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Archive for September, 2014

Last night I published a Google Docs spreadsheet with a number of predictions for the 2014 Election.  Now the results are in I have updated it, and also added a few more sets of predictions from The RuminatorBen Kluge (@benkluge), and Grumpollie; and added the last single poll predictions from the various media outlets on the advice of Thomas Lumley.

On the advice of Thomas I have also adjusted the “number polled”, which is used to calculate the standard errors, from 1000 to 400, which gives an average chi-squared value of about 12.5 for 9 degrees of freedom (not too far off from what we would expect) and roughly agrees with Thomas’ estimate of 2 for the poll-to-poll variation.

We can then use the chi-squared values in column E to give a measure of how close each prediction was to the actual results.  I was a bit surprised to come out in first place amongst the pundits (chi-squared = 4.5), ahead of Gavin White (5.1) and Bryce Edwards (6.1).  David Cunliffe (5.3) is technically in 3rd spot, but I’m not going to count that because he left a lot of blanks in his predictions which I just filled in based on a scaled average of everybody else’s guesses, as explained yesterday.  The top performing poll-of-polls was William Bowe’s (5.8), followed by David Farrar’s Kiwiblog Weighted Averages (5.9).  A handful of pundits and polls-of-polls actually lost out to the 2011 Election results (chi-squared = 10.5), which is a bit of a surprise, but perhaps goes to show what an uneventful three years it has been for the major NZ political parties!

The average prediction in the table was about as useful as a randomly-sampled poll of about 290 people, which might not sound particularly good, but keep in mind that the performance of the average poll (typically with a sample size of about 900-or-so) was only about as useful as a randomly-sampled poll of about 260 people.

The only other point of note: even after (generously) rounding up the results to account for special votes every single one of the 23 predictions in the table will still have over-estimated the votes the Greens would win.  And for many that would be after correcting for the Greens under-performing relative to the polls at the last election.  Nobody on Twitter seems to have a credible explanation for why this happened.

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Punditry Is Fundamentally Useless – Nate Silver

A few people on Twitter and elsewhere have been making pre-election predictions for tonights results, so I thought it would be handy to have them all in one place so we can see how everybody performed.  I have created a Google Docs spreadsheet with everybody’s guesses.  Please feel free to download a copy and/or share it as you wish.

Fist things first: I made a previous reckons on Twitter, but I left out the “other” numbers, which I think will be quite high this year, so my updated predictions are as follows.

  • National 47.40%
  • Labour 25.70%
  • Green 12.00%
  • NZ First 7.00%
  • CCCP 3.50%
  • IMP 1.50%
  • Maori 1.20%
  • ACT 0.70%
  • United Future 0.20%
  • All other 0.80%

Not everybody in the spreadsheet made a full set of predictions; if there were results missing for any parties I simply took the averages of everybody else who made a prediction for those parties and scaled them so that the total numbers would add up to 100%.

The variance in the predictions is about what we expect if they were taken from a set of different polls with 1000-or-so respondents, so that number is in the spreadsheet at the top in cell B2.  This number is then used to calculate a “standard error” for each prediction (columns O-X) and measure how far off the actual results each prediction was (columns Y-AH).  These are then summed to get a Chi-squared value (NDF = 9), which is shown in column C.  This gives a measure of how close each prediction was to the actual results.

I will update the sheet when results are finalised.  In the mean time, if you know of anybody who has made a public prediction of the results that isn’t included please hit me up in the comments or on Twitter.

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Following on from previous posts, another short update on the iPredict stocks for National and Labour to win the 2014 election.

Daily average trade prices for National broke through the 80c barrier on 26 June, and Labour went below 20c on the same day.  The prices were reasonably stable around those levels for about six weeks until 13 August 2014 when the Dirty Politics scandal broke and National took a steep hit.  Average daily prices for National were below 70c for several days, and bottomed out at about 64c on 22 August, well before Collins’ resignation on 30 August.  The stocks have since rebounded, with National today trading for around 84c, an all-time high.

While there was obvious movement, most likely attributable to fear over the fallout from the Dirty Politics scandal, it was short lived.  As mentioned in the previous post the clock is running out for Labour, which needs to find some sort of game-changer, and there is less and less time left before the election for them to do so.

Graph of prices below:

Daily average trade price, 2014 election winner stocks on iPredict for National (blue) and Labour (red).

Daily average trade price, 2014 election winner stocks on iPredict for National (blue) and Labour (red).

Since Dirty Politics was released trading volumes and volatility are up significantly. During the last month there have been over 7,100 trades (National and Labour combined), and total volume was over 115,000.  Since opening on 26 October 2011 the total volumes traded are about 195,000 for National and 173,000 for Labour, so almost 1/3 of total volume traded in the last 3 years has been in the last month.  The stocks definitely aren’t moving about on small volumes.

Weekly volume, 2014 National election victory stock on iPredict.

Weekly volume, 2014 National election victory stock on iPredict.

Weekly volatility, 2014 National election victory stock on iPredict.

Weekly volatility, 2014 National election victory stock on iPredict.

The consensus seems to be that this isn’t going to be a particularly close election.

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