Thanks to Ran Abramitzky, to Hao Dong, our scheduled discussant, and to members of the seminar audience at the University of Hong Kong for comments. Thanks as well to Ted Telford who provided parts of the data. Financial support from NIH under grant NICHD Award HD042731-01 is gratefully acknowledged. 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 They have not been peer-reviewed or been subject to the review by the NBER Board of Directors that accompanies official NBER publications.