Poll of polls: National-Act Government now most likely, data shows

Prime Minister Chris Hipkins and National leader Christopher Luxon. Luxon appears more likely to become the next PM as shown in the Poll of Polls.

A National-Act tie-up is the most likely Government according to the Herald’s poll of polls, which has been updated with the results of the latest Talbot Mills poll.

There is now almost no chance of Labour and the Greens getting over the line by polling day, according to the data.

If they are to govern, they will need the help of Te Pāti Māori - and the numbers show even that does not give the three-party left bloc better odds than a National-Act Government.

The tool runs a simulation based on polling data from multiple public polls and previous election results to get a feel for what might happen on election night. Running that simulation multiple times gives people a sense of how likely various outcomes might be.

The Herald ran 8000 simulations of possible outcomes if the election were held this Saturday. Simulations were also run on the likely outcome of an election on the actual polling day, October 14. The simulation includes the results of the most recent poll, the Talbot Mills internal poll, leaked to the Herald on Tuesday.

Results are expressed in terms of probabilities, which is the number of times a particular result occurred.

If an election were held this weekend, the simulation found Labour and the Greens in a position to form a government 0.0 per cent of the time. With the help of Te Pāti Māori, they were able to get over the 61 seat line in 23 per cent of simulations.

National and Act’s chances are better. They have a 57 per cent probability of forming a government if the election were held this weekend.

In the unlikely event National, Act and Te Pāti Māori learn to become friends again, as they did between 2008 and 2019, their odds of forming a government rise to 99.9 per cent if the election were held this weekend.

A hung Parliament occurred 20 per cent of the time.

Looking into the future, Labour and the Greens’ probability of governing alone rises just slightly from 0.0 per cent to 1.9 per cent. The probability of a Te Pāti Māori tie-up becomes 34.1 per cent.

A National-Act coalition remains the most likely outcome on polling day with a probability of 53.2 per cent, and a hypothetical tie-up including Te Pāti Māori occurred 95.7 per cent of the time.

Party vote

The average party vote in the Herald’s simulations was 33.3 per cent for Labour and 35.5 per cent for National.

Act was on 11.2 per cent, the Greens 8.3 per cent, and Te Pāti Māori 3.9 per cent.

TOP was on 2.6 per cent, and NZ First was on 3.1 per cent.

How the ‘poll of polls’ works

As part of its 2023 election coverage, the Herald is launching its “poll of polls”. Our “poll of polls” combines polling from different pollsters to predict party vote for the 2023 election.

The model imagines that in any given week there exists an unobserved voting intention that is partially measured via opinion polls and is accurately measured once every three years by an election.

The model can also make predictions about how voting intention can evolve between now and election day.

This approach enables us to estimate each polling organisation’s accuracy in previous elections and then use that to inform our predictions.

The Herald has based its model on a New Zealand election forecast developed by statistician and data scientist Peter Ellis. Ellis developed the model in a private capacity prior to taking on his current role as director of Statistics for Development Division at the Pacific Community (SPC).

Ellis also used the model to forecast the Australian election. Similar models have been used to make predictions about the German and Swedish elections. Both Germany and Sweden have proportional representation electoral systems similar to New Zealand’s MMP system.

Our “poll of polls” combines results from a range of pollsters, who are signatories to the NZ Political Polling Code, specifically Curia, Kantar Public, Talbot Mills, and Reid Research.

Details of the model, including the source code, are available here. Between now and the election we will be looking to improve some aspects of the model, in particular the handling of polls which do not provide polling data for some of the smaller parties.

Currently, in order to be included in the model, a party must have polled over 2.5 per cent in at least three polls.

It is assumed that parties currently holding an electorate seat retain them and no other parties win an electorate seat. Future versions will enable readers to modify this assumption.