@TechReport{iza:izadps:dp3980,
            	author={Heckman, James J. and Urzua, Sergio},
            	title={Comparing IV with Structural Models: What Simple IV Can and Cannot Identify},
            	year={2009},
	month={Jan},
            	institution={Institute of Labor Economics (IZA)},
            	address={Bonn},
            	type={IZA Discussion Paper},
            	number={3980},
            	url={https://www.iza.org/publications/dp3980},
	abstract={This paper compares the economic questions addressed by instrumental variables estimators with those addressed by structural approaches. We discuss Marschak's Maxim: estimators should be selected on the basis of their ability to answer well-posed economic problems with minimal assumptions. A key identifying assumption that allows structural methods to be more informative than IV can be tested with data and does not have to be imposed.},
	keywords={Marschak's Maxim;instrumental variables;structural approaches},
            }