The abstract is this:
Randomized experiments have become a popular tool in development economics research, and have been the subject of a number of criticisms. This paper reviews the recent literature, and discusses the strengths and limitations of this approach in theory and in practice. We argue that the main virtue of randomized experiments is that, due to the close collaboration between researchers and implementers, they allow the estimation of parameters that it would not otherwise be possible to evaluate. We discuss the concerns that have been raised regarding experiments, and generally conclude that while they are real, they are often not specific to experiments. We conclude by discussing the relationship between theory and experiments.