A tale of two polls

Both TV networks released a poll tonight and the results are dramatically different. They are so far apart, that statistically it can’t be margin of error.

Let’s look at the four main parties:

  • Labour 42% in ONCB and 50.8%% in NRR
  • National 44% in ONCB and 37.4% in NRR
  • Greens 6% in ONCB and 6.2% in NRR
  • NZ First 5% in ONCB and 2.8% in NRR

You basically can’t reconcile these polls. One (or both) of them seem to be outside the 95% confidence interval, ie is the 1 in 20 “rogue” result.

The only other plausible explanation is that as the ONCB poll started a few days after NRR, Labour had a massive drop in support after those first few days. But the difference in dates is unlikely to explain the massive gap.

The polls ever show the direction of change differently. One has Labour down 6% and the other up 3.3%. National is up 4% in one and down 4% in another.

The NZ First result is also outside the margin of error. A 5% and a 2.8% result is outside the 95% confidence interval.

Bottom line is that at least one of those polls is wrong. They can’t both be right.

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