December 4, 2012

Making Nate Silver cry

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Stuff tells us

Polls have Labour closing in on Nats

A One News-Colmar Brunton poll released last night and taken a week after Labour’s leadership spat, saw the party’s vote lift 3 percentage points to 35 per cent, with the Greens up one on 13 per cent.

and later on

The One News poll of 1000 had a margin of error of 3.1 per cent.

 If you have been paying attention, you know that (a) the margin of error for a change is about 1.4 times larger than the margin of error in a single proportion, and (b) much more importantly, the useful thing to do with election polls is not to report each one separately, but to take some sort of average.

Did they have another poll? Well, the story goes on to say

 Meanwhile, a 3News-Reid Research poll, also released yesterday, showed Labour on the rise at 34.6 per cent, up 1.6 percentage points. The Greens improved 1.3 to 12.9 per cent, while National was down 1.8 at 47 per cent.

It doesn’t make as good a lead, because Labour was only up 1.6%, not 3% in this poll.  But if there are two polls, perhaps there are even more out there.

The poll of polls at pundit.co.nz shows a steady trend towards higher support for Labour, and a trend towards lower support for the Greens (with a bit more variation around the trend).  Their last update (including these two polls) put Labour up by 1% and Greens up by 0.2%.  But that would be less newsworthy.

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Thomas Lumley (@tslumley) is Professor of Biostatistics at the University of Auckland. His research interests include semiparametric models, survey sampling, statistical computing, foundations of statistics, and whatever methodological problems his medical collaborators come up with. He also blogs at Biased and Inefficient See all posts by Thomas Lumley »