Let us take out of the Hospitals, out of the Camps, or from elsewhere, 200, or 500 poor People, that have Fevers, Pleurisies, etc... Let us divide them in Halfes, let us cast lots, that one half of them may fall to my share and the other to yours; I will cure them without bloodletting and sensible evacuation; but do you do as ye know (for neither do I tye you up to the boasting, or of Phlebotomy, or the abstinence from a solutive Medicine) we shall see how many Funerals both of us shall have: But let the reward of the contention or wager, be 300 Florens, deposited on both sides: Here your business is decided.
That was Jean Baptiste van Helmont in the 17th century. It took three hundred years for randomized trials to become widespread in the medical profession. Now the MIT Poverty Action Lab, among others, is advocating their use in evaluating the effectiveness of development projects (and other policy interventions). Since many projects are rolled out gradually, rolling them out with some randomization generates very good data without much extra effort required.