RANDOMISED controlled trials form the basis of modern medicine for good reason: they are the only trustworthy way we have for evaluating interventions. Their usefulness is not limited to medicine, however. They can be designed to test the effectiveness of many kinds of policy, from education to crime.
Such trials often reveal that policies do not work, or worse. School-based driving lessons, for instance, have increased the number of car accidents (see “Let science rule: the rational way to run societies”). As the saying goes, the road to hell is paved with good intentions.
So why aren’t rigorous trials…
