What is an exit poll? How result will be predicted on 2019 general election day

By Charlie Duffield

Prime Minister Boris Johnson’s plan for a snap general election was given the green light on October 29, and will be the first December election since 1923.

This time around it’s deemed the ‘Brexit’ election, and therefore thought to be one of the most unpredictable in years.

Will the exit poll manage to accurately predict the outcome? We’ll find out in five weeks’ time. Meanwhile, here’s everything you need to know about exit polls and how they work.

The UK will go to the polls for a snap general election on December 12, 2019. (Photo: Lindsey Parnaby / AFP via Getty)

What is an exit poll?

An exit poll is a survey of a small fraction of voters.

Exit polls are a huge undertaking, with thousands of interviews taking place with voters outside of polling stations, after they have cast their vote.

Voters arrive at a polling station in Dublin to cast their vote in the European Parliament election in May 2019. (Photo: Artur Widak/NurPhoto via Getty Images)

Read more: What is a hung parliament and will there be one after the 2019 general election?

Individuals are asked via an anonymous poll which party they voted for, alongside their age, race and gender. The form is then placed in a ballot box.

An exit poll is mainly used to estimate the turnout and electoral swing, which is the extent of change in voter support compared to the previous election - but data can’t be released before polls have closed.

The polling focuses on more marginal and swing seats, as these are the most important seats in determining the election result.

Exit polls differ from regular voting intention polls, as regular polls ask who you intend to vote for, whereas exit polls ask who you actually voted for on election day.

In 2015, the general election exit poll was derived from 20,000 interviews with people at 140 individual polling stations.

Read more: What is tactical voting and is it allowed in UK general elections?

What time are exit poll results usually announced?

Huw Edwards will present the exit polls during the BBC’s election night coverage, instead of the long-serving David Dimbleby.

Results of the exit poll are typically revealed at 10pm on the day of the election.

Exit polls in the 2017 general election projected that Theresa May's ruling Conservatives would be the largest party, but that they may fall short of a majority. (AP Photo/Frank Augstein)

How accurate are exit polls?

Exit polls have been used to predict general election results in the UK for decades. However, they’re not always foolproof.

In 2010, the exit poll was right and accurately indicated a hung parliament, but in 2015 it didn’t predict a majority for the Conservatives. In 2017, the exit poll shockingly revealed that Theresa May was set to lose her majority - and indeed, it was accurate as we were saddled with another hung parliament.

The polling stations where exit polls take place are selected to provide a representative sample of the wider population. Therefore, the poll is undertaken to ensure it is as reflective as possible of the voting patterns and demographics of the entire population.

A general view of a polling station at the White Horse Inn in Priors Dean, Hampshire, also known as the 'Pub with no name', as voters head to the polls for the European Parliament election. (Photo by Andrew Matthews/PA Images via Getty Images)

However, essentially an exit poll is just a forecast from sample data, and there is still margin for error. This margin usually only accounts for a handful of seats - but importantly, over the last few years, it’s only taken a few seats to decide the winning and losing party!

In three out of the last four elections (2005, 2010 and 2017), the exit poll has been right. In 2015, the exit poll incorrectly forecast a hung parliament, and pollsters were criticised to such an extent that the British Polling Council announced an inquiry into the discrepancies.

They later showed the likely cause of the discrepancy was poor survey techniques and problems with the manner in which sampling and weighting took place.

The release of the exit poll is always a nail-bitingly tense moment, offering a teaser of the potential future fate of the country after a frantic day of voting.

Time will tell if the pollsters hit the mark again this time round in December.

Read more: When will we find out the result of the general election?

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