Yale University is perhaps the epicentre of the campus activism so voguish today. Two professors stepped down from pastoral roles last year after a controversy about whether students should police their own offensive Halloween costumes, rather than letting the university do it for them, provoking protests from hundreds of students. Yale is also debating whether to discontinue using the word “freshman” in favour of the more gender-neutral term “first-year”.

That Yale is also one of America’s most prestigious universities is not coincidental. Across the country, colleges with richer, high-achieving students are likelier to witness protests calling for controversial speakers to be disinvited. Recent flare-ups at Middlebury College, which tried to prevent Charles Murray, a conservative writer, from speaking and left the professor interviewing him with a concussion, and at the University of California, Berkeley which had to cancel a speech by Milo Yiannopoulos, an over-exposed provocateur, are but the tip of a larger pile.

Following the work of Richard Reeves and Dimitrios Halikias of the Brookings Institution, The Economist analysed data on student attempts to disinvite speakers since 2013 collected by the Foundation for Individual Rights in Education, an advocacy group. Even among selective universities, those with better-credentialed and wealthier students are likelier to mount protests. They are also likelier to mount successful attempts to block speakers.

This could be because elite students attract controversial speakers more often. Reeves, who is also a biographer of John Stuart Mill, reasons otherwise. America’s best universities contain bubbles in which “certain left-of-centre tenets, largely around identity politics, take on the weight of an orthodoxy”, he says. Mill, who wrote that squashing freedom of expression results in “a kind of intellectual pacification” that sacrifices “the entire moral courage of the human mind,” wouldn’t have liked it very much.