1 election where the final polls got the result badly wrong. Each deep dive sets out what the polls said, what happened, what the official inquiries and the pollsters found, what our own data shows, and what the pollsters changed afterwards. Every one of these misses is in the record our forecasts learn from.
How far out the final polls were
The error on the lead between the top two: the final polls' average against the result, in points.
The last polls before the blackout had Bersani's centre-left about 5 points clear and the M5S on 15%; the centre-left won the Chamber by 0.4 points and the M5S took 25.6%, the largest single list. Every pollster understated the M5S and overstated the PD, through a new party with no past vote to weight on, reluctant centre-left switchers and a late surge inside the 16-day blackout.
For each country we measure how far the final polls missed at past elections. We take half the average miss off today's polls only where that would have made past forecasts better, testing each election without knowing its result; elsewhere the polls stand as published. Every forecast then runs thousands of simulated elections with polling errors the size of these, so a miss like the ones above is inside our ranges, not a surprise. Polls against results, every election · Our forecast record · Pollster leaderboard
Italy · 24 February 2013
4.9 pts