Despite some excitement in individual polls, the polls as a whole show National still well above 50%, and New Zealand First still a long way below 5%.

There have been four polls published since we updated the Poll of Polls last Monday. Our updated estimates show continuing trends against National and Labour (each of whom drop about half a point this week), and in favour of the Greens (who gain most of a point). We now estimate the Greens at almost 11% support and climbing. As I noted last week, some of the Greens’ longer term prospects rest on whether they can get their 12th to 15th ranked MPs into Parliament, given those particular candidates’ possible role in broadening the Greens’ support coalition in suburban New Zealand. That will be one of the most interesting aspects of election night.

Results for New Zealand First are mixed across the four polls this week, with a range from 2.2% to 4.9% estimated support. Our overall estimate is that New Zealand First’s support is little changed from last week, up a touch to 2.8%.

The other incumbent parties continue to cement their cellar-dweller status.

Even though the election is in five days, our estimates are based on polls with sampling periods centered at least 12 days before election day. We may see one or two more polls this week, but even those will likely be based on samples centered a week or more before polling takes place. Given that there are some fairly strong trends in parties’ support during the campaign, this could cause any polling-based estimate, including ours, to miss some late shifts in public support.

Another way to project Saturday’s results is to run some simple regressions based on all campaign-period polls (weighted by sample size). I did this for the four largest parties, and the results are charted below.



This kind of setup is based on an assumption that the linear trends we have observed in the campaign to-date will continue unabated up to election day. There is always the possibility, of course, that such as an assumption will be wrong. Maintaining that assumption, however, we are able to not only make projections, but also estimate the probability of some important events.

New Zealand First makes 5%?

Using the analysis above, we project that New Zealand First will get 3.8% of the vote. We can also project with 95% confidence that the party will get between 2.3% and 5.2% of the vote. Importantly, we project that there is only a 4% probability New Zealand First will get more than five percent of the vote.

National makes 50%?

We project that National will get an absolute majority of the vote, but a pretty small one (50.8%). Based on this analysis, we think there is a 74% chance that National will get over 50% of the vote.

Readers should note that these fact-based projections are both very different from the predictions on ipredict of these events. As at late Sunday, ipredict thinks there is a 30% chance that National will get a majority; we say 74%. And ipredict thinks there is a 48% chance New Zealand First will break 5% even though no recent poll has shown them over 5%, plenty of polls have shown then a long way short, and their moment in the sun was probably last week rather than this week coming. We say that probability is much lower, 4%. This difference illustrates one of the risks in basing projections on market behavior: The assumption that markets are uniformly efficient and that all market participants are rational. Both those assumptions have been falsified many, many times.

In both of these important areas, the projections are saying the same thing as the Poll of Polls. National will be able to govern alone; and Winston will not return to Parliament. The difference between the Poll of Polls and the projections, which amount to 2.5 points for National, 3.5 for Labour, and almost four points for the Greens, are interesting analytically and important to some MPs and potential MPs, but are not important for the broad result.

(One important warning about the projections in the charts above is that they are out-of-sample predictions, and so are subject to more than usual error. Exactly how much extra error we should add in is uncertain, which is another way of saying that you should take the projections with a grain of salt, over and above the sciency-sounding 95% confidence intervals. In addition, any additional polls this week could make a large difference to these regression-based projections.)

Comments (12)

by Danyl Mclauchlan on November 21, 2011
Danyl Mclauchlan

What does your fancy regression analysis show ACT at? If they did get Epsom, would they get one or two MPs?

by Rob Salmond on November 21, 2011
Rob Salmond

@Danyl: OLS wth n=14: fancy, huh! This way of doing it projects ACT at around 1.7% (very similar to what they showed this week in all four polls), so if they win Epsom there is certainly a caucus of 2, and they are within striking distance of 3.

by Tim Watkin on November 21, 2011
Tim Watkin

That's a hideous scenario for Labour. I wonder whether the two leaders' debates will put the spotlight back on the big two and nudge a bit of vote back Labour's way.

And I wonder how the 'wisdom of the crowd' will respond to discussion of National governing alone.

by Rob Salmond on November 21, 2011
Rob Salmond

@ Tim: I think there could easily be a shift in the trends this week, as the focus goes back on the large party leaders. One of the mild shortcomings of any fact-based projection is that it cannot account for what we think will happen tomorrow.

by SPM on November 21, 2011
SPM

Enough of the scare-mongering about National 'governng alone': that simply means that a majority of New Zealand voters, after an election campaign where its policies have been well aired, decided it deserved their vote.  Democracy in action, I would say.  Why are you not as concerned about the unknown and as-yet-unknowable compromises that would be involved in a Labour-NZFirst-Mana-Greens coalition?

by Rob Salmond on November 21, 2011
Rob Salmond

@SPM: I do not think I was scaremongering. I did not even use the term "governing alone," or make any comment about the policy settings of any potential right-leaning government. I simply told you, without editorializing, what the polls are saying, when analyzed two separate ways. The reason I did not speculate about possible post-election compromises in a Labour-led coalition is that this post was about polls instead. But thanks for playing.

by tussock on November 21, 2011
tussock

Still no Mana party on your lists. Seems like they'll be in paliament with some number of MPs, and they're hoping the polls underrepresent their poor-ass voting base (and that they can cause a higher turnout based on a wider range of policy on offer).

Yeh, I know, hope, but what do the polls say?

by SPM on November 21, 2011
SPM

Sorry Rob, referring to Tim's comment, not your article.  Your article is straight bat stuff.

by Rob Salmond on November 21, 2011
Rob Salmond

Fair enough. Thanks for clarifying, SPM.

by Tim Watkin on November 21, 2011
Tim Watkin

SPM, read my reply to Deborah. How is looking at the implications of a possible scenario (based on three years of consistent polling) scare-mongering? Especially given I first hypothesised about it months ago.

I admit that it makes me a little nervous given our lack of constitutional constraints, but more to the point I'm suggesting that, based on my experience and thinking, it may influence how people vote.

That's my analysis and it's what I do on this site. At least mine is fact-based. You seem to be unaware that Goff has repeatedly ruled out Mana. So who's scaremongering again?

by James Green on November 22, 2011
James Green

Rob - nice analysis. I wish I'd had the balls to call this yesterday, but seeing as Roy Morgan are promoting themselves now, it's really interesting to see such a major divergence between pollster

http://distractedscientist.wordpress.com/2011/11/22/roy-morgan-predictin...

by SPM on November 22, 2011
SPM

Tim, I read that thread as well.  Plenty of administrations in New Zealand's history have 'governed alone'.  My curiousity is around whether you are concerned about any administration doing the same under MMP? Or just the possibility of a National administration; or rather, this National administration, doing the same? Because those are two different concerns, in my view: one legal and one party political, if I can put it that way and I am not entirely clear fro your article and comments on where your concern lies.  FWIW, I understand the constitutional law issues and Andrew Geddis has pointed out that New Zealand does have an effective constitutional law framework, if not an actual 'constitution' in one document.  Some conventions are entrenched, there would be a heavy political price to pay for changes; and ultimately no one is talking about changing the constitution - even your point in the other thread was illustrated by reference to a social welfare policy, indicating to me at least that is where your concerns lie: not the theoretical ability of an administration in an MMP environment to implement policy on which it did not receive a mandate.

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