In Search of the Armington Elasticity, joint with Philip Luck, Maurice Obstfeld and Katheryn N. Russ. NBER Working Paper No. 20063, April 2014. Published version in the Review of Economics and Statistics, March 2018.
Technology in the Great Divergence, November 2001, with Gregory Clark. NBER working paper no. 8596. Published version in the Michael D. Bordo, Alan M. Taylor, and Jeffrey G. Williamson, eds, Globalization in Historical Perspective, Univ. of Chicago and NBER, January 2003, 277-314.