Running that simulation multiple times provides a sense of how likely various outcomes might be. The results are expressed as probabilities. The latest simulation takes data from the most recent flurry of polls.
As NZ First gets closer to polling above 5 per cent and entering Parliament, the Herald has looked at the likelihood of the party entering Parliament and forming a government.
NZ First has said it will not work with Labour, so we have included them with the right bloc. Act says it would not sit around the Cabinet table with NZ First but has not said that it would withhold supporting such a government on motions of confidence, leaving some wriggle room for a National-NZ First-Act formulation.
If the election were held this weekend, there is an 80.5 per cent probability of a National-Act-NZ First government.
If we extend out to election day, Labour, the Greens, and Te Pāti Māori have a 21.1 per cent chance of getting over the line.
This compares to National and Act, who have a 67.2 per cent chance or a 76.7 per cent chance if you add in NZ First.
The Poll of Polls also simulates the likely party vote of the different parties. National is in the lead on 34.5 per cent, Labour following behind on 30.8 per cent.
Act is next on 11.9 per cent, followed by the Greens on 10.2 per cent.
NZ First is still below 5, polling 4.5 per cent, although they could poll as high as 5.5 per cent.
Te Pāti Māori is on 3.1 per cent and TOP on 2.4 per cent.
How the Poll of Polls works
As part of its 2023 election coverage, the Herald has launched a Poll of Polls, which combines polling from different pollsters to predict the 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 intentions 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 New Zealand 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.
