When Fazle Hasan Abed set out to lower death rates among poor children in rural Bangladesh, by teaching mothers how to treat dehydration, he was careful not to pay his field workers per household reached, but on how well their subjects, often illiterate or semi-literate mothers, could answer questions afterwards.

His approach, to reward high-quality instruction and rigorously monitor results of a door-to-door pilot scheme in the 1980s, fed lessons from the field back to research labs in Dhaka, and has been credited with saving countless lives from being lost to diarrhoea, a major source of child mortality in the country. It also propelled Brac, which Abed founded in 1972 as the Bangladesh Rehabilitation Assistance Committee to help refugees returning to their homeland after the liberation war of 1971, to become one of the largest non-profit development organisations in the world.