03/11/16

US ELECTION POLLS V UK POLLS

A matter of opinion: statistics reveal US opinion polls are 57% more accurate than UK predictions

With Americans set to elect a new President next week, statistics show that US opinion polls are on average 57% more accurate at predicting the winner than similar polls in the UK.

When comparing the final opinion polls on the eve of the last ten national elections in each country, US predictions are only 2.94 percentage points different to the final result, whilst UK predictions were on average 4.62 points off in their final analysis.

The study, conducted by spread betting company Spreadex, looked at the past ten US presidential and UK general elections with results showing a clear difference between the accuracy of pollsters on either side of the Atlantic. The study found that:

• US polls have, as an average, correctly called the winner prior to polling day in every single presidential election since 1976
• UK polls are less accurate, with them failing to predict the wrong winner on two of the last six occasions, in 2015 and 1992
• Final polls have been wrong by more than three points only four times in the last ten US elections
• In two of the last four UK elections, final polls were more than six points wrong each time

As far as accuracy is concerned, US polls were closest in 1984, with predictions only 0.27% wrong on Ronald Reagan’s margin of victory over Walter Mondale. Their worst prediction came four years earlier when Reagan beat Jimmy Carter, although on that occasion they called the correct winner and only underestimated the level of victory. In contrast, UK polls failed to predict the eventual winner in the Conservative victory of 2015 - having forecast a tie - and in 1992 when a predicted slim victory for Neil Kinnock’s labour actually led to a John Major victory by a 7.5% margin.

The closest call of recent years in the UK was in 2005, when predictions were within 0.2% of the final result. The worst prediction in the past 42 years came in 1987, although on that occasion polls did correctly forecast the winner, only underestimating Margaret Thatcher’s eventual 9.3% winning margin over Kinnock.

UK voters will be familiar with inaccuracy in opinion polls away from general elections in recent years. In June earlier, the final ‘poll of polls’ predicted a 4% win for the Remain Camp in the EU Referendum, whilst in Scotland polls correctly predicted the final outcome of the 2014 independent vote, but not the margin of victory. In the final result, ‘yes’ voters accounted for 10.6% of the vote, although the opinion polls failed to forecast higher than a 5% margin.

Connor Campbell, Financial Analyst at Spreadex, said of the findings, “UK voters are used to opinion polls not always being accurate, but on the other side of the pond it’s an entirely different story. The predictions seem to be correct each and every time, with sometimes near-pinpoint accuracy.

The US election is proving to be one of our most popular political markets ever and we are seeing some huge bets being placed, including from one punter who has staked £200,000 on a Trump victory. With the U.S. in the closing stages of the campaign and the polls seeming to change every day, it should make for a very interesting few days in the lead up to the election.”

The study looked at the polling data from 16 different polling organisations in the US and UK, across 20 elections between 1974 and 2015, comparing the average prediction in final set of polls against the eventual result.