ACT in Wellington

Lindsay Mitchell has helpfully scanned in the regional breakdowns of the Fairfax poll. Lindsay is encouraged by ACT getting 6% in Wellington.

Now it is a good result, but one can read too much into it.  Regional breakdowns of National polls have high margins of error.  In fact I think these should always be published also.

Now the nationwide sample was 1,007.  Based on the fact that Wellington’s population is around 10% of NZ, I’d estimate their Wellington sample was around 100 people. Now this means a maximum margin of error of +/- 10.1% for those Wellington results.

Now ACT scored 6%, and the maximum margin of error is for a score of 50%, so what is the margin of error for a score of 6% in a sample of 100? It is +/- 4.8%.

So with 95% confidence ACT is between 1% and 11% in Wellington.  I suspect it is not at the very low end, as ACT have traditionally done relatively well on the party vote here.