Reid Research runs a good poll. Pity TV3’s reporting of it doesn't match.

Duncan Garner’s report on TV3’s latest poll was poorly done. I usually think our TV political journos do a reasonable job despite their lack of familiarity with the statistical concepts they are reporting on. Not today.

(I should note here that some of what I am about to say is not the best of news for my favoured parties of the left. But I am saying it anyway. I am not a fan of the cognitive dissonance involved in believing any analysis that happens to show your team in a positive light. I would rather deal with the truth, even if it not pleasant to hear.)

The horse race
Garner reports that Labour has made up over eight points on National since their last poll, the largest one poll change this electoral term. While trivially true, this statement is silly and misleading. Why? Because the previous poll was probably wrong.

TV3’s September poll has National on 57.4 and Labour on 26.6, a gap of almost 31 points. That was a decidedly high-side estimate. Our Poll of Polls, which uses multiple polls to come up with a overall analysis of the political scene, estimated the National – Labour gap at around 24 points at that time. That TV3 poll represented the second highest estimate of National’s support all year, coupled with the second lowest estimate for Labour. It is little surprise that the gap narrowed from that level, because the earlier high level was likely due to sampling error. Of course, there was no mention of this possibility in Garner’s report. Last month’s poll was, like usual, taken as gospel. Which is pretty dumb.

Why the change?
Duncan does not explicitly speculate about what caused the shift in support. But in the opening paragraphs of his report on the poll, he does discuss National’s campaign launch in some depth, and in the broadcast version of the same report he discusses the first week of the campaign, with its various TV ads and policy announcements and campaign launches.

Which is all very interesting, except that the TV3 poll’s last day in the field was October 26th. Most of the interviews were actually done before the RWC final, and all were done before the big opening TV productions, before Labour’s superannuation / savings announcement, and before National’s campaign launch.

Linking any of those things with the poll result is lazy journalism. Viewers did not have access to the poll’s field dates, and it is the journalist’s job to present plausible explanations of the patterns the poll reveals. TV3 did not do that, instead implicitly inviting viewers to draw spurious links between unrelated events.

What if?
The frame many journalists are putting around recent polls is that if Labour surges, the Greens keep surging, and New Zealand First surges, then a coalition of the three parties has a shot at taking out a wilting “National + hangers-on” grouping. Here is why that kind of analysis is simplistic: The continued surge of the Greens hurts Labour’s ability to surge; and vice versa; and there is no sign whatever of the needed New Zealand First surge.

I posted recently about the relationship between changes in Labour’s vote and changes in the Green vote. When Labour picks up one percent, about half of it appears to come from the Greens, and half of it comes from elsewhere, most likely National. That pattern makes is really hard for both Labour and the Greens to surge at the same time unless the relationship between Labour and the Greens changes dramatically in the next four weeks. There is no sign of that. And one look at our Poll of Polls estimates for New Zealand First tells us they have been trending down steadily and are most unlikely to regain any seats this year.

So, where do we stand?
The left-right gap is around 16% with four weeks to go. The potentially-up-for-grabs parties look like winning around six seats. New Zealand First is a goner (I know, I know, but I’m calling it anyway.) That means for the left to have a chance, National has to drop below around 47% (give or take 1% depending on Epsom), with all that lost support going to the left, most likely Labour. The last time National polled that low was in early 2009, we estimate their support has been permanently above 50% since that time, and their trend is up, not down. The last time Labour and the Greens together polled 42% was in late 2008, and their combined trend is mildly down. But the campaign, short though it is, is just now underway. That is where we stand.