---- Acknowledgements -----
We thank Stephanie Aaronson and Daron Acemoglu for comments on earlier versions of this paper. Kristin Mayer and Benjamin Pugsley provided excellent research assistance. The views expressed in this paper are those of the authors and do not necessarily reflect the views of the Federal Reserve Bank of New York or the Federal Reserve System. This research was supported by the U.S. Social Security Administration through grant #10-P98363-1-04 to the National Bureau of Economic Research as part of the SSA Retirement Research Consortium. The findings and conclusions expressed are solely those of the authors and do not represent the views of SSA, any agency of the Federal Government, or the NBER.