The array of bilateral exchange rates between the dollar and foreign currencies appears to be particularly important to the current account balance, although, of course, exchange rates, like all other prices, are determined interactively and simultaneously. As I note later, to the extent that an economy harbors elements of inflexibility, so that prices and quantities are slow to respond to new developments, the process of current account adjustment, besides affecting prices of goods and financial assets, is also more likely to adversely affect the levels of output and employment as well.
The rise of the U.S. current account deficit over the past decade appears to have coincided with a pronounced new phase of globalization that is characterized by a major acceleration in U.S. productivity growth and the decline in what economists call home bias. In brief, home bias is the parochial tendency of persons, though faced with comparable or superior foreign opportunities, to invest domestic savings in the home country. The decline in home bias is reflected in savers increasingly reaching across national borders to invest in foreign assets. The rise in U.S. productivity growth attracted much of those savings toward investments in the United States. The greater rates of productivity growth in the United States, compared with still-subdued rates abroad, have apparently engendered corresponding differences in risk-adjusted expected rates of return and hence in the demand for U.S.-based assets.
Home bias implies that lower risk compensation is required for geographically proximate investment opportunities; when investors are familiar with the environment, they perceive less risk than they do for objectively comparable investment opportunities in far distant, less familiar environments.
Home bias was very much in evidence for a half century following World War II. Domestic saving was directed predominantly toward domestic investment. Because the difference between a nations domestic saving and domestic investment is the near-algebraic equivalent of that nations current account balance, external imbalances were small.1
However, starting in the 1990s, home bias began to decline discernibly, the consequence of a dismantling of restrictions on capital flows and the advance of information and communication technologies that has effectively shrunk the time and distance that separate markets around the world. The vast improvements in these technologies have broadened investors vision to the point that foreign investment appears less risky than it did in earlier times.
Accordingly, the weighted correlation between national saving rates and domestic investment rates for countries representing four-fifths of world gross domestic product (GDP) declined from a coefficient of around 0.97 in 1992, where it had hovered since 1970, to an estimated low of 0.68 last year.2
To be sure, international trade has been expanding as a share of world GDP since the end of World War II. Yet, through the mid-1990s, the expansion was largely a grossing up of individual countries exports and imports. Only in the past decade has expanding trade been associated with the emergence of ever-larger U.S. trade and current account deficits, matched by a corresponding widening of the aggregate external surpluses of many of our trading partners, most recently including China and the OPEC countries.
Indeed, the increasing dispersion of current account balances is closely tied to the shrinking degree of correlation of country shares of saving and investment.3 Obviously, if domestic saving exactly equaled domestic investment for every country, all current accounts would be in balance, and the dispersion of such balances would be zero. Thus, current account imbalances require the correlation between domestic saving and investment--which reflects the ex post degree of home bias--to be less than 1.0.
Home bias, of course, is only one of several factors that determine how much a nation actually saves and what part of that saving, or of foreign saving, is attracted to fund domestic investment. Aside from the ex ante average inclination of global investors toward home bias, the difference between domestic saving and domestic investment--that is, the current account balance--is determined by the anticipated rate of return on foreign investments relative to domestic investments as well as the underlying propensity to save of one nation relative to that of other nations.
Indeed, all these factors working simultaneously determine the extent to which domestic savers reach beyond their borders to, on net, invest in foreign assets and thereby facilitate current account surpluses and the financing of other countries current account deficits.
（ Federal Reserve，AlanGreenspan）
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