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 Ruminator, Ben 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.