 5.3
Goyder LIB 16.2 LIB 16.2 LIB 16.1
Hammond IND 2.1 v LIB IND 2.2 v LIB n.a.
Hartley LIB 1.3 LIB 2.1 LIB 2.1
Heysen LIB 9.4 LIB 9.6 LIB 9.9
Kaurna ALP 11.0 ALP 10.9 ALP 10.8
Kavel LIB 13.1 LIB 13.1 LIB 12.8
Lee ALP 7.0 ALP 9.5 ALP 9.7
Light LIB 2.8 LIB 2.3 LIB 2.6
Little Para
(Formerly Elizabeth)
ALP 7.2 ALP 7.2 ALP 7.1
Mackillop LIB 20.3 LIB 20.3 LIB 20.4
Mawson LIB 3.5 LIB 3.6 LIB 3.5
Mitchell GRN 4.7 (ALP v LIB) GRN 4.7 (ALP v LIB) n.a.
Morialta LIB 4.1 LIB 3.3 LIB 3.6
Morphett LIB 10.0 LIB 10.1 LIB 10.4
Mount Gambier IND 26.6 v LIB IND 26.7 v LIB n.a.
Napier ALP 14.3 ALP 14.3 ALP 14.2
Newland LIB 5.7 LIB 5.5 LIB 5.5
Norwood ALP 0.5 ALP 0.5 ALP 0.5
Playford ALP 13.1 ALP 13.0 ALP 13.1
Port Adelaide ALP 21.7 ALP 20.6 ALP 18.9
Ramsay ALP 20.2 ALP 20.7 ALP 20.8
Reynell ALP 6.6 ALP 5.8 ALP 6.0
Schubert LIB 13.1 LIB 13.7 LIB 13.6
Stuart LIB 1.3 LIB 2.1 LIB 2.3
Taylor ALP 17.7 ALP 17.7 ALP 17.9
Torrens ALP 7.2 ALP 8.4 ALP 8.4
Unley LIB 9.0 LIB 9.0 LIB 9.1
Waite LIB 12.0 LIB 12.0 LIB 12.1
West Torrens ALP 8.6 ALP 8.6 ALP 8.9
Wright ALP 3.2 ALP 3.2 ALP 3.2

Page Last Updated: 12 December 2005

Update By: Antony Green