What’s the best way of persuading parents in developing countries to immunize their kids? Do women politicians make a difference to what policies are pursued? If you want to reduce malaria is it best to give people mosquito nets for free or make them pay? The influential economist Esther Duflo has revolutionised the way we answer these questions. The secret is to introduce RCTs - Randomized Control Trials. Producer: Dave Edmonds (Image: Nurse with Needle, Credit: Shutterstock)