In the run up to polling day last Thursday, a large number of opinion polls were carried out, all aiming to estimate the public’s voting intention. The exact wording of the questions posed by polling companies varied, as did their approaches to weighting the responses, but in essence they all attempted to estimate the share of the vote each major party in Great Britain would receive at the General Election.
The results of these polls were broadly consistent throughout the campaign. But they were so different from the actual result for the two largest parties that the British Polling Council has launched an independent enquiry into the causes of the error.
So how different were the polls from the actual result? The chart below shows seven-point moving averages of the share of the vote for each party as estimated in opinion polls carried out by several major polling companies during the campaign period (from 30th March 2015), with the result of the 2015 General Election marked at the end of each series with a party-coloured X.