This latest election “debunking” doesn’t come offby Peter Kellner / January 30, 2018 / Leave a comment
As a rule I enjoy attempts to debunk conventional wisdom. It is not done enough. However, I am not sure the authors of the latest such exercise have proved their case.
This is how the authors of the British Election Study (BES) have upended one of the most widely held beliefs about last year’s general election:
“The Labour ‘youthquake’ explanation looks to become an assumed fact about the 2017 election. The Oxford English Dictionary even declared ‘youthquake’ their word of the year. But people have been much too hasty. There was no surge in youth turnout at the 2017 election.”
Before going further, I must express my huge admiration for everyone who has made the BES such an important resource for political scientists for more than half a century. That includes the authors of the latest study, most of whom I know and respect.
However, their latest pronouncement goes way beyond what their data can support. They base their analysis on two post-election, face-to-face surveys after the 2015 and 2017 general elections. Their sample size in 2015 was 2,987; in 2017 it was 2,194. These are larger samples than in most individual polls conducted for the media—though some research reported by the media involved far more people (such as the 50,000 polled weekly by YouGov, which formed the basis of their prediction of a hung parliament, and their indication that the Conservatives were in trouble in Canterbury and Kensington).
Where the BES team skate on thin ice is when they seek to draw precise conclusions from small sub-groups. They derive their main conclusion from the 1,400 respondents that they have crossed-checked against the electoral register, to confirm whether those who say they voted actually did so. This is a valuable exercise which, by definition, campaign polls cannot do, because people have not yet voted (or abstained). Even doing so after the election is expensive and time-consuming. So, congratulations BES, for doing this.
Here are the figures that underpin their conclusion that turnout did rise significantly among 25-44 year-olds, but actually fell sharply among the under 25s, and changed little among the over-44s:
It is the figures for the under 25s that have caused such a stir. The figures for all the other age groups are broadly in line with what pollsters reported months ago.
Here’s the problem. BES interviewers questioned, and confirmed the turnout answers, of only 157 under 25s in 2015 and 109 in 2017.
Data obtained from such small subsamples are subject to large margins of error. The normal formula indicates that the reported turnout for this group could have been eight points adrift of reality in 2015 and almost ten points adrift in 2017. Applying those figures to the BES data, we may deduce that the correct figure for the turnout of the under 25s was 41-57 per cent in 2015 and 34-53 per cent in 2017. (Technically, we would expect the true figure in each election to be within those wide ranges 19 times of out 20; but one time in twenty, a perfectly well conducted survey would be beyond even these limits.)
On those figures, we can say nothing sure about the change in turnout among under 25s in these two elections. (By the by, I am amazed that the BES report data with a near-10 point margin of error to a decimal place. This purported precision is utterly spurious.)
In fact, the true margins of error are greater than that—though how much greater is impossible to calculate. The formula used above assumes a perfectly designed sample with a 100 per cent response rate. BES’s sample design was fine; but its response rate was below 50 per cent. Nobody can be sure whether the voters they did not reach behaved like the voters they did manage to interview.
My own guess is that all pollsters, including the BES researchers, have huge difficulty accurately measuring the behaviour of students in particular. Some are registered at their parents’ address, some at their university, some at both, some at neither. We also know that many registered in the weeks leading up to last year’s election. If more students were on the register last year than in 2015 (including those who converted from one-address voters to two-address voters, to make sure they were able to vote on the day), then it’s possible that the number of students who voted last year was higher than in 2015, even if their turnout percentage rate was the same, or even lower.
So what is the truth? In some constituencies that a) were hard fought (for example because they were marginal, or had changed hands in 2015), and b) contained a higher proportion of students, turnout rose sharply: by nine percentage points in Cambridge, for example, seven points in Canterbury and Bristol West, and five in Brighton Pavilion and Norwich South. In other, usually safer, seats with large student populations, the picture is more mixed.
These examples do not prove that a “youthquake” happened; but the BES data do not disprove it. For the moment, this particular piece of conventional wisdom survives to fight another day.
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