And so it happened that Holman and colleagues from the University of California, Irvine, found themselves in the midst of a national crisis, sitting on data about the mental wellbeing of nearly 5,000 people just before it happened. They decided to find out if that had changed in the weeks afterwards.

It’s intuitively obvious that being physically present for – or personally affected by – a terrorist incident is likely to be bad for your mental health. By chance, there were some people in the study who had first-hand experience of the bombings, and it was indeed true that their mental health suffered. But there was also a twist.

Another group had been even more badly shaken: those who had not seen the explosion in person, but had consumed six or more hours of news coverage per day in the week afterwards. Bizarrely, knowing someone who had been injured or died, or having been in the vicinity as the bombs went off, were not as predictive of high acute stress.

“It was a big ‘aha’ moment for us,” says Holman. “I think people really strongly, deeply underestimate the impact the news can have.”