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格林斯潘论國际失衡
格林斯潘论國际失衡[摘要] 美國经常帐户赤字在过去十年的增加过程，看起来伴随着一次明显的全球化新阶段，其特征是，美國的生产率出现了大幅度加速速度，而经济学家所说的本國偏见（home
bias）则在下降。
（海外论坛·北京）2003年11月，我曾指出，我看不出什么有力的证据表明，有什么东西能够减少为美國的经常帐户赤字，即使自2002年初以后，美國的实际汇率已经净下跌了10%。通货膨胀和包含在长期利率中的通货膨胀贴水－－这是一種货币疲软的典型症状－－似乎被曳N屏耍罅繃蚀⑿盍魅朊绹涑擅绹耐蹲剩床⒚挥卸試式鹑谑谐〈聪拗频娜怕摇Ａ侥旰螅榭霾⒚挥卸啻蟊浠皇俏颐堑木Ｕ驶С嘧指罅恕４蠖嗍咧贫ㄕ叨级悦绹绦С制渚Ｕ驶С嘧帜欠N表面上的轻松有点惊奇。
当然，赤字会累积成为不断增长的对外净债务，会导致维持成本的 不断上升，因而它不可能无限地持续下去。看到美國人的债务越来越多，外國投资者终有一天会退缩的，即使在美國的投资回报率依然相对较高，他们将会改变自己的投资组合。除此之外，美國人解决其國内失衡的努力，推测起来，也有助于其摆脱经常帐户失衡。
不管怎样，经常帐户恢复某種平衡需要一个范围广泛的互动过程，涉及到商品、服务和收入在一个國家的居民与世界其他國家的居民之间的生产和分配。这一过程的结果则完全取决于國内与國际的产品和资产价格，包括利率。
美國与外國货币之间的双边汇率格局对于经常帐户平衡似乎尤其重要，尽管汇率同时也受其他价格的影响。我后面将会指出，一个经济体如果包含着刚性因素，这些价格和数量对新变化的反应就会比较缓慢，经常帐户调整的过程，除了影响商品和金融资产价格之外，也更有可能对产出和就业水平产生负面影响。
美國经常帐户赤字在过去十年的增加过程，看起来伴随着一次明显的全球化新阶段，其特征是，美國的生产率出现了大幅度加速速度，而经济学家所说的本國偏见（home
bias）则在下降。简而言之，本國偏见就是一个人尽管面对着國外的比较优势或绝对优势，却依然在本國投资國内储蓄的狭隘倾向。本國偏见的下降表明，储蓄人越来越多地跨越國界投资于外國资产。美國生产率的提高吸引大量此类储蓄投资于美國。美國相对于外國较高的生产率增长速度显然造成了在经过风险调整的预期回报率、因而是在对美國资产的需求方面的差异。
本國偏见意味着，地理上更临近的投资机会只需要较低的风险补偿；投资者熟悉该环境，在他们眼里风险就比投资于遥远的、自己不熟悉的地方更小，即使客观地说，那里具有比较投资机会（comparable
investment opportunities）。
在第二次世界大战后的半个世纪中，有大量本國偏见的证据。國民储蓄天然地转换为國内投资。由于一國的國内储蓄和國内投资之间的差大体上就等于该國的经常帐户盈余，因而，外部失衡是较小的。
但是，自90年代开始，本國偏见开始明显下降，这是解除资本流动限制及信息通信技术发展的结果，后者有效地缩短了把全世界各个市场分开的时间与距离。这些技术领域的巨大改进要拓宽了投资者的视野，他们认识到，到外國投资的风险比以前要小了。
因而，在占有世界GDP总额的五贩N膰抑校瑖翊⑿盥视雵谕蹲事手涞募尤ㄏ喙匦韵凳�1992年的0.97－－自1970年以来一直在这个水平徘徊－－下降到去年的0.68（估计数）。
自第二次世界大战以来，國际贸易占GDP的比例也确实在上升。但是，在90年代中期，这種上升主要是各个國家的进出口增长的结果。只是在过去十年，不断增长的贸易才伴随着美國越来越大的贸易和经常帐户赤追N鱿郑氪送保颐堑暮芏嗝骋谆锇榈亩酝庥嘧芏钤诓欢侠┐螅罱绕浒ㄖ袊蚈PEC國家。
经常帐户盈余越来越大的离散度，与國内储蓄和投资比例之相关程度的缩减有密切关系。显然，假如每个國家的國内储蓄正好等于國内投资，所有的经常帐户都处于平衡中，这種盈余的离散度就是零。因而，经常帐户盈余要求國内储蓄与投资之间的相关性－－它反映的是事后可以分析出来的本國偏见的水平－－小于1。
当然，本國偏见只是决定一个國家实际储蓄了多少、该储蓄或外國储蓄的多大部分被吸引变成國内投资的几个因素中的一个。除了全球投资者事前的平均本國偏见倾向之外，國内储蓄与國内投资间恩人差－－也即经常帐户盈余－－是由对外投资相对國内投资的预期回报率所决定的，也是由一國相对于它國的储蓄倾向决定的。
事实上，所有这些因素同时决定着國内储蓄者走出他们的边界、净投资于外國资产、从而增加经常帐户盈余、为其他國家的经常帐户赤字提供资金的幅度。
原文：Remarks by Chairman Alan Greenspan
International imbalances
In November 2003, I noted that we saw little evidence of stress in funding
the U.S. current account deficit even though the real exchange rate for the
dollar, on net, had declined more than 10 percent since early 2002. Inflation
and inflation premiums embedded in long-term interest rates--the typical symptoms
of a weak currency--appeared subdued, and the vast international savings transfer
to finance U.S. investment had occurred without measurable disruption to international
financial markets. Two years later, little has changed except that our current
account deficit has grown still larger. Most policy makers marvel at the seeming
ease with which the United States continues to finance its current account deficit.
Of course, deficits that cumulate to ever-increasing net external debt, with
its attendant rise in servicing costs, cannot persist indefinitely. At some
point, foreign investors will balk at a growing concentration of claims against
U.S. residents, even if rates of return on investment in the United States remain
competitively high, and will begin to alter their portfolios. In addition, efforts
by U.S. residents to address their domestic imbalances will presumably contribute
to a move away from current account imbalance.
In all instances, a current account balance essentially results from a wide-ranging
interactive process that involves the production and allocation of goods, services,
and incomes among the residents of a country and those of the rest of the world.
The outcome of the process is reflected in the full array of domestic and international
product and asset prices, including interest rates.
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 nation's domestic saving and domestic investment is
the near-algebraic equivalent of that nation's 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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