Tremors but no youthquake: Measuring changes in the age and turnout gradients at the 2015 and 2017 British general elections

In the aftermath of the 2017 UK General Election, some claimed that Labour performed unexpectedly well because of a surge in youth turnout. Polling estimates for the size of this ‘youthquake’ ranged from 12 to 21 points amongst 18–24 year olds. Using conventional and Bayesian statistical methods, we analyse British Election Study and British Social Attitudes random probability surveys and find no evidence of a shift in the relationship between age and turnout of this scale. Using the pooled BES and BSA reported turnout data with an informative prior that there was a modest increase in 18–24 turnout (N{6, 3}), our 95% credible interval for that change is between 0.9 and 8.8 points. Even with a strong youthquake prior (N{15.5, 3.5}), our data suggest that there is only a 4% probability that the change in turnout amongst 18–24 years olds was 12 points or higher.