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New Zealand election polling

Llewelyn Richards-Ward writes:

Here is a forecaster apparently using a simulated (?Bayesian) approach and smoothing over a bunch of poll results in an attempt to guess the end result. I looked but couldn’t find his methodology but he is at University of Auckland, if you want to track him down…

As a brief background, we have a very centrist government position and this has been so for many years since the neo-liberalist earthquake of the 80s hit us all. Really, the two main parties, Labour and National, are a metre away from each other compared to the gulf between similar parties overseas. We have an MMP system, with 120 seats. Usually there is a coalition government, which has given us very stable growth, positive social outcomes and reasonable taxation. This election is one where the swings in polls and voter options have been startling, for a small place like ours. First, the Green Party co-leader admitted to welfare fraud, actually told us all about it, hoping to garner sympathy for their social issues. She was a goner after public outcry. We all hate cheaters. Then the leader of a stabilising minor party decided to quit, probably as he was polling lower than usual. That party is probably now in that place called oblivion as, without an electorate seat or 5% polling, no ticket to parliament is handed out. Then the Labour party, lately rather staid and uninspiring, killed off yet another leader and a new, female, young, face appeared. This has been dubbed “jacinda-mania”. Lots of energy, she has a PR background, and appeals to the young chic voters (most of whom never actually vote). Labour, after leaping from the low teens to 43% (or something, in some polls) as a result of a fresh face (same policies and other candidates), now is slipping back again. Today, after stupidly promising a tax working group (which we all know means with people who will eat towards their preferred outcomes), they have U-U-turned and now say they will come up with ideas and put it to the electorate next election.The lesson again is don’t ask voters to write blank cheques and don’t threaten middle-NZ with property taxes whilst large corporates are paying very little. NZ, given mostly we are doing well, is not a place easily swayed into change when status-quo seems to be working. Who knows what tomorrow brings — I personally will be voting early to reduce the tension of it all.

My take is that all the pollsters are off-centre because of poll variability. It seems that the above issues have induced changes of preference in the public, rather than simply variability being about noise, so-called.

I don’t know enough about New Zealand to comment on this one. I did read an interesting book about New Zealand politics back when I visited the country in, ummm, 1992 I think it was. But I haven’t really thought about the country since, except briefly when doing our research project on representation and government spending in subnational units. New Zealand is (or was) one of the few countries in the world a unitary government in which no power was devolved to states or provinces.

Anyway, regarding Richards-Ward’s final paragraph above, I would expect that (a) much of the apparent fluctuation in the polls is really explained by fluctuations in differential nonresponse, but (b) you’ll see some instability in a multi-candidate election that you wouldn’t see in a (nearly) pure two-party system such as we have in the United States.

P.S. I feel like I should make some sort of Gandalf joke here but I’m just not really up for it.


  1. Peter Ellis says:

    Thanks for this. There is actually quite a competitive market in New Zealand election forecasts given our humble size – at least three serious contenders that I know of. My own offering is at and includes links to the GitHub repository with the R and Stan code. I have one ad hoc tied-together-with-string model that is basically generalized additive models with house corrected polls, and one much more elegant and
    satisfying Bayesian state space model. Luckily they both say pretty much the same thing at the moment (which is that 90%+ chance of whichever side of politics forms a government they will have to negotiate with the populist/nationalist/social-conservative New Zealand First to do so).

  2. What’s with the piecewise constant model? I’d imagine a radial basis function approach would be easy, require only 4 or 5 centers, and give a nice smooth trend. Or a Fourier series… or a 4th order Chebyshev poly… or whatever.

  3. The impact of the Green’s and United First losing a leader plus Labour swapping for PR-glib with personality (whilst keeping identical policies) does appear to have changed voter intention as measured by the polls though. In the morass of polling, I am not sure anyone has asked about the changes in intention/behaviour (like the X-Box study) — have they? @Peter Ellis. It seems that the changes in our own wee micro-politkat illustrate some issues about the relationship between leader personality -v- policies x voter age x voter-traditional preference x SES. Will actual voting follow the public ‘Jacinda-mania’ social buzz (not to diminish at all that she is a remarkably competent politician) or will the preferences remain stable as one might expect after reading @Andrew’s link? We Hobbits are not much excited by adventure.

  4. Laura Kapitula says:

    My son has this t-shirt, if you are looking for some math/Gandalf humor :) I have no association with the seller, I just think it is a cute geeky shirt.

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