America does exit polls differently to the UK - here's how and why

There are two main differences between election coverage in the UK and the United States.

Last July, at 10pm, Sky News' exit poll graphic predicted a Labour landslide and a massive defeat for the Conservatives.

Confirmation of this forecast was a long time coming since constituency results are only announced by local returning officers once all votes have been counted.

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Americans do things differently and for good reason. Polling stations close much earlier in the east than they do in the west. When voting has hours to go in some states, they've already started counting elsewhere.

There is a "wait for it" moment when voting closes in west coast states and the broadcasters can reveal the national exit poll headline, but this won't tell us the winner.

Instead, it will tell us the types of people who have voted for Harris or Trump and the issues that dominated the outcome.

So far, one-nil to the UK, I think. But, here comes the next bit.

Instead of postponing announcements about votes until every last one has been accounted for, each state then begins releasing figures as and when votes are being counted.

And they do so in such a way where we can compare this time with previously. Not for them declarations in sports halls with dodgy microphones but rather running tallies for precincts (think our local council wards) and counties (ranging from tiny to huge).

It's these data that US broadcasters such as NBC will use to "call" each state's vote for president. The television networks are big players in the US election drama.

Over 160 million votes will be cast in the election, more than five times the number cast in our general election last July.

And while the outcome of our election was in no doubt once the broadcasters' exit poll revealed Labour had won a landslide majority, that will be far from the case in the battle for the presidency.

As in the UK, a consortium of US broadcasters, comprising NBC, ABC, CBS and CNN, form the national election pool.

This commissions the consumer research company, Edison Research, to survey voters in over 600 polling places as people exit their polling station.

The survey also includes telephone interviews with people casting a ballot before 5 November. Once completed, the US exit poll will have obtained responses from over 20,000 voters, a similar number that were collected for the general election.

Two surveys of voters, therefore, but now important differences in their purpose become clear.

The UK version is entirely focussed on predicting the distribution of seats among the competing parties and, thereby, the winner and its likely House of Commons majority. Over recent elections it has proved pretty good at achieving this task.

By contrast, the US version is much less concerned about predicting the winner (and there are very good reasons for taking this approach) and more interested in the campaign issues that mattered to voters, how they viewed the candidates and what factors motivated them to make their choices.

The survey identifies key demographic characteristics for each respondent - men or women, age, ethnic heritage, and educational qualifications.

Combined with questions relating to their choice for president this time around, their usual partisan preference, Democrat, Republican or none of the above, the survey data enables a considered and detailed analysis of what kinds of voters made what kinds of choices and their reasons for doing so.

Broadcast organisations, including Sky News, will use the 2024 exit poll to highlight differences between men and women voters in relation to the abortion issue.

The poll will also show how the economy ranked among voters and whether Donald Trump's stance on low taxation gained or lost him votes among different social groups. Did Kamala Harris's association with the Biden administration and the challenges of illegal immigration prove to be a positive or a negative in her bid for the White House?

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All very interesting, but aren't we all tuning in to see who's won? While the US exit poll can, in theory, be used for this purpose it is unwise to do so in what is proving to be an extremely close race.

Sky's tracker of national polls shows the Democrat blue line and the Republican red line moving ever closer together but with Harris currently marginally ahead. But even if she loses the national vote, the polls would still be within the margin of error.

Of course, she could yet win more votes than Trump and still lose the election, as Hillary Clinton discovered when she lost to him in 2016. Winning votes is necessary, but it's where those votes are and the available number of electoral college votes that matters the most.

Trump beat Clinton because his votes were better distributed than hers. History could be repeated.

Releasing precinct-level voting numbers as counting progresses is essential to US election coverage. The national election pool employs over a thousand researchers to collect votes from each of the 50 states.

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Additionally, NBC News will augment these figures with more detailed analysis prior to making its call for each state and the electoral college votes for Harris or Trump. The first to reach 270 college votes wins.

Professor John Lapinsky of Pennsylvania University leads NBC's decision desk.

Although the broadcasters have pooled resources to bring us the exit poll, each will independently analyse the actual voting figures as they become available.

Lapinsky and his team on behalf of NBC will call the state for either Harris or Trump only when they are satisfied that the leading candidate's vote is sufficiently large that he or she cannot be overtaken.

This a big moment for each broadcaster, especially when the race is likely to be close and where social media may be playing a significant role in stoking accusations and counter-accusations of a fraudulent election.

With so much at stake, these decisions will take time and patience.

Our July election was done and dusted in time for the breakfast bulletins. It could be days of counting, recounting and legal appeals before we know the winner of the 2024 presidential election.

(c) Sky News 2024: America does exit polls differently to the UK - here's how and why