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.
