On Friday I published my weighted poll of polls, so it's only fair for me to face up with how it actually went.  This is based on the election night vote, and my previous calculations are based on the final vote (including special votes).  It's unlikely that special votes will change the result significantly, but history suggests that National and NZ First will end up down slightly on the election night results, and Labour and the Greens up slightly.  I'll come to that in a minute.

Firstly, I'll give you what I wasn't allowed to give you on Friday - the final results for our own UMR poll.  Of course people are going to say that we've played with the results to fit the election night numbers, but these exact numbers were shared with our client on Friday.

There's a lot of attention on political polls at election time, and a lot of people claiming that the polls are becoming less and less accurate.  It's true that polling companies face growing challenges in getting our polls accurate, but it is something we put a lot of effort into.  I thought it was worth looking objectively at the public polls over time to see whether they really are becoming less accurate.

Here are the basic tools I'm using for judging accuracy:

1) The final result for every public poll published in New Zealand between 1999 and 2011 (i.e. the last result before election day)

2) The party vote for the four largest parties on average across that time period (National, Labour, Greens and New Zealand First)

3) The difference between what the polls said and what the actual result was.

Now, I'm aware that the Alliance (1999) and ACT (1999 and 2002) have made guest appearances in the top four occasionally, but I thought it simplest to use the same parties for all five elections.

I've measured the difference between the polls and the actual result using what I term 'net error'.  That is, the sum of the absolute values of the differences between the polls and the actual result for the parties concerned.  If, for example, a poll picks National to get 48% and Labour to get 26%, and the actual result is National 47% Labour 27%, then the 'net error' for National and Labour is 2% (made up by 1% for National and 1% for Labour).  A perfect poll would therefore have a net error of 0%.

The polls I've used are:

The blog I wrote a few months ago on political polls and election results (here) has generated a lot of debate and several media appearances.  The most recent of these screened last night - it was Maori Television's new show Media Take (hosted by Russell Brown and Toi Iti).  I'll start by thanking Russell for inviting me on the show - it's always fun to debate these issues and I think Media Take in general is going to be a really interesting show.  

One of the things Russell asked me to comment on was Paddy Gower's report on a TV3 poll, which had New Zealand First on 4.9%.  TV3 based their analysis on New Zealand First being below the threshold.  Quite apart from the fact that New Zealand First always does better on election day than they do on the final polls (which could be as much due to votes shifting during the campaign as to polls being accurate), to suggest that a poll result of 4.9% means that any party is definitely below the 5% threshold is statistical nonsense.

As I said to Russell, shifting from 4.9% to 5.0% in a poll of n=1000 requires just one person to change their minds.  Alternatively, it requires one of the people who were supporting another party to be out at the time the phone rang, and someone who supports New Zealand First to be home at the right time.  That's why we talk about probability and margins of error.

A colleague recently sent me an American poll on visits to the dentist, and we thought it'd be interesting to see how New Zealanders compared.  Our poll covers a representative sample of n=1000 New Zealanders aged 18 years or older, and was conducted between April 29th and May 12th 2014, while the American survey is from the Gallup-Healthways Well-Being Index 2013 which covered 178,072 American adults.

The basic question was very simple: "have you visited a dentist in the past 12 months".  The results, however, are perhaps surprising.

• 52% of New Zealanders say they have visited a dentist in the last 12 months.
• By comparison, 65% of Americans say they have done so.

Gallup's analysis (available here) focused on the fact that one third of Americans hadn't been to the dentist in the last year, clearly because the writer saw this as surprising and newsworthy.  What would they have made of the fact that almost half the New Zealand population (47%) say they haven't visited?*