What formula could we best use to judge the winner of election predictions?

There have been some interesting threads started by Jonathan Chance on election predictions (such as here and here).

Let’s assume we take only the top 3 predictions for each poster (to keep the maths simpler.)
For example, we could have predictions like these examples for Iowa:

Poster A
Trump 38%
Cruz 20%
Rubio 15%

Poster B
Cruz 30%
Trump 25%
Bush 20%

The actual result was:

Cruz 28%
Trump 24%
Rubio 23%

So we can make a formula for each poster’s prediction based on (say):

  • the difference between predictions and actual for the top three candidates (always take as positive)
  • a ‘penalty’ for each top three candidate missed (I’ll use 25%)
  • then take the total of the above two and subtract from 100 (just to give a positive result)

Using my formula, the above two predictions would score:

100 - (14+8+8) = 70 for Poster A
100 - (2+1+25) = 72 for Poster B

So B does slightly better, despite missing one of the top 3.

What do you think of my formula?
Have you got a better one?!

If I get enough interest, I’ll have a go at ranking the posters for each State. :cool: