Margins in strong Greens seats


There are a handful of seats in the House of Representatives where the Greens are within spitting distance of winning the seat. In nearly all of them, however, the true margin is hidden by the AEC’s methods of measuring marginality. Margins are calculated by referring to the two-candidate-preferred vote, but this doesn’t take into account the possibility that a candidate in third place may overtake the second-place candidate and be in a winnable position.

Greens marginal seats run into what psephologists call “non-monotonicity”, whereby one group’s preferences are not reciprocated. In monotonic system, a candidate cannot be harmed by receiving an extra vote. In recent federal elections, Liberal preferences in strong Greens seats have been directed to the Greens over Labor, putting the seat in a position where a Green in third place might win against Labor in a 2CP count, on Liberal preferences, but the preferences are not reciprocated, with Greens voters preferencing Labor over Liberal. Thus a seat may be registered as a 19.5% margin for Labor, as in the case of Sydney, even though the Labor vs Greens margin would be much smaller. Even if the result isn’t reversed by a change in the order of elmination, it’s possible that a seat can shift from “Very Safe” to “Marginal”.

At the 2007 election, only one Greens candidate managed to come second after preferences, in the seat of Melbourne, where the Greens overtook the Liberals on preferences from minor candidates and registered over 45% of the two-party-preferred vote, making the seat marginal. But there are a number of seats that fit the criteria of Greens marginals but don’t appear as such on the pendulum. These criteria are:

  • A reasonably high Greens vote (above 15%).
  • A large gap between the two major parties, with the weaker of the two (usually the Liberal) very low (usually below 30%).

The Greens managed to attract 82.5% of Liberal preferences in Melbourne at the 2007 election. In order to determine the next five most marginal Greens seats, I translated this proportion of Liberal votes to the Greens, to determine a two-party-preferred vote between Labor and Greens. I excluded all seats where the margin between Liberal and Greens is greater than the Labor-Greens margin. For example, in the case of Grayndler, I calculated a 60-40 margin, and the Liberals beat the Greens by 2%. I assume that if the Greens were to gain 10% of the 2PP vote they would manage to overtake the Liberals.

Anyway, here is my calculations.

  1. Melbourne – 54.7-45.3
  2. Sydney – 55-45
  3. Grayndler – 60-40
  4. Cunningham – 61-39
  5. Denison – 61-39
  6. Batman – 62-38

Comments, anyone?

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  1. I’d be interested to see what the results are in the state seats in inner city areas. Of course, this would be made all that much easier if the AEC/ECQ/VEC/etc. provided a database of ballot papers broken down by electorate/booth. Perhaps the only benefit of electronic voting is the potential for open-ness about the ballots actually cast?

  2. I don’t know about other states, but in NSW and Victoria it’s made a bit easier because we have actually overtaken the Liberals in Balmain, Marrickville, Melbourne, Richmond, Northcote and Brunswick. In Fremantle, we are behind the Liberals, but on election night Antony Green’s computer projected a Greens victory whenever we overtook the Liberals, for what that’s worth.

  3. More information:

    2.01 – Melbourne
    3.63 – Brunswick
    3.64 – Richmond
    3.75 – Balmain
    7.48 – Marrickville
    8.52 – Northcote

    It’s worth noting that in the Victorian seats, with compulsory preferential voting, the Liberals preferenced the Greens, whereas in NSW the Liberals exhausted.

  4. I think Batman’s a fair way off. There are still too many traditional working-class Labor supporters there for the Greens to make a serious run, despite strong Green support in places like Northcote. Depending on the NSW redistribution, Cunningham and Grayndler might be the same.

    Obviously their best chance are seats where Green support is high throughout, not just some strong pockets. Melbourne, Sydney and probably Denison would be most likely to fit that criteria.

  5. All of them except Sydney and Balmain Melbourne are still well-off, but I think the margins reflect that. I don’t think it’s unreasonable to think a 12% swing would knock over Martin Ferguson, I don’t think that will happen in the next election. But I could see that happening towards the end of this government (ie. after 3 or 4 terms when it gets tired).

  6. Cunningham a couple of elections ago showe what happens when the ALP vote splintered and it was captured at a bye-election by the Greens.

    the ACT is interesting but shows the difficulties faced by the Greens in single member electorates.-Two strong ALP seats – but based on an electorate with a high education lelvel that is gradually worming to the idea of voting Green and where the Liberal Party looks largely irrelevant.

    Base level on Reps figures is creeping up 13% and in the Senate reaching levels tantalisingly just short of knocking off the Liberal Senator with ALP above quota preferences.

  7. In terms of Greens votes, both ACT seats come out about the same. In Fraser I calculated the Labor-Greens margin as 58-42, with the margin in Canberra at 57.5-42.5. Of course, the margin between Liberal and Greens for second place is 18-23%, meaning that an 8% swing vs. Labor wouldn’t win the seat for them.

    On the other hand, if the ACT managed to gain a third seat back, the central seat could be very competitive for the Greens.

  8. I think the ACT is a particularly interesting case in regards to the chances of the Greens winning House of Representative seats, especially when the ACT gains a third seat back.

    Currently the ACT has the two largest House of Representative seats in the country (unless that has changed recently), with the territory only just missing out on gaining a third seat last election. With a growing population it is only a matter of time until the ACT gains a third seat.

    It is likely that the three seats would split similarly to how the ACT legislative assembly seats are split, with some important changes. It would be like that the seats would be made up as such: (1) – Gungahlin and Belconnen (2) Inner North, Inner South and Woden and (3)Weston Creek and Tuggeranong. If this were to occur the middle seat would become immediately attainable for the Greens. These areas are very strong for the Greens and I am pretty certain that if you were to put them together the Greens would outpoll the Liberal Party in those seats (I will try and do some numbers soon – I am working on ACT polling maps at the moment). The question would be whether these two parties would outpoll Labor, which I think is definitely possibly, especially given recent polling.

  9. The middle seat would probably contain the affluent inner southern suburns of Canberra (Red Hill, Deakin, Forrest) plus Campbell on the north bank. Possibly the Liberal vote would still be too high for the Greens to finish second, unless Liberals are encouraged to vote tactically. This arrangement would also make it less difficult for the Liberals to win the other two seats, although they’d still be Labor leaning.

    Perhaps this is why Labor is not making as big a fuss as some might think about Canberra only having two seats…..

  10. If you look at the polling numbers I think there would be very little chance of the Liberals picking up the other two seats. Gungahlin and Tuggeranong are still both strong Labor areas.

    As for Red Hill, Deakin, Forrest and Campbell, I would argue that although they are stronger for the Liberals, there are also quite strong for the Greens. In both the 2007 Federal Election and the 2008 ACT Election the Greens polled there much better than they did in the the outer suburbs and were close to the Liberal Party. Add that to the Inner North Suburbs where in most cases the Greens outpolled the Liberal Party and I think the Greens would have a good shot at picking up that seat.

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