But in the last decade and a half the exit polls have become much more accurate.
Here are the figures for 2001.
ITN: Wrong by 8
BBC: Wrong by 10
From 2005 onwards there has been a joint exit poll, firstly commissioned for ITN and the BBC, and then, from 2010 onwards, for Sky too. Its record has been much better.
2005
Wrong by 0. It predicted a Labour majority of 66, which Labour got.
2010
Wrong by 0. It said the Tories would be 19 short of a majority, and they were.
2015
Wrong by 22. It said the Tories would be 10 seats short of a majority, but they got a majority of 12.
October 1974
ITN: Wrong by 12
BBC: Wrong by 132
1979
ITN: Wrong by 20
BBC: Wrong by 29
1983
ITN: Wrong by 28
BBC: Wrong by 2
1987
ITN: Wrong by 34
BBC: Wrong by 76
1992
ITN: Wrong by 62
BBC: Wrong by 70
1997
ITN: Wrong by 20
BBC: Wrong by 6
But in the last decade and a half the exit polls have become much more accurate.
Here are the figures for 2001.
ITN: Wrong by 8
BBC: Wrong by 10
From 2005 onwards there has been a joint exit poll, firstly commissioned for ITN and the BBC, and then, from 2010 onwards, for Sky too. Its record has been much better.
2005
Wrong by 0. It predicted a Labour majority of 66, which Labour got.
2010
Wrong by 0. It said the Tories would be 19 short of a majority, and they were.
2015
Wrong by 22. It said the Tories would be 10 seats short of a majority, but they got a majority of 12.