Using 3PP data to understand three-cornered races

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I was recently alerted to a new source of data on the AEC website. The AEC has always published the distribution of preferences at the seat level, as well as a more detailed dataset showing the flow of preferences from each candidate’s primary votes to the two-candidate-preferred count. They have now published this data at the booth level. This means you can see how many votes in each booth flowed to other candidates as the count progressed. Until now, the only booth-level data we had was the primary votes and the top two count.

You could probably use this data to make some interesting maps (how the flow of Greens or One Nation preferences shifts across a diverse electorate) but that’s for another day. I’m finding it most useful now because it allows us to recalculate a three-party-preferred count for electorates that have been redistributed, and there were two in particular I wanted to look at.

The Greens were not far off getting into the top two in Melbourne Ports in 2016. While the Greens candidate trailed Labor MP Michael Danby on primary votes by 3.21%, this gap shrunk to 1.12% after preferences from minor candidates were distributed. We already knew that this primary vote gap had narrowed in the renamed seat of Macnamara following the redistribution, but until now I haven’t done a 3PP count.

The new seat of Canberra has a big question mark floating over it. The best Greens areas in the ACT were previously split between Canberra and Fenner, but the new inner-city seat (confusingly taking the name of Canberra, while the old Canberra was renamed Bean) now concentrates these areas in one seat. My primary vote calculations put the Greens 14.1% behind the Liberal Party, but with over 4% of the vote going to the Bullet Train party. I was curious to know whether that gap would narrow once those Bullet Train preferences were distributed.

The answer is below the fold:

Firstly, here are the numbers. I haven’t bothered to calculate the figures for all of Victoria, since I had to download the data one seat at a time, but it was just as easy to calculate for all three ACT seats, so that’s what I did. I’ve shown the relevant stats for the pre-redistribution and post-redistribution seats:

SeatALP 3PPLIB 3PPGRN 3PPALP 2PPGRN gap
Melb Ports pre28.7043.7227.5851.381.12
Macnamara post28.2543.8227.9351.230.32
Fenner pre48.4133.6817.9263.8915.76
Canberra pre44.2839.1916.5358.4622.66
Bean post45.9338.8515.2258.8623.63
Canberra post44.3734.6420.9962.9513.65
Fenner post48.6935.6915.6261.8220.07

My estimate is that the gap between Labor and the Greens in Macnamara narrows from 1.1% to 0.3%. It’s worth noting that redistribution estimates are not perfect. In particular the methodology for distributing special votes could do with some work – I just distribute them in proportion to voter movements, not taking into account that the voters in the area which moved may not be representative of their whole old electorate. So a margin of 0.3% is the statistical equivalent of a tie.

The news is less good in Canberra. The 3PP gap between Liberal and Greens is only slightly narrower than the primary vote gap, suggesting the Greens didn’t benefit much from Bullet Train preferences. Of course, the Greens are a long way away from winning in Canberra, but they will presumably be putting up a much more serious fight in the seat than they have in past lower house races in the ACT, and may also benefit from the absence of a sitting Labor MP. I wouldn’t be surprised to see that 13.7% gap narrowed significantly, but it will be hard to close it completely and make the top two.

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9 COMMENTS

  1. Interesting to see how close the Greens are in Macnamara. Assuming good preference flows from Labor, that would certainly put the Greens in contention for another seat.

    In relation to Canberra, isn’t this discussion rather academic, since the difference is that Labor still leads at the 3PP stage, so even if they could get their vote up to overake the Liberals in to second place, the Libs will still preference Labor over them and keep Labor in the seat.

    Of course this is all predicated on the Libs not changing their policy on preferencing Labor over the Greens, but there’s no benefit to them to overturn that policy.

  2. Of course, I don’t think the Greens will win Canberra in 2019, but if they can come into the top two it pushes the seat far up the list in terms of targets and makes future campaigns more credible.

  3. Can you do the same analysis with Lab/Lib/NXT in SA seats? I’m particularly interested in Boothby and Sturt.

  4. Yes, will add to the list! But I just squeezed this in a quick break. Finished my guides to ACT/SA seats last night, and I will have a podcast to edit and then the VIC data will be ready to make those guides, so won’t have any more spare time until August.

  5. So in Canberra, if the Greens were getting a 3PP swing directly from Labor, the swing they would need to overtake Labor is actually less than the gap between them and the Liberals.

  6. The 3CP count in Melbourne may also be worth a look because it is a close contest (the 2CP being counted changed when the AEC worked out that the Liberals had overtaken the ALP on preferences) that determines who comes third and thus what is currently the margin of Bandt`s victory (potentially safe versus marginal).

    Kooyong and Gellibrand were also relatively close between first and second on 3CP at the last election, although their safety for first place makes the results rather academic.

  7. @morgieb The retirement of Danby could swing either way. His Zionist sympathies may have allowed him to attract some voters that will move to the Liberals if a more conventional Labor candidate is chosen. However it’s also very likely that the same positions may have contributed to the growth of the Greens vote.

    So there is a balancing act for Labor in their choice of candidate. A left-leaning candidate may allow them to improve their margin over the Greens. But if that comes at the expense of losing voters to the Liberals, their 2PP margin is vulnerable.

    Normally I’d dismiss the idea that the individual politics of a major-party candidate (cf. their personality) would have much of an impact on 2PP. But the narrative around Danby has always embraced that idea. We might be about to find out if it is real.

  8. In order for a 3rd party to win a seat, the following things need to happen.
    1) The third party needs to overtake one of the two majors
    2) The other major can’t get a majority
    3) The first majors preferences favour the 3rd party over the other major.

    With that the seats to look for are the seats where Liberals are winning the primary vote, and Greens are close to overtaking Labor. Greens actually need to get quite a few votes over Labor in Green vs Labor seats like Batman and Wills when Liberals are running.

    I also think this gives Centre Alliance a chance to win in Barker but not Grey. I’m anticipating both Liberal and Centre Alliance will lose votes to Labor; in Grey Labor will jump into 2nd, but the gap is too big in Barker.

    One Nation could win a seat where Labor wins the primary vote and One Nation overtakes the Liberals and wins with their preferences. Not sure where that will happen though as most of the areas where that happened in the state election have LNP incumbents. Plus, there’s every chance Liberals will put One Nation last to avoid the negative effect PHON preferences had in Brisbane seats.

    Independents might be a factor in safe Liberal and National seats, but I can’t see any emerging in 3 corner contests.

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