“In 2017, the number of young people who voted was the highest in 25 years”

That was the claim from a Labour party video tweeted by Jeremy Corbyn and John McDonnell this week, urging young people to head to the polls. But it’s based on shaky evidence.

Labour haven’t given us an official account of where the figure comes from, but FactCheck understands that it’s based on this 2017 Ipsos MORI report and this section of an article in the Financial Times from the same year: “Some 64 per cent of registered voters aged 18-24 are now thought to have cast a vote on 9 June, the highest share since 67 per cent voted in 1992.”

As the FT states, the findings are based on turnout among registered voters aged 18 to 24, rather than all adults of that age. This is a key distinction for pollsters.

The Ipsos MORI report in question actually recommends using the “all adults” figures rather than those based on registered voters, because the former are “more reliable and more meaningful”.

(The authors set out their reasons for preferring the “all adults” measure in this 2016 paper.)

The “registered voters” figure picked by Labour shows youth turnout at 64 per cent, but the “all adults” measure that the authors of the study prefer puts it somewhat lower at 54 per cent.

There’s another problem: the 2017 Ipsos report was never meant to be the final word on the matter.

The Ipsos authors warned at the time that “turnout estimates given below should be treated with particular caution, including taking into account the voter validation results from the British Election Study when these are published”.

In January 2018, the British Election Study (BES), considered the “gold standard” of political polling, published figures that led them to conclude the “youthquake” alleged to have shaken the 2017 General Election was a “myth”.

(We looked at the BES results in more detail at the time and discussed why these results are considered more reliable than other polls).

The BES found a much lower level of youth turnout than Ipsos MORI: 43 or 48 per cent of all adults aged 18 to 24, depending on which of the BES’ “all adults” measures you use.

There’s some debate about how conclusive the BES figures are, and the BES responded to their critics in a 2018 article. But even the Ipsos researchers suggest that they are likely to be more reliable than the 2017 Ipsos report.

Professor Roger Mortimore, the director of polling analysis at Ipsos, told FactCheck: “although we don’t think the evidence is strong enough to conclude that our figures are definitely wrong, there is sufficient doubt that we would not recommend relying on our figures rather than the ones that contradict them. Essentially, we don’t claim to know what the 2017 youth turnout was.”

But could Labour’s “25 years” claim still stack up?

The BES has changed its methodology, so we don’t have comparable data from them going back that far.

The best figures we can find that gesture in the direction of Labour’s claim come from the British Social Attitudes survey, which suggests 2017 could have been the highest General Election turnout among young people since 1997.

But it doesn’t go back to 1992, as Labour did, and using this figure would require us to overlook the fact that the turnout in the 2016 EU referendum was higher. And the Social Attitudes Survey is not the “gold standard” in this field.

FactCheck verdict

Labour said this week that “In 2017, the number of young people who voted was the highest in 25 years”.

The evidence to back up this claim is now out of date. The idea that the 2017 general election saw a “youthquake” was widely reported at the time – but it has been pretty much demolished by better data from the British Election Study.

We can’t find reliable evidence to back Labour’s wider claim that youth turnout in 2017 was the highest since 1992.

We’re grateful to Dr Christopher Prosser at the British Election Study for his help with this article.