美国经济离萧条有多远？ Robert J. Barro

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Robert J. Barro

这些天的中心话题是：美国的经济衰退会有多严重，会持续多久？

最严重的忧虑是，这次衰退会比1982年那次美国二战后最大规模的经济衰退更为严重，当时美国实际人均国内生产总值(GDP)下滑了3%，失业率最高时达到了近11%。那么我们这次是否会经历一次萧条？人均GDP或消费下降达到10%即构成经济萧条。

美国宏观经济在如此长的时间内一直表现如此平稳，以致于单看美国经济数据，根本得不出有关萧条概率的准确情况。我在研究中查阅了许多国家的长期数据，考虑了萧条和股市崩盘之间的历史联系。（我和约瑟•乌苏亚(Jose Ursua)上个月为美国国家经济研究局(NBER)撰写了一篇名为《股市崩盘与萧条》(Stock-Market Crashes and Depressions)的研究报告，其中阐述了这一研究。）

David Gothard 基本结论是，美国有充足的理由担忧陷入经济萧条。美国GDP和消费跌幅达到10%的可能性大概有五分之一，这是上世纪三十年代初以来所未见的。

我们发现，1870年之后美国经济只有两次可谓陷入了萧条：1929年-1933年的大萧条时期，宏观经济下滑25%；1917年-1921年的一战后时期，当时经济总量下滑了16%。我们还收集了33个其他国家的GDP、消费和股市回报等长期数据，时期最远可上溯到1870年。我们的猜想是，萧条可能和股市崩盘有着密切关联（至少我们认为股市崩盘预示着出现萧条的概率显著上升）。

这个观点似乎和萨缪尔森(Paul Samuelson)1966年那句经常被人提及的讽刺性妙语存在冲突，他当时说，“过去出现了五次经济衰退，股市却预测到了九次”。话说的很聪明，但却不公平地贬低了股市的预测能力。实际上，发生股市崩盘显著提高了萧条出现的几率。与此相反，没有出现股市崩盘则降低了萧条出现的可能性。

我们的数据涉及了251次股市崩盘（即股市的累积实际回报率低于-25%）以及97次经济萧条。股市崩盘和经济萧条的时间发生吻合的有71次。例如，美国股市在1929-31年间下跌了55%，而宏观经济在1929-33年间下滑了25%。类似的，芬兰在1989-91年间股市下滑了47%，而宏观经济在1989-93年间下滑了13%。我们发现，有30次与股市崩盘和经济萧条同时出现的还有战争。实际上，二战是那段时期最糟糕的宏观经济事件，只有美国经济在战时一枝独秀地实现了强劲增长。

在二战后这段时期，经济合作与发展组织(OECD)成员国在2008年之前都令人瞩目地保持了经济平稳。这段时间最严重的宏观经济事件出现在九十年代初的芬兰。瑞典也在上世纪九十年代初面临过一场金融危机，不过政府反应迅速，如今还被视为引导美国经济走出当前危机的可能样板。

再将目光投向经合组织以外，二战后股市崩盘和经济萧条相互关联的情况出现了很多次──包括上世纪八十年代的拉美债务危机、九十年代中期墨西哥金融危机、九十年代末的亚洲金融危机以及持续到2002年的阿根廷金融动荡。

通过研究34个国家的所有历史事件，我们发现股市崩盘后出现“轻度萧条”（宏观经济下滑10%以上）的概率为28%。股市崩盘后出现“严重萧条”（经济下滑25%以上）的可能性为9%。反过来，“轻度萧条”伴随着股市崩盘出现的几率为73%；而“严重萧条”几乎肯定会与股市崩盘相伴发生（我们的数据显示这一概率为92%）。

在借鉴上述研究结果时，我们应该考虑到美国和大多数其他国家目前并没有介入大规模战争（伊拉克战争和阿富汗战争不能和一战或二战相提并论）。因此，我们参考了历史上非战争时期的情况以更好地预测当前的状况──研究涉及了209次股市崩盘和59次萧条，其中有41次两者时间吻合。在这个范围内，股市崩盘和轻度萧条同时出现的可能性为20%，而股市崩盘与严重萧条同时出现的概率只有2%。不过，萧条仍然非常有可能导致股市崩盘出现──轻度萧条导致股市崩盘的概率为69%，严重萧条为83%。

最后，我们得出两个结论。没有出现股市崩盘的时期很安全，因为这时基本不可能出现经济萧条。然而，像2008-09年美国这样出现股市崩盘的情况就有严重风险。目前的经济衰退演化为经济萧条（宏观经济下滑超过10%）的可能性大约为五分之一。

不过，20%的萧条可能性也意味着有80%的几率可以避免萧条。美国曾在2000-02年（股市下挫42%）以及1973-74年（股市下挫49%）出现过股市崩盘，但这两次经济都只经历了温和衰退。因此，如果我们运气好的话，目前的经济下滑也可能是温和的，只不过可能会比二战后美国的历次衰退更为严重，包括1982年那次。

按照这种相对有利的假定，我们可能会沿着美国联邦储备委员会(Fed)主席贝南克(Ben Bernanke)近期勾勒出的道路前行，即经济会在2010年前实现复苏。另一方面，我们研究范围内的59次非战时经济萧条平均持续时间为近四年，如果我们真的出现萧条，这意味着经济在2012年之前难以明显复苏。

考虑到我们的情况，如果激进的政府政策能够降低萧条的可能性和可能规模的话，那么就应该予以考虑。不过，许多政府举措──包括罗斯福总统在大萧条时期实施的几项措施──都会令情况更糟。

我希望自己能对美国已经实施的诸多政策抱有信心，相信那些可能即将推行的政策能发挥作用。但我觉得更可能的情况是，美国经济的最终复苏与这些政策无关。

（本文作者是哈佛大学经济学教授，同时也是斯坦福大学胡佛研究所(Hoover Institution)的研究人员。）

[此贴子已经被作者于2009-3-19 14:04:26编辑过]

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关键词：Robert Rober 美国经济 robe bar Robert 萧条 Barro 美国经济

Robert J. Barro

Central questions these days are how severe will the U.S. economic downturn be and how long will it last?

The most serious concern is that the downturn will become something worse than the largest recession of the post-World War II period -- 1982, when real per capita GDP fell by 3% and the unemployment rate peaked at nearly 11%. Could we even experience a depression (defined as a decline in per-person GDP or consumption by 10% or more)?

The U.S. macroeconomy has been so tame for so long that it's impossible to get an accurate reading about depression odds just from the U.S. data. My approach uses long-term data for many countries and takes into account the historical linkages between depressions and stock-market crashes. (The research is described in 'Stock-Market Crashes and Depressions,' a working paper Jose Ursua and I wrote for the National Bureau of Economic Research last month.)

The bottom line is that there is ample reason to worry about slipping into a depression. There is a roughly one-in-five chance that U.S. GDP and consumption will fall by 10% or more, something not seen since the early 1930s.

Our research classifies just two such U.S. events since 1870: the Great Depression from 1929 to 1933, with a macroeconomic decline by 25%, and the post-World War I years from 1917 to 1921, with a fall by 16%. We also assembled long-term data on GDP, consumption and stock-market returns for 33 other countries, sometimes going back as far as 1870. Our conjecture was that depressions would be closely connected to stock-market crashes (at least in the sense that a crash would signal a substantially increased chance of a depression).

This idea seems to conflict with the oft-repeated 1966 quip from Paul Samuelson that 'The stock market has predicted nine of the last five recessions.' The line is clever, but it unfairly denigrates the predictive power of stock markets. In fact, knowing that a stock-market crash has occurred sharply raises the odds of depression. And, in reverse, knowing that there is no stock-market crash makes a depression less likely.

Our data reveal 251 stock-market crashes (defined as cumulative real returns of -25% or less) and 97 depressions. In 71 cases, the timing of a market crash matched up to a depression. For example, the U.S. had a stock-market crash of 55% between 1929-31 and a macroeconomic decline of 25% for 1929-33. Likewise, Finland had a stock-market crash of 47% for 1989-91 and a macroeconomic fall of 13% for 1989-93. We found that 30 cases where there were both crashes and depressions were also associated with wars. In fact, World War II is the worst macroeconomic event of the period, with strong U.S. wartime economic growth as an outlier.

In the post-World War II period, the Organisation for Economic Co-operation and Development (OECD) countries were strikingly tranquil up to 2008. The worst macroeconomic event in that period came in Finland in the early 1990s. Sweden also faced a financial crisis in the early 1990s, though it reacted quickly and is now being touted as a possible guide for leading the U.S. out of its current economic crisis.

Outside of the OECD, there have been many linked stock-market crashes and depressions since World War II -- including the Latin American debt crisis of the 1980s, Mexico's financial crisis in the mid-1990s, the Asian financial crisis of the late 1990s, and Argentina's financial turbulence that lasted until 2002.

Looking at all of the events from our 34-country history, we find that there is a 28% probability that a 'minor depression' (macroeconomic decline of 10% or more) will occur when there is a stock-market crash. There is a 9% chance that a 'major depression' (a fall of 25% or more) will occur when there is a stock-market crash. In reverse, the chance that a minor depression will also feature a stock-market crash is 73%. And major depressions are almost sure to have stock-market crashes (our data show the probability is 92%).

In applying our results to the current environment, we should consider that the U.S. and most other countries are not involved in a major war (the Iraq and Afghanistan conflicts are not comparable to World War I or World War II). Thus, we get better information about today's prospects by consulting the history of nonwar events -- for which our sample contains 209 stock-market crashes and 59 depressions, with 41 matched by timing. In this context, the probability of a minor depression, contingent on seeing a stock-market crash, is 20%, and the corresponding chance of a major depression is only 2%. However, it is still the case that depressions are very likely to feature stock-market crashes -- 69% for minor depressions and 83% for major ones.

In the end, we learned two things. Periods without stock-market crashes are very safe, in the sense that depressions are extremely unlikely. However, periods experiencing stock-market crashes, such as 2008-09 in the U.S., represent a serious threat. The odds are roughly one-in-five that the current recession will snowball into the macroeconomic decline of 10% or more that is the hallmark of a depression.

The bright side of a 20% depression probability is the 80% chance of avoiding a depression. The U.S. had stock-market crashes in 2000-02 (by 42%) and 1973-74 (49%) and, in each case, experienced only mild recessions. Hence, if we are lucky, the current downturn will also be moderate, though likely worse than the other U.S. post-World War II recessions, including 1982.

In this relatively favorable scenario, we may follow the path recently sketched by Federal Reserve Chairman Ben Bernanke, with the economy recovering by 2010. On the other hand, the 59 nonwar depressions in our sample have an average duration of nearly four years, which, if we have one here, means that it is likely recovery would not be substantial until 2012.

Given our situation, it is right that radical government policies should be considered if they promise to lower the probability and likely size of a depression. However, many governmental actions -- including several pursued by Franklin Roosevelt during the Great Depression -- can make things worse.

I wish I could be confident that the array of U.S. policies already in place and those likely forthcoming will be helpful. But I think it more likely that the economy will eventually recover despite these policies, rather than because of them.


(Mr. Barro is a professor of economics at Harvard and a fellow at Stanford University's Hoover Institution.)

顶，

翻译的不错

不过，有点仓促的痕迹

我看就是找了些数据算了个概率题

股市的衰退应该和经济大萧条有联系吧。股市代表的是投资市场当投资锐减时，会产生的恶劣的影响是不可估量的。从整个逻辑的角度将应该是这样的吧

股市是反映未來的情況,所以不是因蕭條後大跌而是看壞未來才大跌.

萧条谁能预测？神仙都没招。从历史看只能给我们参考，但除了这个，我们还能指望什么呢

谁都说不准将来的形势啊，静观其变~~

家无永富啊

巴罗，顶一下