经济学家为什么要自欺欺人呢？　2009-06-10 08:26
分类：默认分类 字号： 大大 中中 小小 　[点击查看Scott Sumner的英文博客] [Scott Sumner中文博客]



这次有所不同（抑或相同）



在较早的一篇文章中我曾经说过联邦政府的政策大多反映了经济学家的一致意见。因此大部分经济学家都不能够在事发当时意识到货币政策的不足之处。我将此推测推及到通货膨胀和通货紧缩之中。如今我们能否将此推测推广的更远呢？



我想说明几乎美国每次经济萧条都有两个共同特征：



1. 紧缩银根触发NGDP（名义GDP）增速趋缓，从而导致经济衰退。



2. 每次经济衰退，大多数经济学家都会极力否认第一点适用于当前问题。



这是一个非常大胆的观点，但是你还能指望从一篇名为“货币幻觉”的博客中得到什么呢？



当经济学家回顾美国历史宏观数据的时候他们发现名义冲击和实际产量之间存在密切的联系。主流观点（我所坚信的）认为经济衰退表明了需求监控不力。货币学派总是对货币政策吹毛求疵，近几十年来，新凯恩斯学派几乎也采取了这个观点。（相比之下，后凯恩斯学派往往认为货币政策的作用是来源于内部。例如，名义货币供给可能是由商业周期所决定的。）



简单地说，当AD(社会总需求曲线)左移或者右移的速度急剧减慢时，经济萧条就出现了。这导致了NGDP增速的急剧下降。因为NGDP增速在经济萧条中会急剧下降，也因为货币政策能够并且应该试图稳定NGDP的增长，宏观经济学致力于寻找最优货币规则就一点都不奇怪了。



这里有一个问题。经济学家同意AD(社会总需求)缓慢增长会导致经济萧条，货币政策能够并且应该稳定AD(社会总需求)的增长，但是他们绝不承认当前经济萧条是由于货币政策的失误所引起的。永远都是“这次有所不同”。年轻的读者可能不了解，但是每次经济萧条都会有一批文章竭力证明“这次不同于以往的经济萧条” 。想想看，可不是吗？



【或许有人能帮我找到近期的一些详细引用了1990-1991经济萧条时期新闻媒体报道的文章，如我们所知，它是如何不同于以往经济萧条，证明资本主义终结的】



美联储反映了主流经济学家的一致意见，他们肯定不会因任何一次经济萧条而自我批判，（经济学家也是有自尊的）。同时，经济学家又意识到他们书中的理论表明了经济萧条是由货币政策的失误所导致。因此，需要有一些合理的原因来解释为什么这次不应被指责。因此，“这次有所不同”就是一个适用于所有场合的很好的借口。



经济学家为什么要这样自欺欺人呢？我认为有以下几种可能：



1.名义利率通常会在经济萧条中急剧下滑。即使是在智力层面上，经济学家更应该了解。我注意到大多数经济学家认为货币政策在紧缩银根降低NGDP增速的当时是“轻而易举的”。不仅仅是这次的经济萧条，包括可数的所有经济萧条。这个问题我已经说了很多了，接下来我要说另一个话题了。



2.经济萧条通常和实际冲击（石油、科技、房地产泡沫等）联系在一起。实际冲击要比有关货币失调的隐性问题更容易辨认。



这次经济萧条如何呢？货币学家为什么不指责紧缩银根政策呢？排除那些否认货币政策会影响名义统计的极端主义者，在两种情况下货币政策制定者会被免于问罪。



1. 经济萧条可能是由于一些实际因素所引起的。这种情况下，NGDP的增长可能会导致更大的通货膨胀。



2. 能够稳定NGDP增长的货币政策可能在政治上行不通。



Arnold Kling认为刺激手段不可能一直有效，因为我们所面临的不是类似于资源重新配置那样的“产出缺口”问题。我将之理解为任何试图通过货币政策人为刺激经济的努力只会导致通货膨胀或者是助长经济泡沫。



Paul Krugman似乎是想说明货币刺激在政治上是行不通的，因为为了让实际利率达到一个合适的水平，我们需要计算出一个不合情理的高利率期望值。前面几篇文章，我已经说过Krugman好象是在自相矛盾，因为他从传统凯恩斯主义立场出发指明SRAS(短期总供给曲线) 处于一个相对缓和的急速下跌状态，任何实际产量的恢复都需要对于政治上来说是不能被接受的通货膨胀率。我一直希望他的拥护者能够给我做出合理的解释。（我需要说明过去曾经有一些克鲁格曼的拥护者访问过我的博客）



我度假的时候读过一本宇宙学方面的书，几乎完全不知所云。作者（塔夫茨大学的一个教授，名字我忘记了）指出，宇宙起源的现行理论是“膨胀”。在书中众多让人费解的观点中（作者号称是当下的标准模型），“膨胀”理论指出实际上所有可能的宇宙都是实际存在的，因此就会有数十亿的宇宙，就像这一次，我写了相同的博客，然后有数十亿以上的博客在各方面都是相同的，除了Nick Rowe是一个后凯恩斯主义者。



[顺便说一句，道德哲学家一直因自由可能是不存在的这一想法而困惑。那么如果所有的选择都是虚构的又会怎么样呢？]



作者还指出通过预测宇宙常量至少有一个粗略的精确度，著名的“人择原理”最近获得了一些实验性的支持。我现在手头上没有这本书，但是这里有一个来自于维基百科的引述：



自然界分析的一个普遍特征是基本物理常数的期望值不能够被“过度调整”。例如，如果存在被调整的预计值（比如0），观测值不能比生命存在所要求的数值更接近于预测值。虽小但却有限的宇宙常数值可以看作是有关于此的一个成功预言。



我不会试图去解释人择原理，因为我不知道怎么说才不会使它听起来像是无谓的重复。但是那些熟悉此观点的人不妨看看以下的假设是不是与此类似。



无辜原则：关于宏观经济问题原因的一致意见倾向于使经济共同体免于遭受指责。



推论1：如果金融主管当局反映的是宏观经济学家的一致意见的话（正如在美国那样），经济学界绝不会指责是货币政策制定者导致了经济萧条。



推论2：经济学界绝不会指出本来通过适当的货币政策可能会避免的任何问题。这意味着预测统计永远不会指出经济萧条会在未来某天发生。



目前大部分有关“金融危机”的讨论集中于一个不言而喻的假设，即次贷危机导致了目前的困境。实际上，大部分学者甚至不认为有必要维护这一假设，而是费心于解释他们（还是我们？）怎么会蠢到让这样的财政混乱发生。毕竟，很明显是次贷危机导致了经济萧条，难道不是吗？



实际上并不是那么的明显。 事实上，只有次贷危机的规模足够庞大，一眼就能看出我们面临着严重的金融危机，此假设才站得住脚。但是在2007年底2008年初，人人都能看出巨大的次贷危机，大多数经济学家不但没有预测当前的经济萧条的严重性，（此次被认为是大萧条以来最严重的一次），甚至没有预测到会出现轻度衰退。所有那些满怀信心的告诉我们因何才会陷入目前的困境的经济学家们，他们甚至出版了有关于资本主义的失败的书籍，却意识不到“当前的困境”来自于大家有目共睹的原因。



我将通过引用未引起人们重视的Paul Einzig的话来得出我的结论。他看出了1937年财政当局的不称职和过分自信。（这来自于早期的文章，可能有人没看过，我不记得有人对此发表过评论）这段引用很好的概括了我关于经济学家和投资者的观点，Einzig称之为“supermen and sub-men”：



1937年6月9日， 这位学识渊博的货币专家[Cassel ]在《每日邮报》上发表了一篇让人震惊的文章，标以最深的颜色。文章指出当前形势是由于黄金过剩所引起，建议只有将黄金价格调整到将介于当前价格和过去价格之间才是唯一出路。他指出罗斯福总统的激进政策没有料到1934年1月美元会贬值41%，从而导致黄金过剩。如果我们看一下Cassel教授早期的作品，我们会发现即使是过后很长一段时间，他本人也没有料到这样的发展形势。 我们在1936年7月的季刊评论上读到Cassel教授关于Skandinaviska Kreditaktiebolaget发表了以下评论，‘好像大家普遍认为最近黄金产量激增，我们有黄金极度过剩之势。这个观点是不正确的’…… 这位博学的教授还指望区区一个政治家在1934年1月能够预测到点什么，而他本人在两年半以后都看不到问题所在。事实上，我很怀疑他是否能够预知这一问题，但是人们对于黄金过剩的恐慌，无论对错，他都看到了从前没有意识到的问题。改变了他和他的同事的观点的，既不是新发事实，也不是新科学论断的份量，而是来自于黄金储备者、投机商和其他的sub-men 的潜意识影响打开了这些supermen的视角。这些事实很大程度上降低了经济学家和经济科学在公众眼中的威望。（1937，p26-27）



经济学家是何时意识到我们正处于严重的困境之中的呢？不是在2007年底次贷危机已经露出端倪的时候，不是2008年初贝尔斯登公司险些垮掉的时候，也不是2008年夏天，工业产品和商品价格急剧下降，房地产崩溃蔓延到腹地市场的时候。直到2008年秋季当他们发现他们的401k帐户外挂，华尔街的sub-men告诉他们AD(社会总需求)在急剧下降，他们才意识到问题的严重性。



现在他们想要告诉我们错误在于贪婪的银行家或放松管制、或管制、或格林斯潘的货币政策、或油价泡沫。他们仍然不肯反思2008年底NGDP的急速下降是否反映了货币政策态势对于经济需求来说过于紧缩。估计下一代的经济学家看着极糟的NGDP数据，也不会因没有指出宏观经济学教科书建议他们应该指出的问题而感到内疚。



（翻译纠错。读者发现任何翻译错误请发邮件给我们，谢谢：caijingblog#126.com 将#改为@）




--------------------------------------------------------------------------------

英文原文（地址：http://blogsandwikis.bentley.edu/themoneyillusion/?p=1439）：

It’s (not) different this time

In an earlier post I argued that Fed policy almost always reflects the consensus views of economists, and therefore that most economists fail to perceive major monetary policy failures at the time and place they occur. I applied that conjecture to episodes of inflation and deflation. Let’s see if we can take that conjecture even further today.

I’d like to argue that almost every American recession shares two characteristics:

1. Recessions are caused by a slowdown in NGDP growth, which is triggered by tight money.

2. During every recession most economists fervently deny point 1 applies to the current problem.

That’s a pretty bold claim, but what else would you expect from a blog entitled “The Money Illusion?”

When economists look back at historical US macro data they immediately notice a strong correlation between nominal shocks and real output. The mainstream view (which is the one I adhere to) is that these recessions represent failures of demand management. Monetarists have always singled out monetary policy, and in recent decades new Keynesians pretty much adopted that view as well. (In contrast, Post-Keynesians tend to see the role of monetary policy as being endogenous, i.e. the nominal money supply might be determined by the business cycle.)

Put simply, a recession occurs whenever AD shifts to the left, or at least sharply slows the rate at which it is shifting to the right. This results in a sharp slowdown in NGDP growth. Because NGDP growth generally slows sharply in recessions, and because monetary policy can and should try to stabilize NGDP growth, it is not surprising that modern macro focuses on the search for the optimal monetary rule.

There is just one problem with this simple story. Economists do agree that slowing AD causes recession, and that monetary policy can and should stabilize AD, but they never seem to see the current recession as resulting from a failure of monetary policy. It is always “different this time.” Younger readers of this blog may not know this, but every recession produces a torrent of articles arguing that “this one is different; it’s not like past recessions.” And when you think about it, how could it be otherwise?

[Perhaps someone can help me dig up a recent article that gave scary quotations from the news media during the 1990-91 recession; how it was different from all past recessions, and represented the end of capitalism as we know it.]

The Fed reflects the consensus views of mainstream economists, and that consensus is certainly not going to blame themselves for any recession (even economists have egos.) At the same time economists are aware that the theories in their textbooks suggest that recessions are failures of monetary policy. Hence the need for some sort of excuse, some rationalization for why this time they (we) are not to blame. And the “it’s different this time” excuse is perfect—an excuse for all occasions.

How can economists delude themselves in this way? I see several possibilities.

1. Nominal interest rates generally fall sharply in recessions. Even though at an intellectual level economists should know better, I’ve noticed that most economists think money is “easy” at the very moment that tight money is reducing NGDP growth. Not just this recession, but every recession that I can recall. I’ve talked endlessly about this issue, so I’ll spare you another lecture.

2. Recessions are often associated with real shocks (oil, tech, real estate bubbles, etc) that are easier to visualize than the insidious problem of monetary disequilibrium.

What about this recession? Why don’t economists blame tight money? If we exclude the lunatic fringe who deny that monetary policy (no matter how expansionary) can impact nominal aggregates, then there are two possible ways in which monetary policymakers could be exonerated:

1. The recession may be caused by real factors. In that case an increase in NGDP may simply result in more inflation.

2. A monetary policy expansionary enough to stabilize NGDP growth may be politically infeasible.

Arnold Kling argues that stimulus may not be all that effective because what we have is not so much an “output gap” as a resource reallocation problem. I presume that means that any attempt to artificially stimulate the economy with monetary policy would merely produce inflation, or perhaps further asset bubbles.

Paul Krugman seems to argue that monetary stimulus is politically unacceptable because in order to get real interest rates to the appropriate level, we would need to generate unacceptably high expected inflation rates. In several previous posts I have argued that Krugman seems to contradict himself, as he generally argues from the traditional Keynesian position that the SRAS is relative flat in a deep slump, but then seems to suggest that any significant recovery in real output would require politically unacceptable rates of inflation. I am still waiting for one of his defenders to explain this seeming contradiction. (I might add that I have had some very articulate Krugman defenders visit my blog in the past.)

While on vacation I read a book on cosmology that I almost entirely failed to understand. The author (a Tufts Professor whose name I forget) suggested that the current theory of the origin of the universe is “inflation.” Among the many bewildering ideas in the book is his view (which he suggests is now almost the standard model) that the “inflation” theory implies that virtually all possible universes exist. Thus there are billions of universes just like this one, where I am typing out the same blog, and then billions more that are identical in every respect except that Nick Rowe is a Post Keynesian.

[BTW, moral philosophers have long been troubled by the thought that free will might not exist. What if it turned out that all possible choices are made?]

He also argued that the famous “Anthropic Principle” has recently received some experimental support, by predicting the value of the cosmological constant with at least a rough degree of accuracy. I don’t have the book with me, but here is a quotation from Wikipedia:

A generic feature of an analysis of this nature is that the expected values of the fundamental physical constants should not be “over-tuned,” i.e. if there is some perfectly tuned predicted value (e.g. zero), the observed value need be no closer to that predicted value than what is required to make life possible. The small but finite value of the cosmological constant can be regarded as a successful prediction in this sense.

I won’t try to explain the anthropic principle, as I am not sure how to do so without making it sound tautological. But for those familiar with the basic idea, consider whether the following are analogous hypotheses:

The Innocence Principle: The consensus view of the cause or causes of macroeconomic problems will tend to exonerate the economics community from any blame.

Corollary 1: The economics profession will never blame monetary policymakers for causing recessions, if the monetary authority reflects the consensus of macroeconomists (as in the US.)

Corollary 2: The economics profession will never predict any problem that could have been prevented by a suitable monetary policy. This means that the consensus forecast will never predict that a recession will commence at some future date.

Much of the current discussion of “the economic crisis” proceeds with the unspoken assumption that the sub-prime loan fiasco is the cause of our current malaise. Indeed, most pundits don’t even see a need to defend that assumption, but rather charge right into explaining how they (we?) could have been so stupid as to allow this financial screw-up to have occurred. After all, it’s obvious that the sub-prime crisis caused the recession, isn’t it?

Actually it isn’t obvious. Indeed, this assumption is only defensible if once the scale of the sub-prime fiasco became apparent for all to see, it became blindingly obvious that we faced a severe economic crisis. But the massive sub-prime crisis became apparent to everyone in late 2007 and early 2008, and yet not only did most economists not predict the current recession (which is now widely expected to be the worst since the Depression), but most economists didn’t even predict a mild recession. All these economists who confidently tell us what we did wrong to get us into the current mess, and even write books about the failures of capitalism, didn’t see “the current mess” coming even when the purported cause was plainly visible to all!

I’ll conclude by repeating a long quotation from the underestimated Paul Einzig, who saw the same mix of incompetence and overconfidence in 1937. (It was from an early post that some of you may not have seen, and I don’t recall anyone commenting on.) This quotation perfectly encapsulates my view of macroeconomists and investors, or “supermen and sub-men” as Einzig calls them:

“On June 9, 1937, this veteran monetary expert [Cassel] published a blood-curdling article in the Daily Mail painting in the darkest colours the situation caused by the superabundance of gold and suggesting a cut in the price of gold to half-way between its present price and its old price as the only possible remedy. He took President Roosevelt sharply to task for having failed to foresee in January 1934 that the devaluation of the dollar by 41 per cent would lead to such a superabundance of gold. If, however, we look at Professor Cassel’s earlier writings, we find that he himself failed to foresee such developments, even at much later dates. We read in the July 1936 issue of the Quarterly Review of the Skandinaviska Kreditaktiebolaget the following remarks by Professor Cassel: ‘There seems to be a general idea that the recent rise in the output of gold has been on such a scale that we are now on the way towards a period of immense abundance of gold. This view can scarcely be correct.’ . . . Thus the learned Professor expected a mere politician to foresee something in January 1934 which he himself was incapable of foreseeing two and a half years later. In fact, it is doubtful whether he would have been capable of foreseeing it at all but for the advent of the gold scare, which, rightly or wrongly, made him see things he had not seen before. It was not the discovery of any new facts, nor even the weight of new scientific argument that converted him and his fellow-economists. It was the subconscious influence of the panic among gold hoarders, speculators, and other sub-men that suddenly opened the eyes of these supermen. This fact must have contributed in no slight degree towards lowering the prestige of economists and of economic science in the eyes of the lay public.” (1937, pp. 26-27.)

When did our economic supermen realize we had a major crisis on our hands? Not in late 2007 when the sub-prime fiasco became apparent. Not in early 2008 when Bear Stearns nearly failed. Not in the summer of 2008 when industrial production and commodity prices began falling rapidly and the real estate crash spread into heartland markets. No, it was in the fall of 2008 when they noticed their 401k accounts tanking, and when the sub-men on Wall Street told them AD was falling fast, that’s when our supermen woke up to the severity of the crisis.

And now they want to tell us that the fault lies with greedy bankers, or deregulation, or regulation, or Greenspan’s monetary policy, or oil price bubbles. They are still unwilling to look in the mirror and ask whether the sharp fall in NGDP in late 2008 might have reflected a monetary policy stance far too contractionary for the needs of the economy. The next generation of economists will look at the appalling NGDP data and have no compunction about pointing fingers where all our macro/money textbooks suggest they should be pointed.

　[点击查看Scott Sumner的英文博客] [Scott Sumner中文博客]