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经济学家须正视群体狂热【保罗•德•格劳威】 [推广有奖]

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dcjzolem 发表于 2009-7-26 14:11:44 |显示全部楼层 |坛友微信交流群

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经济学家须正视群体狂热

保罗•德•格劳威(Paul De Grauwe)

       毫无疑问,宏观经济学正深陷窘境。该领域最为优秀、知名的人物,正围绕着最基本的问题争吵不休。以政府预算赤字为例。目前在英美等国,政府预算赤字占国内生产总值(GDP)的比例已超过10%。一个阵营的宏观经济学家宣称,如不迅速扭转这一局面,如此规模的赤字将导致利率不断上升,并挤出私人投资。巨额赤字非但无法刺激经济,还将导致一场新的衰退,并伴之以通胀大幅攀升。“错!”另一阵营表示。根本不存在什么通胀危险。这种巨额赤字是避免通缩所必需的。压缩赤字将加剧经济中的通缩势头,导致一场新的、更为严重的衰退。

       或者以货币政策为例。一个阵营告诫,流动性大量累积势必导致恶性通胀,因此建议各国央行准备好“退路”。“无稽之谈!”另一个阵营反驳道。流动性的累积不过反映了以下事实:各银行正在囤积资金,以改善自身的资产负债状况。它们坐拥大量现金,但没有将其用于扩大信贷。一旦经济好转,各央行就可以收回流动性,与注资时同样迅速。通胀风险为零。

       双方阵营里都聚集了不少知名诺贝尔奖得主,以增强各自论点的说服力。以往,经济学家就常常意见不合,但这次的语气有所不同。两边的领军人物都毫不犹豫地指责对方无知或不诚实。我从未遇见过这样的情况。

       那又如何?经济学家如此针锋相对有什么关系吗?当然有关系。还是以政府赤字问题为例。如果你要预测长期利率,那么,你相信哪个阵营就大有关系。假如你相信第一个阵营,你会担忧未来的通胀,于是你就会卖出长期国债。其结果是国债价格下跌、利率上升。这样你就把第一个阵营的担忧化为了现实。而假如你相信第二个阵营的说法,你会欣然买入长期国债,使政府得以在利率没有大幅上升的情况下大把花钱,从而促成经济复苏,这正是第二个阵营预料中巨额预算赤字将会产生的结果。

        多数人并不确定哪一方的观点正确。他们犹豫不决。此刻,当到处都出现复苏萌芽时,他们相信认为存在通胀隐患的观点;而彼时,当萌芽枯萎时,他们就转而相信另一种观点。经济学家观点不一,市场参与者就失去了分析和判断形势的理论锚定。说到底,我们所有的预测都采用一种特定的经济模型,来解读数据和预测其未来走向。各种迥然不同的模型的存在,使我们丧失了这种理论锚定,这种情形将加剧市场的波动。

        这种冲突不仅关系到市场参与者,也关系到政策制定者。对于未来4年内政府支出每增加1%,对美国实际GDP将产生多大的影响,两大经济学阵营的估计天差地别。第一个阵营(即李嘉图学派)认为,这一乘数介于0与1%之间,但更接近0,即支出每增加1%,GDP因此增加的百分比将远低于1%,增加的税收收入微不足道。因此,预算赤字将会激增,变得不可维系。

        第二个阵营(即凯恩斯主义者)则预计,在2012年底之前,政府支出每增加1%,所带来的GDP增幅将远大于1%。这正是各国政府所梦寐以求的,因为这样的乘数效应可能导致税收收入增加,使得预算赤字下降。

        经济学家的观点存在如此大的分歧,难怪政策制定者缺乏信心、摇摆不定。美国和法国等国大力奉行凯恩斯主义;德国等其它国家则更为信赖李嘉图主义。我个人认为凯恩斯主义是正确的,但我的意见无足轻重。关键在于,分析上不和谐的声音,有助于解释政策制定者在同一场危机中,为何采取了不同的对策,以及他们达成协同行动为何如此困难。

       如何解决宏观经济学领域的危机?该领域必须进行根本性变革。一些缺陷已暴露无遗。在本轮金融危机之前,多数宏观经济学家都盲目相信,有效市场会自我管理。他们不愿费心把金融市场和银行业纳入他们的模型之中。这是一个重大缺陷。

       但还存在一个更为严重的问题,解决的难度更大。这涉及宏观经济模型的基本范式。主流模型都抱着以下观点:经济行为者都掌握着充足信息,并理解这个世界的深奥与复杂。用行话来说,他们具备“理性预期”。事情不仅如此。由于他们都了解同样的“真相”,所以他们采取同样的行动。因此,要全面描述世界的错综复杂,只需选取单个行为者(“代表性”消费者和“代表性”生产者)的行为制模。如此众多的学者,信奉如此荒谬的观点,实为罕见(其它经济学领域没有被这种不合情理的观点所迷惑,因此没有受到同样的批评。)

      我们需要一种新的宏观经济学,它应从以下假设起步:即个人存在严重的认知局限;他们不太理解自身所处世界的复杂性。由于缺乏理解,就会产生有偏颇的看法,在行为者低估风险时,就会产生过度兴奋的集体行为,继而又将陷入集体的沮丧——此时风险意识明显上升。这些集体行为将无关的风险转变成高度相关的风险。凯恩斯所称的“动物精神”(animal spirits)是造成宏观经济波动的根本力量。


现代宏观经济学的根本失误,是认为经济只是理性行为者微观决策的总和。但经济不光如此。微观决策的相互作用产生了集体行为,而集体行为在微观层面是不可见的。

     用模型表现集体行为仍将十分困难,存在诸多阻力。太多宏观经济学家沉迷于自己的模型,因为他们只想生活在自己所理解的——理性、拥有充足信息的个人的行为——的舒适氛围中。

     用艾萨克•牛顿(Isaac Newton)的话来说,宏观经济学家能够估算出个体理性行为者的举动,但无法推测群体狂热。然而,如果要让宏观经济学重新贴近现实,这一领域的经济学家就必须开始估计这种狂热。虽然困难重重,但这并非放弃尝试的理由。

本文作者是鲁汶大学(university of Leuven)、欧洲政策研究中心(Centre for European Policy Studies)经济学教授

原文附后,本文只供交流,所有版权为金融时报。
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关键词:经济学家 经济学 University Universit European 宏观经济 保罗 经济学家 群体 格劳

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dcjzolem 发表于 2009-7-26 14:12:06 |显示全部楼层 |坛友微信交流群
Warring economists are carried along by the crowd

By Paul De Grauwe



    There can be little doubt. The science of macroeconomics is in deep trouble. The best and the brightest in the field fight over the most basic problems. Take government budget deficits, which now exceed 10 per cent of gross domestic product in countries such as the US and the UK. One camp of macroeconomists claims that, if not quickly reversed, such deficits will lead to rising interest rates and a crowding out of private investment. Instead of stimulating the economy, the deficits will lead to a new recession coupled with a surge in inflation. Wrong, says the other camp. There is no danger of inflation. These large deficits are necessary to avoid deflation. A clampdown on deficits would intensify the deflationary forces in the economy and would lead to a new and more intense recession.



    Or take monetary policy. One camp warns that the build-up of massive amounts of liquidity is the surest road to hyperinflation and advises central banks to prepare an “exit strategy”. Nonsense, the other camp retorts. The build-up of liquidity just reflects the fact that banks are hoarding funds to improve their balance sheets. They sit on this pile of cash but do not use it to increase credit. Once the economy picks up, central banks can withdraw the liquidity as fast as they injected it. The risk of inflation is zero.

Both camps line up an impressive list of Nobel prize-winners to buttress their arguments. Economists have often disagreed in the past, but this time the tone is different. The protagonists do not hesitate to accuse the other camp of ignorance or bad faith. I have never seen anything like this.



    So what? Does it matter that economists disagree so much? It does. Take the issue of government deficits. If you want to forecast the long-term interest rate, it matters a great deal which of the two camps you believe. If you believe the first one, you will fear future inflation and you will sell long-term government bonds. As a result, bond prices will drop and rates will rise. You will have made a reality of the fears of the first camp. But if you believe the story told by the second camp, you will happily buy long-term government bonds, allowing the government to spend without a surge in rates, thereby contributing to a recovery that the second camp predicts will follow from high budget deficits.



    Most people are not sure which campis right. They hesitate. One day, when green shoots are popping up here and there, they believe the story warning about inflation; the next day, when the shoots turn brownish, they believe the other story. Disagreements among economists take away the intellectual anchors around which market participants interpret events and forecast the future. Ultimately, all our forecasts use a particular economic model to interpret data and to forecast their future course. The existence of wildly different models takes away this intellectual anchor and this translates into more market volatility.



    This conflict matters not only for market participants, but also for policymakers. The two camps of economists have wildly different estimates of the effect of a 1 per cent permanent increase in government spending on real US GDP over the next four years. According to the first camp, the Ricardians, the multiplier is closer to zero than to one, ie 1 per cent extra spending generates much less than 1 per cent of extra GDP, producing little extra tax revenue. Thus budget deficits surge and become unsustainable.



    By contrast, the second camp, the Keynesians, predict that the same 1 per cent of extra government spending multiplies into significantly more than 1 per cent of extra GDP each year until the end of 2012. This is the stuff of dreams for governments, because such multiplier effects are likely to generate additional tax income so that budget deficits decline.



    With so much disagreement it is no surprise that policymakers are unsure and vacillate. Some countries, such as the US and France, go all out for the Keynesian story; others, such as Germany, put more faith in the Ricardians. Personally I think the Keynesians are right, but my opinion is irrelevant. The point is that the cacophony of analysis helps to explain why policymakers react in different ways to the same crisis and why it is so difficult for them to come up with co-ordinated action.



    How to resolve this crisis in maco- economics? The field must be revamped fundamentally. Some of its shortcomings are obvious. Before the financial crisis, most macroeconomists were blinded by the idea that efficient markets would take care of themselves. They did not bother to put financial markets and the banking sector into their models. This is a major flaw.



    There is a deeper problem, though, that will be more difficult to resolve. This is the underlying paradigm of macroeconomic models. Mainstream models take the view that economic agents are superbly informed and understand the deep complexities of the world. In the jargon, they have “rational expectations”. Not only that. Since they all understand the same “truth”, they all act in the same way. Thus modelling the behaviour of just one agent (the “representative” consumer and the “representative” producer) is all one has to do to fully describe the intricacies of the world. Rarely has such a ludicrous idea been taken so seriously by so many academics. (Other fields of economics have not been deluded by this implausible idea and therefore do not face the same criticism.)

    We need a new science of macroeconomics. A science that starts from the assumption that individuals have severe cognitive limitations; that they do not understand much about the complexities of the world in which they live. This lack of understanding creates biased beliefs and collective movements of euphoria when agents underestimate risk, followed by collective depression in which perceptions of risk are dramatically increased. These collective movements turn uncorrelated risks into highly correlated ones. What Keynes called “animal spirits” are fundamental forces driving macroeconomic fluctuations.



    The basic error of modern macro- economics is the belief that the economy is simply the sum of microeconomic decisions of rational agents. But the economy is more than that. The interactions of these decisions create collective movements that are not visible at the micro level.



    It will remain difficult to model these collective movements. There is much resistance. Too many macro- economists are attached to their models because they want to live in the comfort of what they understand – the behaviour of rational and superbly informed individuals.



    To paraphrase Isaac Newton, macroeconomists can calculate the motions of a lonely rational agent but not the madness of the crowds. Yet if macroeconomics wants to become relevant again, its practitioners will have to start calculating this madness. It is going to be difficult, but that is no excuse not to try.



    The writer is professor of economics at the university of Leuven and the Centre for European Policy Studies

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zy58164846 发表于 2009-7-26 14:23:31 |显示全部楼层 |坛友微信交流群
中英都有,好问啊!
<B><font color="red">财主都是只买贵的,不买对的</font></B>

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潜悟 发表于 2009-7-26 16:54:58 |显示全部楼层 |坛友微信交流群
感谢分享

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chzsq2009 发表于 2009-7-31 12:08:24 |显示全部楼层 |坛友微信交流群
very good points!

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