In a recent randomized experiment we found mean returns to capital of between 5 and 6 percent per month in Sri Lankan microenterprises, much higher than market interest rates. But returns were found to be much higher among men than among women, and indeed were not different from zero for women....

"Randomized experiments are increasingly used in development economics, with researchers now facing the question of not just whether to randomize, but how to do so. Pure random assignment guarantees that the treatment and control groups will have identical characteristics on average, but in any...