---- Acknowledgements ----
We thank the exceptional research assistance of Deirdre Daly. We have benefitted from the comments of Chang-Tai Hsieh, discussions with Fernando Alvarez and Lars Hansen, and feedback from participants in seminars at the University of British Columbia, Queen's University, and the Federal Reserve Bank of Chicago. A condensed version of this paper is forthcoming in the American Economic Review: Papers and Proceedings. Eaton and Kortum gratefully acknowledge the support of the National Science Foundation. Any opinions expressed are those of the authors and not necessarily those of the Federal
Reserve System, the NBER, or the NSF.