The Mackerras pendulum as a way of predicting the outcome of an election contested between two major parties in a Westminster style lower house legislature such as the Australian House of Representatives, which is composed of single-member electorates and which uses a preferential voting system such as a Condorcet method or instant-runoff voting.

The pendulum works by lining up all of the seats held in Parliament for the government, the opposition and the crossbenches according to the percentage point margin they are held by on a two party preferred basis. This is also known as the swing required for the seat to change hands. Given a uniform swing to the opposition or government parties, the number of seats that change hands can be predicted.

Government seats (82)MarginalChisholmVicHelen MayerALP0.2RankinQldDavid BeddallALP0.6DunkleyVicBob ChynowethALP1.1BartonNSWGary PunchALP1.2BallaratVicJohn MildrenALP1.5Eden-MonaroNSWJim SnowALP2.0BendigoVicJohn BrumbyALP2.0McEwenVicPeter CleelandALP2.1LoweNSWMichael MaherALP2.2HunterNSWEric FitzgibbonALP2.4StirlingWARon EdwardsALP2.5BurkeVicNeil O'KeefeALP2.9StreetonVicTony LambALP3.3HawkerSARalph JacobiALP3.4HerbertQldTed LindsayALP3.6CanningWAGeorge GearALP3.8CowanWACarolyn JakobsenALP4.0PhillipNSWJeannette McHughALP4.2CapricorniaQldKeith WrightALP4.2BrisbaneQldManfred CrossALP4.3IsaacsVicDavid CharlesALP4.4MakinSAPeter DuncanALP4.4MooreWAAllen BlanchardALP5.1BowmanQldLen KeoghALP5.3LeichhardtQldJohn GaylerALP5.5BrandWAWendy FatinALP5.5CalareNSWDavid SimmonsALP5.6LilleyQldElaine DarlingALP5.7KalgoorlieWAGraeme CampbellALP6.0Fairly safeJagajagaVicPeter StaplesALP6.1PerthWARic CharlesworthALP6.3HindmarshSAJohn ScottALP6.4HughesNSWRobert TicknerALP6.5St GeorgeNSWStephen DuboisALP6.5AstonVicJohn SaundersonALP6.5HentyVicJoan ChildALP6.7SwanWAKim BeazleyALP7.0GreySALloyd O'NeilALP7.1KingstonSAGordon BilneyALP7.4McMillanVicBarry CunninghamALP8.0HothamVicLewis KentALP8.2RobertsonNSWBarry CohenALP8.6La TrobeVicPeter MiltonALP8.7DobellNSWMichael LeeALP9.9AdelaideSAChris HurfordALP10.0SafeGriffithQldBen HumphreysALP10.3MaribyrnongVicAlan GriffithsALP10.4BanksNSWJohn MountfordALP11.4LindsayNSWRoss FreeALP11.6CanberraACTRos KellyALP11.6ParramattaNSWJohn BrownALP11.7ThrosbyNSWColin HollisALP11.7HoltVicMichael DuffyALP12.2MacarthurNSWStephen MartinALP12.3FraserACTJohn LangmoreALP12.3CorioVicGordon ScholesALP12.4OxleyQldBill HaydenALP13.0FremantleWAJohn DawkinsALP13.0ShortlandNSWPeter MorrisALP13.1GreenwayNSWRuss GormanALP13.8Melbourne PortsVicClyde HoldingALP14.2NewcastleNSWAllan MorrisALP14.5GrayndlerNSWLeo McLeayALP14.9BlaxlandNSWPaul KeatingALP16.2WerriwaNSWJohn KerinALP16.9CharltonNSWBob BrownALP17.3ReidNSWTom UrenALP17.3Port AdelaideSAMick YoungALP17.8BonythonSANeal BlewittALP18.9CunninghamNSWStewart WestALP19.1ProspectNSWDick KlugmanALP19.4ChifleyNSWRoger PriceALP19.5LalorVicBarry JonesALP20.0MelbourneVicGerry HandALP20.0Very safeFowlerNSWTed GraceALP20.3WillsVicBob HawkeALP20.3Kingsford SmithNSWLionel BowenALP20.9CalwellVicAndrew TheophanousALP22.2GellibrandVicRalph WillisALP23.3SydneyNSWPeter BaldwinALP23.4BatmanVicBrian HoweALP24.7ScullinVicHarry Jenkins Sr.ALP27.6 Opposition seats (66)MarginalFordeQldDavid WatsonLIB0.02HinklerQldBryan ConquestNAT0.2CaseyVicBob HalversonLIB0.6PetrieQldJohn HodgesLIB0.6DeakinVicJulian BealeLIB0.7DenisonTasMichael HodgmanLIB1.0GilmoreNSWJohn SharpNAT1.2FlindersVicPeter ReithLIB1.2LyonsTasMax BurrLIB1.3MacquarieNSWAlasdair WebsterLIB1.4Northern TerritoryNTPaul EveringhamCLP1.4BruceVicKen AldredLIB2.1FisherQldPeter SlipperNAT2.3ForrestWAPeter DrummondLIB2.4MoretonQldDon CameronLIB3.3CorangamiteVicStewart McArthurLIB3.4DawsonQldRay BraithwaiteNAT3.8CowperNSWGarry NehlNAT4.1BassTasWarwick SmithLIB4.4New EnglandNSWIan SinclairNAT4.6Riverina-DarlingNSWNoel HicksNAT4.6BraddonTasChris MilesLIB4.6FaddenQldDavid JullLIB4.7PageNSWIan RobinsonNAT5.1KennedyQldBob Katter Sr.NAT5.2CookNSWDon DobieLIB5.4FranklinTasBruce GoodluckLIB5.6MenziesVicNeil BrownLIB5.7SturtSAIan WilsonLIB6.0Fairly safeParkesNSWMichael CobbNAT6.1GoldsteinVicIan MacpheeLIB6.2WentworthNSWPeter ColemanLIB6.3LyneNSWBruce CowanNAT6.8RichmondNSWCharles BluntNAT7.2GwydirNSWRalph HuntNAT7.3HumeNSWWal FifeLIB7.7TangneyWAPeter ShackLIB7.8BennelongNSWJohn HowardLIB8.5DundasNSWPhilip RuddockLIB8.9BoothbySASteele HallLIB9.2CurtinWAAllan RocherLIB9.4MoncrieffQldKathy MartinLIB9.9SafeMackellarNSWJim CarltonLIB10.1RyanQldJohn MooreLIB10.4MayoSAAlexander DownerLIB10.5FairfaxQldEvan AdermannNAT10.6WarringahNSWMichael MacKellarLIB10.7North SydneyNSWJohn SpenderLIB11.0Wide BayQldClarrie MillarNAT11.8HigginsVicRoger ShiptonLIB12.1IndiVicEwen CameronLIB12.3BarkerSAJames PorterLIB12.6WakefieldSANeil AndrewLIB12.9FarrerNSWTim FischerNAT13.0KooyongVicAndrew PeacockLIB13.0McPhersonQldPeter WhiteLIB13.5GippslandVicPeter McGauranNAT14.3BerowraNSWHarry EdwardsLIB14.8WannonVicDavid HawkerLIB15.4MaranoaQldIan CameronNAT15.5GroomQldTom McVeighNAT15.9O'ConnorWAWilson TuckeyLIB19.2Very safeMitchellNSWAlan CadmanLIB20.8MalleeVicPeter FisherNAT21.4MurrayVicBruce LloydNAT23.1BradfieldNSWDavid ConnollyLIB25.5

References