Should economics be more like medicine? I don’t mean that economists should be more like doctors – I’ve met a few doctors – but that economists should learn from the relationship that medical practice has with medical evidence.

Medicine, like economics, deals with complex systems that are still not well understood; like economics, it has its share of quacks; but unlike economics, medicine has swallowed many of its ethical qualms about running controlled experiments in difficult circumstances.

Randomised controlled trials are now catching on in economics, especially development economics. (Such a trial would involve, for instance, approving loans to a randomly chosen subset of loan applicants.) Two new books, Poor Economics and More Than Good Intentions, each by leading practitioners of randomised trials, explain the consequent discoveries.