6  The R² of a simple regression using quarterly data since 1952 is 0.5. Adding a trend to reflect the influence of other factors such as the greater income elasticity of demand of U.S. imports relative to that of exports raises the R² to 0.7 and does not reduce the significance of the connection between home mortgage debt and the current account.
7  To be sure, the rapid globalization of the latter part of the nineteenth century exhibited many of the characteristics of today's international economy. But the far lower level of technology and the existence of the gold standard adjustment process renders that period of little use for current comparisons.