In Brief

How accurate is the exit poll result?

Joint exit poll for BBC, Sky and ITV predicts big Tory majority

Britain is on course for a Conservative majority government, with the general election exit poll predicting a 86 seat majority for Boris Johnson’s party.

The Conservatives are likely to become the biggest party with 368 seats. Labour are in second on 191 seats, while the Liberal Democrats are third on 13 seats.

The Scottish National Party looks set to take home 55 seats, while the Green Party has retained its one seat. The Brexit Party does not look like winning any seats in its debut general election, according to the poll.

The poll is the last indication of how the election has gone before results start being announced across the country. While the exit poll has called the three out of the last four elections correctly, it did not accurately forecast the 2015 general election.

If the Conservatives do win a majority, it will be a huge boost for Johnson’s Brexit plans and could see a flurry of activity before Christmas as he seeks to hit his deadline of leaving the European Union before 31 January.

For all the latest results follow our election night live blog here

What is the exit poll based on?

The exit poll is based on thousands of interviews with voters as they leave polling stations across the country.

For this election, as with the previous three, BBC News, ITV News and Sky News will join together to produce a single exit poll.

Election guru John Curtice said: “The principal aim of the exit poll is to help viewers and listeners to navigate the initial hours of election night as the first results come in.

“By comparing the actual results with the forecast of the exit poll, we will be able to point to the political direction in which Britain is now apparently headed.”

How is the data collected?

Polling company Ipsos Mori will conduct tens of thousands of interviews at 144 polling stations.

As the i news site explains, “voters will be given a mock ballot paper and asked to complete it as they have just done inside the voting booth”. Statistical sampling methods are used to decide which voters are interviewed in order to provide a representative sample of the wider population. 

Analysts and polling experts then use a statistical model to make nationwide predictions based on the findings. According to the University of Warwick’s Department of Statistics, the methodology currently employed includes analysis of the results of the previous elections and of local-level data from previous exit polls; measuring electoral change in a multiparty contest (rather than a two-party election); and statistical modelling.

How accurate is the exit poll?

In recent years, the exit poll has been fairly accurate, predicting the result of the election correctly in 2017 and 2010. However, the poll predicted a hung parliament in 2015 - when in fact David Cameron had won the first Conservative majority since 1992.

According to the Warwick University team, a “House of Commons majority prediction that is within 20 seats of the actual outcome is a reasonable aspiration from a well-conducted exit poll”.

With this year’s election expected to be tight, that margin of error could be the difference between a Tory majority and another hung parliament.

Or to put it another way, while the 10pm release of the exit poll should provide a fairly clear idea of who has won, it may be worth staying up a little later to find out for sure.

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