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Last updated 22 Mar 2021
Opinion polls enable people to express views on important issues and can inform politicians about the views of groups of people. Most polls are carried out by seven main organisations – Populus, Survation, Lord Ashcroft, YouGov, Ipsos Mori, Opinium, ICM. They generally take a sample of 1000–2000 people from 50–100 constituencies.
Opinion polls are carried out on a variety of issues. They may test policies for popularity, or they could test the approval rate for a political leader. But the central use of opinion polls is in the run up to elections, and in particular the Westminster General election.
The use of national election polls began with the 1945 general election. In general, opinion polls have proved accurate, particularly for the 1997,2001 and 2005 elections. However, the 1992 election, in which Labour was predicted to win by 1.3% but the Conservatives won by 7.6%, and the 2015 election, in which a tie was predicted by the Conservatives won by 6%, are major exceptions to this.
Polls can’t tell what someone will do on Election Day. They can only record what the person says they intend to do. People don’t always tell the truth even if the poll is taken just after they have voted (exit poll).
Opinion polls do not just stand alone apart from elections. Some argue that they can actually influence voting behaviour.
Polls showing a party leading before an election can have an influence on how people actually vote. This is called the Bandwagon Effect, when people vote for the party they believe is going to win. If a party is trailing in the polls, either people will switch to it or supporters of the leading party won’t bother to vote because they think their party has already won. This is called the Boomerang Effect.
Opinion Polls can also influence tactical voting. As it became apparent through polls that Michael Portillo could actually have a chance of losing his safe seat in Enfield in 1997, undecided voters and voters from other parties switched their vote to his opponent Stephen Twigg.
It is important also to note that exit polls if publicised on the day of an election – can influence voting behaviour. These polls are taken as voters leave the polling booths and ask how they voted. If their results are announced early it could mean a voter planning to vote late won’t go to vote if they think their vote won’t make a difference. This is not an important in the UK where we are all in the same time zone – but is important in the USA, where exit polls from the east coast come out 5 hours before some polls on the West Coast close.
The 2015 election saw a massive failure in the opinion polling industry, all of whom spent the election predicting hung Parliaments and pointing to constitutional chaos after the election. The British Polling Council has launched an inquiry into this, but indications are that they were not asking the right people, their methods are outdated and shy, reluctant and embarrassed Tories are not telling them the truth.
The exit poll that was published at 10pm on election night shocked everyone, with it becoming obvious that the opinion polls had been wrong. Professor John Curtice, who was in charge of the exit poll, had initially looked terrified, but gained confidence throughout the night, even noting that it might have underestimated the Conservative vote, which again was proved right as they went on to win an unexpected majority.