old man: Yet each is free to live as he chooses. Though they seem opposite, both are true.
Kung Fu, Pilot
Our path begins with experimental random assignment, both as a framework for causal
questions and a benchmark by which the results from other methods are judged. We illustrate the awesome power of random assignment through two randomized evaluations of the effects of health insurance. The appendix to this chapter also uses the experimental framework to review the concepts and methods of statistical inference.