QLD, TAS & NT federal redistributions – estimates of margins

In recent months, federal redistributions have been completed for Tasmania, the Northern Territory and Queensland, with Queensland’s being finalised on January 5.

As far as I can tell, no-one else has published margin estimates for the five Tasmanian seats and the two NT seats. Antony Green has published his estimates of the Queensland margins here. You’ll see that my estimates don’t diverge by much – by 0.1% per seat on average.

I have recently been calculating my own redistribution margins as part of the process of transferring booths so that I can produce maps for the new boundaries as part of my guides. This time I decided to use a new methodology which should be more reliable and quicker.

The AEC publishes data on how many votes were cast at each polling place (and each method of special vote) from each SA1 – the smallest area used for Census data. The AEC also publishes a list of every SA1 and which electorate it has been moved into (and out of) for each redistribution.

Using these datasets, it’s possible to quickly take the results of each booth, split them up in proportion to how much of that booth’s voters have been redistributed, and calculate new totals.

This is superior to my old methodology, where I would move booths according to which seat they lie in. Unfortunately this did not take account of small shifts where no booth moved, or where a booth was right on the border. I would have to guess how much of the booth’s voters would’ve shifted. The new method uses the actual AEC data. It is also a better solution to moving special votes. I’ve traditionally taken an even proportion of all special votes, even though this includes a bunch of pre-poll booths which are distributed across a seat. In practice these pre-poll booths would likely take more voters from one area than another, so distributing their votes according to the actual homes of the voters is far superior.

As to the results of these redistributions, 12 Queensland electorates experienced no change at all. Not one of the 37 seats has changed party. The biggest change has taken place in Lyons, with the Labor margin strengthened from 2.3% to 3.8%. The second biggest effect was in Blair, where the Labor margin was cut from 8.9% to 8.1%.

The five most marginal seats in these three jurisdictions did not experience any change. There was no boundary change in Flynn, Longman, Forde or Herbert, and the minor change to Capricornia had no impact on the seat’s margin.

The full list of margins are below the fold. I look forward to using this new method to quickly calculate margins for the three remaining redistributions (Victoria, SA and ACT) when the draft boundaries are released in coming months.

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