@techreport{NBERw14706,
 title = "Comparing IV With Structural Models: What Simple IV Can and Cannot Identify",
 author = "James J. Heckman and Sergio Urzua",
 institution = "National Bureau of Economic Research",
 type = "Working Paper",
 series = "Working Paper Series",
 number = "14706",
 year = "2009",
 month = "February",
 URL = "http://www.nber.org/papers/w14706",
 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.},
}