Thursday's vote by the United Kingdom to leave the European Union was a surprise to many observers.
Seven of the last 10 opinion polls released showed a lead for Remain of between one and 10 percentage points; prediction markets put the probability of a Remain result as high as 90 per cent as recently as voting day; same-day polls taken of the British electorate showed a four-percentage-point win for the Remain side; and polls of British voters showed that they themselves thought the U.K. would vote to Remain.
How did a Leave vote happen?
Voters over 50
Throughout the entire referendum campaign, younger voters have said that they wanted to stay in the EU and older voters wanted to leave. The YouGov survey taken on voting day showed that 75 per cent of voters under 24 were voting Remain, while 61 per cent of those over 65 were supporting Leave.
Looking broadly at the polls, it seems like an important dividing line for opinion about the EU is 50 years of age, with those younger wanting to stay, and those older wanting to leave. To put it another way, voters who could remember a time before the U.K. joined the European Economic Community (a forerunner to the EU) in 1973 wanted out, while those who have lived in a united Europe their whole lives wanted to stay.
The other feature of voters over 50 is simpler and more important: They actually turn out to vote. Turnout figures by age do not yet seem available, but most estimates based on polling and census data suggested that older voters turned out at much greater rates than younger voters, with the gap the largest with the youngest – and most pro-Remain – age groups.
Labour's northern heartland
Areas toward the north of England have long been Labour Party strongholds, and while they were expected to vote Leave, they did so with much more aplomb than had been anticipated. For example, Sunderland, an area whose national and local representatives have been drawn overwhelmingly from the Labour Party for decades, voted 61 per cent in favour of leaving the EU.
The same story occurred throughout northern and historically industrial areas, like Warrington, Wigan and Middlesborough, where Labour-dominated areas voted to Leave, often by enormous margins.
This poses a problem for the Labour Party. It had officially endorsed a Remain vote and only a handful of Labour MPs supported the Leave campaign. While polls showed a majority of Labour voters likely supported the Remain side, Labour's failure to turn out Remain votes in some of its most historically popular areas suggest that the party's power to influence its traditional electorate is weakening.
Most polls expected either a close vote in Wales, or a small lead for the Remain campaign. Yet, by a margin of five percentage points, Wales joined England in voting Leave.
Wales' vote suggests that arguments about the economic benefits of the EU weren't successful. Since 2000, Wales has received billions of dollars of funding from the European Union. By voting Leave, Welsh voters signalled that arguments around the democratic health of the EU, or concerns about immigration and labour mobility, trumped the efforts of the Remain campaign.
Scotland was united in supporting Remain, with all counting areas showing a majority support for remaining in the EU. In areas like Edinburgh and East Renfrewshire, nearly three in four voters opted to Remain. Yet, turnout in Scotland was 67 per cent, nearly six percentage points lower than England's.
This isn't to say that a higher turnout in Scotland could have saved the Remain campaign. Even if all the voters who didn't turn out in Scotland had opted to stay in the EU, England's almost two-million vote majority for Leave would have overwhelmed Scotland's choice. However, combined with a higher turnout of younger voters, and an improved result in the north of England for Remain, the margins would have been much closer.
Ultimately, this strong Scottish vote to stay in the EU will pose the biggest problem for the United Kingdom. Scottish First Minister Nicola Sturgeon needs to convince just 5.3 per cent of Scottish voters to change their 2014 referendum "No" votes to ones in favour of independence.