4  Laurence Ball, Douglas W. Elmendorf, and N. Gregory Mankiw, “The Deficit Gamble,” Journal of Money, Credit, and Banking, vol. 30, no. 4, (November 1998), pp. 699-720, show that interest rates on domestic government debt have generally been slightly less than the GDP growth rate in past decades.
5  The rate-of-return puzzle is in turn a question about why foreign direct investment in the United States has such a low rate of return. See Raymond J. Mataloni, Jr., “An Examination of the Low Rates of Return of Foreign-Owned U.S. Companies,” Survey of Current Business, vol. 80 (March 2000), pp. 55-73.