New Zealand, Old Mistakes

NZ was the first in our rapid-fire electoral predictions, with Queensland going to the polls next weekend and the US Presidential in the following week. My apologies, also, to the ACT who I mistakenly thought was in November but occured simultaneously with New Zealand; still, they've got Hare-Clarke STV across multi-member electorates so the territory's got their ACT together.

The Electorates

The hasty formulation of my NZ predictions also introduced an unforced error: my list of electorates was out of date, building on last election's results without taking redistribution into account. Several seats I predicted did not exist this year, and several new seats were created. Fortunately, several of these new seats were broadly comparable to previous, abolished seats: Give or take some small areas Dunedin North was replaced by Dunedin, Helensville was replaced by Kaipara ki Mahurangi, Manukau East became Panmure-Ōtāhuhu, Clutha-Southland dropped the Clutha- to become Southland, Dunedin South is now Taieri and Rodney became Whangaparāoa.

These are marked below with an asterisk, but I have carried over my predictions.

ELECTORATE	INCUMBENT	PREDICTION	RESULT
Auckland Central	National	Labour	Green
Banks Peninsula	New Seat	None	Labour
Bay of Plenty	National	National	National
Botany	National	National	National
Christchurch Central	Labour	Labour	Labour
Christchurch East	Labour	Labour	Labour
Coromandel	National	National	National
Dunedin	New Seat	Labour*	Labour
East Coast	National	Labour	Labour
East Coast Bays	National	National	National
Epsom	ACT	ACT	ACT
Hamilton East	National	Labour	Labour
Hamilton West	National	Labour	Labour
Hauraki-Waikato	Labour	Labour	Labour
Hutt South	National	Labour	Labour
Ikaroa-Rāwhiti	Labour	Labour	Labour
Ilam	National	National	Labour
Invercargill	National	Labour	National
Kaikōura	National	National	National
Kaipara ki Mahurangi	New Seat	National*	National
Kelston	Labour	Labour	Labour
Mana	Labour	Labour	Labour
Māngere	Labour	Labour	Labour
Manurewa	Labour	Labour	Labour
Maungakiekie	National	Labour	National
Mt Albert	Labour	Labour	Labour
Mt Roskill	Labour	Labour	Labour
Napier	Labour	Labour	Labour
Nelson	National	Labour	Labour
New Lynn	Labour	Labour	Labour
New Plymouth	National	Labour	Labour
North Shore	National	National	National
Northcote	National	Labour	Labour
Northland	National	National	National
Ōhariu	Labour	Labour	Labour
Ōtaki	National	Labour	Labour
Pakuranga	National	National	National
Palmerston North	Labour	Labour	Labour
Panmure-Ōtāhuhu	New Seat	Labour*	Labour
Papakura	National	Labour	National
Port Waikato	New Seat	None	National
Rangitata	National	Labour	Labour
Rangitīkei	National	National	National
Remutaka	Labour	Labour	Labour
Rongotai	Labour	Labour	Labour
Rotorua	National	Labour	National
Selwyn	National	National	National
Southland	New Seat	National*	National
Taieri	New Seat	Labour*	Labour
Takanini	New Seat	None	Labour
Tāmaki	National	National	National
Tāmaki Makaurau	Labour	Labour	Labour
Taranaki-King Country	National	National	National
Taupō	National	National	National
Tauranga	National	National	National
Te Atatū	Labour	Labour	Labour
Te Tai Hauāuru	Labour	Labour	Labour
Te Tai Tokerau	Labour	Labour	Labour
Te Tai Tonga	Labour	Labour	Labour
Tukituki	National	Labour	Labour
Upper Harbour	National	National	Labour
Waiariki	Labour	Labour	Maori
Waikato	National	National	National
Waimakariri	National	National	National
Wairarapa	National	Labour	Labour
Waitaki	National	National	National
Wellington Central	Labour	Labour	Labour
West Coast-Tasman	Labour	Labour	Labour
Whanganui	National	Labour	Labour
Whangaparāoa	New Seat	National*	National
Whangarei	National	National	National
Wigram	Labour	Labour	Labour

Banks Peninsula, Port Waikato and Takanini are made up of the remnants of several former electorates and no prediction can be honestly recorded against these. Excluding these three seats there are 69 seats of which 61 we predicted rightly: 88.4%. Including these three as failed predictions, success falls to 84.7%.

Normally these wouldn't be great results, but first-past-the-post is somewhat more volatile and unpredictable if the system can sustain more than two credible parties (see: New Zealand, United Kingdom; compare: United States of America).

Banks Peninsula, Port Waikato and Takanini (as noted) were incorrect predictions purely (and technically) by virtue of not being considered. The other eight incorrect predictions are Auckland Central and Waiariki where smaller parties unexpectedly triumphed (Greens and Maori respectively); Ilam and Upper Harbour where Labour won safe National seats; and Invercargill, Maungakiekie, Papakura and Rotorua where Labour failed to unseat vultnerable Nationals despite a strong swing to them.

Auckland Central and Waiariki both had targetted polling that was upset by the results last weekend. That being said, targeted polling like this is normally a good sign the race is worth watching.

Ilam is an unexpected win for Labour. Since it was created in 96 it has been won by the Nationals; in 2014 Nationals had over 50% of the total votes and more than a 10,000 vote lead over Labour; in 2017 Labour didn't even come second. Upper Harbour likewise has always been a National seat, though admittedly much younger, and in 2017 nationals had an almost 2:1 lead over Labour and over 50% of the votes. To see these seats fall must have been a shock for the Nationals and the cherry-on-top for Labour in a genuinely historic win.

Invercargill and Papakura were bold predictions in hindsight. Papakura has been National since creation in 2008, as was its precedessor 1978-2003. Invercargill, although it has a long and mixed history, has been National for a decade and a half. Nationals won with over 50% of the vote in 2017 in both seats. Labour was definitely closer here last election than in Ilam or Upper Harbour, but these seats are sticky. Looking at these facts would give reason to pause on the more general, nation-wide predictive methods but the simple fact is that such individual races are too time consuming to study at this level in each seat. Invercargill was called hastily. Papakura was simply a mistake.

Maungakiekie and Rotorua, on the other hand, should probably have flipped. They have a strong National vote in recent history, but they were close in 2017 and the swing should have brought them back to Labour. These seats are two of those abberations determined by the campaign on the ground despite national trends.

The List

The prediction for the final composition of the NZ parliament was:

Labour -- 61 seats

National -- 41 seats

ACT -- 10 Seats

Greens -- 8 seats

 

This was alsmost blown apart by Waiariki, where the election of a Maori party candidate made the party eligable for several seats. As it happened the national vote was so low that no additional Maori seats were won.

The actual result was therefore:

 

Labour -- 64 seats

National -- 35 seats

ACT -- 10 Seats

Greens -- 10 seats

Maori -- 1 Seat

Compared to the prediction this saw worse peformance from National (▼6) and improved results for Labour (▲3), Greens (▲2) and Maori (▲1) parties. ACT performed as expected.

Quantifying this success is dificult; it would be oversimplistic to say that 6 seats predicted for Nationals were won by other parties, and therefore 114 seats (95%). The Mixed-Member Proportional representation used in NZ doesn't really work that way; even small changes in the voting number can cascade through the quota calculations and change the order that seats are won, technically making a number of unpredicted appointments that will tend to balance out over the count.

Instead, it is best to measure this result qualitatively; the prediction was that Labour would, for the first time for any party under this system in NZ, win a majority government. This turned out to be correct.

 

Another useful metric, if numebrs are your thing as much as they are mine, is to look at the difference between seats predicted and won for each party as a percentage of the prediction; since the final composition is based on national proportions this allows a rough measure of predicted % support against actual % support.

For example, Labour won 64 seats but was predicted to win only 61. This is a difference of ▲3 and 3/61 x 100% = 4.9%, or a 4.9% error, or a (100% - 4.9% =) 95.1% accuracy

Results

Electoral predictions:

61 correct/69 predictions = 88.4%

61 correct/72 possible seats = 84.7% (Three seats mistakenly not predicted)

List predictions:

Labour to form NZ's first majority government under MMP: correct

Labour ▲3 on a predicted 61 seats: 95.1% accuracy

National ▼6 on a predicted 41 seats: 85.4% accuracy

ACT correct prediction of 10 seats: 100% accuracy

Greens ▲2 on a predicted 8: 75.0% accuracy

Maori 1 Seat won when none predicted: 0% accuracy