With nine months to go, how much can opinion polls tell us about the general election on November 7? Short answer: not much.

Based solely on polls, no one could have predicted the past three elections this early in the year they were held. Trends shifted over the subsequent months, and events (especially COVID in 2020) intervened to shake things up.

Each poll is a snapshot of past public opinion – and it’s out of focus, due to statistically inevitable sampling error. A sample of 1,000 people won’t exactly resemble the whole eligible population, and the percentage of “undecided” voters often goes unreported.

Researchers have an incentive to produce results that are as accurate as possible, but statistical variance happens. Each poll is an estimate. And a small variation between two polls by one or two percentage points is “noise”, not “signal”.

We get a picture of how party preferences have shifted by looking at trends across a number of polls. But past trends aren’t a sound guide to future trends.

The Research Association New Zealand’s Political Polling Code requires that projections of the numbers of seats for each party “should state that polls do not predict – they measure a point in time”.

I’d add that no one can........

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