Unlike previous researchers, the authors were able to track all the children and account for their parental background and cognitive ability. They found that the 13-year-olds who wanted the smaller sum of money at once were 32% more likely to be convicted of a crime during the next 18 years than those children who said they would rather wait for the bigger reward. Individuals who are impatient, they believe, prefer instant benefits and are therefore less likely to be deterred by potential punishments.

But those who fret that a person’s criminal path is set already as a teenager should not despair. The four researchers offer a remedy. When the respondents'education was included in the analysis, they found that higher educational attainment was linked to a preference for delayed gratification. “We therefore suspect that schooling can deter people from crime by making them value the future more,” explains Mr Gronqvist.

Educational attainment and patience are related either because patience helps students to do better or because schooling makes people more likely to postpone rewards. Fortunately, there is evidence in support of the latter theory. Francisco Perez-Arce of the RAND Corporation, a think-tank, interviewed around 2,000 applicants for Mexican universities. The students had similar credentials but some obtained admission through a lottery to a university that did not charge tuition fees, whereas the rest had to apply elsewhere. As a result, a higher proportion of lottery-winners than losers went to college. After a year, Mr Perez-Arce found, the lottery-winners were more patient than the losers. Since the process was random, he concluded that higher education can make people place more weight on the future.

Victor Hugo supposedly said, “He who opens a school door closes a prison.” Homer is not the only great writer with lessons for economic research.