NBER Working Paper No. 15349
---- Acknowledgements ----
We thank Satyajit Chatterjee, Elhanan Helpman, Robert Helsley, Gianmarco Ottaviano, Diego Puga, Steve Redding and various seminar participants for useful comments. Financial support from the Sloan Foundation, the European Commission (EFIGE 225343), the Comunidad de Madrid (PROCIUDAD-CM), and the Spanish Ministry of Science (ECO2008-01300) is gratefully acknowledged. The views expressed herein are those of the author(s) and do not necessarily reflect the views of the National Bureau of Economic Research.