How accurately do exit polls predict election winners?

At 10pm on every election day, the first significant indication of the result is announced. Based on 'exit polls' conducted around the country as people leave the polling stations, the winners and losers are extrapolated - but with what degree of accuracy? Statista has gone back through the archives to compare exit poll predictions of the winning party and the amount of seats won with the actual result.

As this infographic shows, since the turn of the century the exit poll conducted for the BBC (recently in collaboration with ITV and Sky News), has held up fairly well in the cold light of the post-election day. In 2005, the projection of Tony Blair's third term win was completely accurate and, aside from the Cameron win in 2015 which was called short by 15 seats, the margin for error has been at or below five. There are examples of the exit poll being drastically inaccurate though. In October 1974, a 132 seat Labour majority was projected by the BBC, only for the result to be a far closer shave for Harold Wilson - a majority of three.

You can also find a more detailed look at the figures, here.