This paper from the Institutional Learning and Change (ILAC) Initiative provides a range of technical and practical reflections on the use of randomised control trials in impact evaluation.
"It is divided into three parts. The first part discusses RCTs in impact evaluation, their origin, how they have developed and the debate that has been generated in the evaluation circles. The second part examines difficult issues faced in applying RCT designs to the impact evaluation of development initiatives, to what extent this type of design can be applied rigorously, the validity of the assumptions underlying RCT designs in this context, and the opportunities and constraints inherent in their adoption. The third part discusses the some of the ethical issues raised by RCTs, the need to establish ethical standards for studies about development options and the need for an open mind in the selection of research options and tools." (Barahona, 2010)
Barahona, C. Institutional Learning and Change (ILAC), (2010). Randomised control trials for the impact evaluation of development initiatives: A statistician’s point of view.