Mechanism Experiments and Policy Evaluations

This paper is forthcoming in the Journal of Economic Perspectives as part of a symposium on field experiments. For excellent research assistance we thank Laura Brinkman and Michael Reddy. We thank Nava Ashraf, David Autor, Iwan Barankay, Jon Baron, Howard Bloom, Lorenzo Casaburi, Philip Cook, Stefano DellaVigna, John DiNardo, Elbert Huang, Chad Jones, Lawrence Katz, Supreet Kaur, John List, Stephan Meier, David Moore, Steve Pischke, Harold Pollack, Dina Pomeranz, David Reiley, Frank Schilbach, Robert Solow, Tim Taylor and conference participants at the University of Pennsylvania's Wharton School of Business and the American Economic Association for helpful comments. For financial support we thank the Russell Sage Foundation (through a visiting scholar award to Ludwig). Any errors and all opinions are our own. The views expressed here are those of the authors, and should not be interpreted as those of the Congressional Budget Office or National Bureau of Economic Research.