General election 2017: The problem with the polls

Labour support has surged in the past three weeks, narrowing the gap with the Tories and raising hopes and fears alike that Theresa May will be denied the large majority predicted when she called the snap election. So tight is the race said to be, some polls are even predicting a hung parliament.

But what if they are wrong? They were at the last election, an error attributed to an over-estimation of the number of young people who would vote.

Turnout among younger voters will again be crucial, says the Financial Times. Pollsters ICM found "nearly three-quarters of 18 to 24-year-olds say they will back the Labour party on 8 June, compared with just 15 per cent of over-65s".

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Since the campaign began in April, more than 1.5 million under-35s have signed up to vote, the Daily Mirror reports, but they are also the demographic least likely to make it to the polls.

Fresh statistics from the National Centre for Social Research suggest only 53 per cent of those under 30 are certain to cast their ballot. In the 2015 general election, 18 to 24-year-olds were almost half as likely to vote as those aged over 65, says Politico.

A last-minute upset is not beyond Labour's grasp, but it will be "hugely dependent on the 8 June election bucking a well-worn trend".

Another consistent problem with UK general election polling has been the "historical overestimation of Labour support", says Anthony J Wells, political director of YouGov.

In the 2015 general election, pollsters boosted Labour's vote share by between three and four per cent, "as opinion polls have tended to since 1959", says Ipsos Mori boss Ben Page in The Times.

This is down to unrepresentative sampling and overstated estimations of turnout, which polling firms have attempted to redress with a variety of changes to their methods to try to correct.

We will see whether pollsters have been able to correct their tendency to overstate Labour support on 8 June, says Wells, "or indeed, whether they've gone too far and resulted in a pro-Tory skew".

US pollster Nate Silver writes on FiveThirtyEight that UK polls have been "both highly volatile and fairly inaccurate".

He writes: "Pollsters are under a lot of pressure to get the answer right, and they're constantly tinkering with their methods. But there are a lot of moving parts and there's only one election every few years for them to test their methods upon.

"If they don't make any changes, pollsters might duplicate a previous mistake. But they also might overcompensate for one-off circumstances that won't replicate themselves again."

It is a "timely reminder that polling is an art, not a science", writes Anne Perkins in The Guardian.