Introduction: Randomization in the Tropics Revisited, a Theme and Eleven Variations

Development economists have been using randomized controlled trials (RCTs) for the best part of two decades,1 and economists working on welfare policies in the US have been doing so for much longer. The years of experience have made the discussions richer and more nuanced, and both proponents and critics have learned from one another, at least to an extent. As is often the case, researchers seem reluctant to learn from earlier mistakes by others, and the lessons from the first wave of experiments, many of which were laid out by Jim Heckman and his collaborators...