, the Editor, two anonymous referees, and seminar participants at Bocconi, Harvard, MIT, the NBER Summer Institute and the 2012 ASSA Meeting. The views expressed herein are those of the authors and do not necessarily reflect the views of the National Bureau of Economic Research. NBER working papers are circulated for discussion and comment purposes. They have not been peerreviewed or been subject to the review by the NBER Board of Directors that accompanies official NBER publications.