The use of mixed-member proportional representation allows ready conversion of a party's support into a party vote percentage and therefore a number of seats in Parliament. Projections generally assume no changes to electorate seats each party holds (ACT retains Epsom, Māori retains Waiariki, Labour retains Te Tai Tokerau, etc.) unless there is a specific reason to assume change. For example, after Peter Dunne announced his retirement, projections stopped assuming United Future would retain Ōhāriu. Other parties that do not pass the 5% threshold are assumed to not to win an electorate and therefore gain no seats.
Radio New Zealand takes a "poll of polls" average to produce their forecast. The New Zealand Herald bases theirs on a predictive model incorporating poll data as well as past election results and past poll accuracy.[1] Newshub and 1 News and produce projections based on their own polls only.
When determining the scenarios for the overall result, the minimum parties necessary to form majority governments are listed (provided parties have indicated openness to working together). Actual governments formed may include other parties beyond the minimum required for a majority. This happened after the 2014 election, when National only needed one seat from another party to reach a 61-seat majority, but they formed a 64-seat government with Māori, ACT and United Future.
| Party | Newshub[2] 13–20 Sep 2017 poll [final] |
1 News[3] 15–19 Sep 2017 poll [final] |
Roy Morgan[4] 28 Aug–10 Sep 2017 poll [final] |
Radio NZ[5] as of 21 Sep 2017 [final] |
NZ Herald[6] as of 22 Sep 2017 [final] |
Stuff[7] as of 22 Sep 2017 [final] |
Official result | |
|---|---|---|---|---|---|---|---|---|
| National | 56 | 58 | 50 | 55 | 56 (±2) | 54 | 56 | |
| Labour | 45 | 46 | 49 | 46 | 47 (±3) | 46 | 46 | |
| NZ First | 9 | 6 | 7 | 8 | 9 (±2) | 7 | 9 | |
| Green | 9 | 9 | 11 | 9 | 7 (±2) | 10 | 8 | |
| ACT | 1 | 1* | 1 | 1 | 1 | 1 | 1 | |
| Māori Party | 2** | 1 | 2 | 1 | 1 | 1 | 0 | |
| Seats in Parliament | 122 | 121 | 120 | 120 | 120[nb 1] | 120[nb 2] | 120 | |
| Overall result (majority) | National−NZ First (65) | National−NZ First (64) | Labour−Green−Māori (62) | National–NZ First (63) | National–NZ First (65) | National–NZ First (61) | National–NZ First (65) | |
| Labour−Green−NZ First (63) | Labour−Green−NZ First (61) | Labour−Green−NZ First (63) | Labour−Green–NZ First (62) | Labour−Green–NZ First (63) | Labour−Green–NZ First (63) | |||
- * indicates an overhang seat
- ^ The Herald's forecasted numbers are the medians of all likely outcomes for that party. The sum of the parties' forecasted seats does not necessarily equal the total likely seats in Parliament. In this table, "Seats in Parliament" is calculated by adding the number of forecast overhang seats to 120, even if the individual parties' seat projections do not add up to this number.
- ^ Stuff's projected numbers add up to 119, but this outcome is impossible. Calculation (based on exact percentage) shows that 120th and last seat would be allocated to Labour. Taking into account that the polling average have three significant figures it is not possible to decide which party get the last seat.
References
- ^ "Herald election forecasts explained". NZ Herald.
- ^ "Newshub election poll: Either National, Labour could take power". Newshub.co.nz. 21 September 2017.
- ^ "New poll: National takes huge lead in bombshell 1 NEWS Colmar Brunton poll". Television New Zealand. 20 September 2017.
- ^ "New Zealand Election on a knife edge but Labour favoured with the support of the Greens & Maori Party as 'Jacindamania' pulls support from National & New Zealand First". Roy Morgan.
- ^ "Poll of the final polls - too complicated to call". Radio New Zealand.
- ^ "Election forecast". New Zealand Herald.
- ^ "Stuff poll of polls: Election result too close to call". Stuff.