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Sep 28, 2009

Election Simulation - ALP 101 Seats

Hot off the heels of today's Newspoll quarterly aggregation in the Oz, comes the Pollytics quarterly election simulation. The way it works for those never having seen it before, is we c

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Hot off the heels of today’s Newspoll quarterly aggregation in the Oz, comes the Pollytics quarterly election simulation. The way it works for those never having seen it before, is we combine the state breakdowns of both Newspoll and Nielsen over the past 3 months, weighted by sample size, to get a pooled estimate of the two party preferred for each State. That State estimate then gives us the state based swing since the last election for each state, whereby we then apply the relevant  State based swing to all 150 seats. However, we don’t just do it once (like happens with the election pendulum). We create a probability distribution for each seat where the mean swing is the state based swing, and where a standard deviation is applied that is a combination of the historical standard deviation of each state at Federal elections, as well as the standard deviation attached to the sampling error of the polling – the margin of error of the polling for each state.

We then then simulate 20,000 elections and tally up the results to get the most likely outcome were an election held in the last 3 months.

Were an election held, the ALP would have won 101 seats – a 1 seat gain since the June quarter. For the nerdy types, the distributions of the simulations – done in both “Seats in Parliament” and “Total Seats won/lost” – using the ALP come in like this:

seathist seatsim

seatsgainhist seatsgainedsim

The histograms (column charts) show the distribution of the simulations while the line charts are the results turned into a probability distribution, where you can simply choose an outcome from the bottom axis (either the ALP gaining X number os feats in Parliament, or the ALP gaining X number of seats from their current position), trace that outcome up until it intersects the red line, then trace that across to the vertical axis to show the implied probability of the ALP gaining at least that number of seats were an election held in the last three months.

We’ll be going over this quarterly Newspoll for a few days, and we’ll change the demographics in the sidebar (which is a combo of both Nielsen and Newspoll data) today or tomorrow – but in the meantime, it’s worth looking at the estimated change in voting intention since the last election, by geography, using this latest Newspoll.

alpprimsep09 lnpprimsep09

greenprimsep09 alptppsep09

The Coalition are down across the board in every state and the capital cities, only holding their own in the regions. Labor have lost some primary vote in NSW (it went to the Greens on net), and a point thereabouts in the non-capital cities (again, to the Greens on net). Qld is steady, Vic is up slightly, while South Australia and WA are up strongly.

South Australia is a major problem for the Coalition – facing a swing of 8.6% against them since the last election. Christopher Pyne must be in deep, deep shit in Sturt with the two party preferred vote in WA (oops) SA going to Labor 61/39. WA has come to the ALP party 2 and a half years later than everyone else, with Rudd pulling his highest ever primary vote in WA of 43% compared to the Libs 41%, washing out into an ALP two party preferred of 54/46 – again, the highest ever under the Rudd leadership of the ALP. In fact, the ALP has only ever achieved a primary of 43% in WA once before in the history of the Newspoll quarterly results – back in the 4th quarter of 1999.

Possum Comitatus — Editor of Pollytics

Possum Comitatus

Editor of Pollytics

Political Commentator and Blogger

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