It is always a challenge to understand how a given share of the vote for a political party translates into a certain number of seats under the single-member electorate system used in most Australian jurisdictions.
We have a number of tools to help with this task, such as the pendulum and historical swing trends, but most of these tools don’t work that well in a multi-party environment, such as the one we’re now seeing with One Nation’s surge in support.
For this blog post, I’m going to use some limited data we’ve gained on how One Nation is polling in the state seats of Victoria to model how votes might turn into seats if One Nation’s vote is higher or lower.
To do some more sophisticated modelling of how votes might turn into seats, we would ideally get an estimate of how much of the vote each party has in each seat. It doesn’t need to be perfect, but it would give a rough shape of how votes are distributed. At a national level, two MRP polls have been published this year: one by DemosAU and one by Redbridge/Accent.
At a state level, none have been published in Victoria (or any other state). But we do have one MRP that was leaked to the media.
Redbridge/Accent conducted an MRP for Victorian Trades Hall in June 2026 which was eventually leaked to media outlets including the Australian Financial Review.
This MRP reported a primary vote of 27% for One Nation, with Labor and the Coalition tied on 26%, and the Greens on 13%. It’s basically a three-way tie between the three leading parties.
This MRP reports seat totals based on these votes of 39 Coalition seats, 35 Labor seats, 12 One Nation seats and 2 Greens seats. But there’s been a lot of disagreement about those seat totals.
The MRP asked voters to fill out a full ballot, and thus used preferences as allocated by the voter. It is more traditional in polling, particularly for MRPs, to use historic preference flows instead.
While we have less data on how preferences flow with a strong One Nation vote, there are definitely some strange figures in the Redbridge/Accent MRP preference flows. In particular, the MRP suggests that Coalition voters are favouring Labor over One Nation, while recent elections have suggested the opposite.
It may be that part of the discrepancy comes from Liberal how-to-vote cards. While those may influence voters in a real election, the MRP respondents haven’t had that advice.
It makes a big difference in a scenario where One Nation makes it to the top two in numerous seats. I have produced my own preference flow estimates based on previous elections. With the same primary votes as the Redbridge/Accent MRP, the seat totals end up very different:
| Party | Redbridge/Accent | Tally Room |
| Coalition | 39 | 31 |
| Labor | 35 | 30 |
| One Nation | 12 | 27 |
| Greens | 2 | 0 |
The specific preference flows make a huge difference. I originally had Coalition to One Nation preferences a bit higher but tweaked it after feedback from Kevin Bonham, and that dropped the One Nation seat count from 31 to 27. There is also a lot we don’t know about how Coalition and One Nation preferences will flow in Labor-Greens contests and this makes a big difference as to the Greens seat count.
Anyway, while I have questions about the MRP’s preference flows, I do appreciate the provision of primary vote figures for every seat in the state, which then allows us to do some other analysis.
So I have taken those primary vote figures for the 88 seats, and I have then applied a model where I increase the One Nation primary vote of 27% by increments of 1% until they get to a primary vote of 37%, and also decrease their vote to 17%. For each increment of 1%, I transfer one third of a percentage point from Labor, and two thirds of a percentage point from the Coalition.
I also considered a model where there was a 1:1 swap between One Nation and Coalition votes, to model the impact of changes within the right-wing part of the electorate. I suspect the Coalition contributed more of One Nation’s vote as their vote started to climb, but this model only tries to model a One Nation vote starting at 17%, at which point that early climb has finished.
So, what did I find? This next chart shows how many seats each party would win for a given One Nation vote between 17% and 37%, using my preference flow estimates and using Redbridge/Accent’s primary vote estimates as a starting point with One Nation on 27%.
I have assumed that the top two candidates make the 2CP. If two candidates are tied for second place, I have run two different counts for each of the possible 2CPs, with each result worth half a seat. This explains why some results involve a party winning half a seat.
The number of One Nation seats is very low until they get to about 22%, and then the seat count climbs relatively consistently until they get to the low 30s, then it slows down again. In this model, Labor and Coalition seat wins are roughly neck-and-neck as the One Nation vote climbs.
Interestingly, a primary vote of 32% is enough for a very slim One Nation majority. In that scenario, the Coalition is on 24.3% and Labor is on 22.7%. With quite a clear right-wing majority, it’s not surprising that the dominant conservative party would be able to win a majority in a divided contest.
This is just one model, but I think it does give some insights into how One Nation might perform in seats for a given vote.
Another feature of this modelling that I found interesting was how each party’s vote share translates differently into seat shares. Each party has a different preference position – Labor benefits from the Greens in most seats. The Coalition does a bit better than One Nation if they face off. At the recent state election in South Australia, One Nation narrowly outpolled the Liberal Party, but won one less seat. I think it’s reasonable to expect a similar primary vote for the two parties would see the Coalition win more seats.
So I went into my election model and compared how many seats each party wins on the same primary vote. The range of results is wider for One Nation than the other parties, since the model assumes a greater range of change for One Nation.
For most of the comparable range, the major parties win more seats than One Nation on the same vote.
On the current polling, with all three parties in the mid-20s, the three parties would win relatively similar numbers of seats. If any of the three parties was to boost their support into the 30s, they would then have a chance at winning a majority, because there is quite a steep dropoff in support.
So who is the State Leader of One Nation in Victoria?
As it gets closer to November and actual voters have to focus on a choice, surely One Nation vote fades in the closing weeks.
Is Tassie a better model than SA? Ie people vote on who they think the likely winner is and vote accordingly.
There is a lot of anger towards the state Labor government and state Liberals for various reasons, voters might feel that a state election is not as consequential as a federal election and feel free to give the major parties a kick. Given how similar the primary vote is between all 3 of the parties it is way too difficult to decipher who win certain seats.
It is somewhat funny that in the midst of all this we’ve forgotten that there is an elected ON member already in the upper house and we haven’t heard a peep out of her in the media.
I think that some One Nation-leaning voters may hold their noses and tactically vote for the Coalition. It is because they see voting for the Liberals or Nationals as the traditional way to defeat Labor. Both parties would also make that claim as the sole way to change the government.
I expect the ‘other’ vote (not ALP, LNP, GRN, ONP) to become more left-wing and favour Labor on preferences (against LNP or ONP). I think ONP will monopolise the right-wing, minor vote and take votes off parties like Freedom, FF or DLP. Also, a lot of protest voters and anti-establishment voters in working-class or culturally diverse seats in Greater Melbourne will shift to Vic Socialists.
This is such a good illustration of the difficult position the Greens are in, in a few parliaments. They can reliably consolidate their vote enough to win or come close in a distinct band of seats, and have done so for many elections now especially in Victoria. But the composition of the other votes in the seat matters hugely to who they face in the 2CP, and which votes are out there to get them across the line or not.
The Greens are polling well in Victoria, there’s energy further left that is fairly disciplined in preferencing them, plenty of Labor voters want a new home, but it’s still totally plausible for the Greens to get anywhere between 0 and 7, or even more if the Libs put Labor last.
ONP campaigned hard on fighting the ‘uniparty’ in SA – I think their message this time is a little more delicate as their voters will prefer a change of government and on this occasion they’ve already announced they’ll preference the Coalition whilst back in SA they ran open tickets whilst the Liberals preferenced them without reciprocation!
In SA people were choosing the opposition, in VIC there is a serious choice about the government, ONP are likely to be scrutinised a fair bit more in the lead-up
Is there a Ben Carroll bounce coming?
@Lars Von Trier
I believe Redbridge is releasing a poll this week although it was taken before the leadership change but it will be sometime before the full effects of Ben Carroll leadership can be seen if it was mistake or a excellent decision. It is worth mentioning the last poll before Allan resigned had the Liberals leading 52/48 which is surprisingly competitive for such an old government and deeply unpopular premier.
The Labor primary vote shown in polling is close to what Labor got when they were wiped out at the 2011 NSW and 2012 QLD state elections (which was 26% to 27%). The only difference is that the LNP were mega popular at those two elections, getting half the primary vote and One Nation’s support was negligible. Since then, there has been a breakdown in the two party system. Also, Jess Wilson isn’t as popular as her interstate counterparts were in 2011 and 2012.
The Jacinta Allan brand was toxic in that she had a net favourability of -50. The Labor 2PP, on the face of it, didn’t look too bad given her unpopularity and the aging government.
If it’s a battle of coming first or second on preferences in Victoria – doesn’t it make sense to maximise your first preference vote over seeking preferences, as at least some of those preferences don’t come back?
Secondly – if there is a contest for the “middle ground” between Labor and Liberal the higher your first preference vote in polls the more likely people are to vote for you over the other Party to stop One Nation?
So basically Ben Carroll has to win back the base or most likely about 5% (which is notionally with One Nation) to win. Not impossible.
James Campbell from the Herald Sun (who otherwise made some ok comments. i.e. on EV subsidies) has declared on Insiders that the theories above that Ben has posited are WRONG.
Let’s see, but it must be wonderful to go through life so certain about future events that are so demonstrably uncertain…..
I don’t think James understood the point that Tom was making…
I thought Tom was just repeating the results of your alternative scenario testing, as shown in your table above.
Campbell also made a big point about ON preferences flowing to Liberal with near the same discipline as GRN to ALP, which has not yet been seen in the wild (in an election). If its even somewhat true, then following the logic means Liberal preferences would be flowing better to ALP vs ON than most people think, when the Labor primary has dopped from the last election.
Anyway its all supposition and just because a certain flow rates occurs in one jurisdiction at a given point in time, doesn’t make it a hard and fast rule