Today, Iceland tops the European table for the cleanest-living teens. The percentage of 15- and 16-year-olds who had been drunk in the previous month plummeted from 42 per cent in 1998 to 5 per cent in 2016. The percentage who have ever used cannabis is down from 17 per cent to 7 per cent. Those smoking cigarettes every day fell from 23 per cent to just 3 per cent.
The way the country has achieved this turnaround has been both radical and evidence-based, but it has relied a lot on what might be termed enforced common sense. “This is the most remarkably intense and profound study of stress in the lives of teenagers that I have ever seen,” says Milkman. “I’m just so impressed by how well it is working.”