Election 2023: NZ Herald’s poll of polls shows incredibly tight election, Māori Party in kingmaker position

The Herald has today launched its "poll of polls". Photo / NZME

Te Pāti Māori is in kingmaker position six months out from the election, according to a new “poll of polls” from the Herald.

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 3000 simulations of possible outcomes if the election were held this Saturday.

It found that 75.1 per cent of the time, Labour, Greens and Te Pāti Māori got over the crucial 61-seat threshold required to form a government.

National, Act, and Te Pāti Māori were also likely to cross the 61-seat threshold, getting there 74.2 per cent of the time. While this makes this outcome somewhat likely in a statistical sense, it is highly unlikely politically.

The results show that a repeat of one-party government by Labour or National is incredibly unlikely.

The simulation also shows that the odds of Labour and the Greens or National and Act governing alone are fairly slim. Labour and the Greens could form a Government 11.4 per cent of the time, and National and Act could form a Government 10.3 per cent of the time.

The tool also used polls to simulate where a party’s party vote might go between now and polling day on October 14.

To use this tool, look at each party’s polling in our poll of polls. Each dot represents a poll. The line in these charts shows our estimate of a party’s party vote share. The shaded area is the likely upper and lower values of the party vote share. The closer to the edge of the cone, the less likely those outcomes would be.

How the “poll of polls” works

Today, 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% 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.