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...

Education in Denmark is freely available. Despite near equal teacher salaries and per-pupil school expenditure across districts, there is substantial spatial heterogeneity in school quality as measured by teacher quality and student test scores. We argue that this is due to sorting of teachers...