哈佛大学教授：货币政策之谜(哈佛大学政治)

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哈佛大学经济学教授Robert J. Barro近日发文称，自从联邦基金利率在20世纪80年代初达到22%的峰值以来，美国的通货膨胀率一直保持在较低且稳定的水平，这使得许多人相信，仅仅是再次加息的威胁就能控制通货膨胀。

但没有人真正知道为什么通胀会被抑制这么久。

哈佛大学教授：货币政策之谜图片 | 视觉中国战后经济史的一个显著特征是，自20世纪80年代中期以来，美国和许多其他国家遏制了通货膨胀。

在此之前，美国的通胀率(基于个人消费支出的平减指数)在20世纪70年代平均为每年6.6%，在1979年至1980年超过了10%。

One of the remarkable features of post-war economic history has been the taming of inflation in the United States and many other countries since the mid-1980s. Before then, the US inflation rate (based on the deflator for personal consumption expenditures) averaged 6.6% per year during the 1970s, and exceeded 10% in 1979-1980.20世纪70年代初期和中期，美国总统理查德?尼克松(Richard Nixon)和杰拉尔德?福特(Gerald Ford)试图通过对价格控制和告诫的错误结合，以及适度的货币紧缩来遏制通胀。

但随后，美国总统吉米?卡特(Jimmy Carter)在最初维持这种做法后，任命保罗?沃尔克(Paul Volcker)为美联储主席。

在沃尔克的领导下，美联储很快开始将短期名义利率提高到任何可能降低通胀的水平。

In the early- and mid-1970s, Presidents Richard Nixon and Gerald Ford tried to curb inflation with a misguided combination of price controls and exhortation, along with moderate monetary restraint. But then came President Jimmy Carter, who, after initially maintaining this approach, appointed Paul Volcker to chair the US Federal Reserve in August 1979. Under Volcker, the Fed soon began to raise short-term nominal interest rates to whatever level it would take to bring down inflation.1981年1月之后，在罗纳德·里根(Ronald Reagan)总统的支持下，沃尔克不顾强烈的政治反对，坚持了这一做法。

同年7月，联邦基金利率达到22%的峰值。

这项政策奏效了：从1983年到1989年，年通货膨胀率急剧下降到3.4%的平均水平。

美联储以极端的形式满足了后来被称为泰勒原则(或者更恰当地说，沃尔克原则)的要求，即联邦基金利率的增幅大于通胀率的增幅。

Volcker, backed by President Ronald Reagan after January 1981, stuck with this approach, despite intense political opposition, and that July the federal funds rate peaked at 22%. The policy worked: annual inflation fell sharply to an average of just 3.4% from 1983 to 1989. The Fed had satisfied in extreme form what later became known as the Taylor Principle (or, more appropriately, the Volcker Principle), whereby the federal funds rate increases by more than the rise in the inflation rate.从那时起，美联储主要通过控制短期名义利率，尤其是联邦基金利率，来引导货币政策。

2008年金融危机后，由于联邦基金利率接近零的下限，美联储对短期借贷成本的控制能力受到损害，于是，美联储采取了前瞻性指引和量化宽松政策(QE)补充了其主要政策工具。

Since then, the Fed has guided monetary policy primarily through control over short-term nominal interest rates, especially the federal funds rate. When its power over short-term borrowing costs was compromised following the 2008 financial crisis – because the federal funds rate approached its zero lower bound – the Fed supplemented its main policy instrument with forward guidance and quantitative easing (QE).从美国过去几十年的通胀率来看，美联储的货币政策成效显著。

自2010年以来，年均通胀率仅为1.5%，略低于美联储常说的2%的目标，而且一直非常稳定。

然而，问题是这是如何实现的。

通胀率之所以保持在较低水平，是因为所有人都认为，只要通胀率显著高于1.5-2%的区间，就会引发联邦基金利率的大幅上升吗?Judging by the US inflation rate over past decades, the Fed’s monetary policy has worked brilliantly. Annual inflation has averaged only 1.5% per year since 2010, slightly below the Fed’s oft-expressed target of 2%, and has been strikingly stable. And yet, the question is how this was achieved. Did inflation remain subdued because everyone believed that anything significantly above the 1.5-2% range would trigger a sharp hike in the federal funds rate?有大量的研究是关于联邦基金利率的变化如何影响经济的。

例如，中村惠美(Emi Nakamura)和乔恩?斯坦森(Jon Steinsson) 2018年在《经济学季刊》(Quarterly Journal of Economics)上发表的一篇论文表示，紧缩性货币冲击，以及联邦基金利率的意外上升，会在3至5年内推高美国国债收益率，其峰值效应为两年。

(扩张性冲击的结果是对称的。

)这些影响大多适用于实际利率，并体现在指数债券和传统国债中。

收缩性冲击对预期通胀率的影响为负，但规模适中，仅在3-5年后才开始显著显现。

There is a large body of research into how changes in the federal funds rate influence the economy. A 2018 paper by Emi Nakamura and Jón Steinsson in the Quarterly Journal of Economics, for example, finds that a contractionary monetary shock – an unanticipated rise in the federal funds rate – raises yields on Treasury securities over a 3-5-year horizon, with a peak effect at two years. (Results for expansionary shocks are symmetric.) Most of these effects apply to real interest rates, and show up in indexed bonds as well as conventional Treasuries. The effect of a contractionary shock on the prospective inflation rate is negative but moderate in size, and sets in significantly only after 3-5 years.尽管联邦基金利率的意外增长通常被贴上紧缩的标签，但中村和斯坦森发现，在意外加息之后，“对产出增长的预测”实际上会上升。

也就是说，加息预示着更高的增长，而降息则预示着更低的增长。

这种情况可能会发生，因为美联储通常会在得知经济比预期强劲时加息，而在怀疑经济比此前预期疲软时降息。

Although unexpected increases in the federal funds rate are conventionally labeled as contractionary, Nakamura and Steinsson find that “forecasts about output growth” actually rise for the year following an unexpected rate hike. That is, a rate increase predicts higher growth, and a decrease predicts lowergrowth. This pattern likely occurs because the Fed typically raises interest rates when it gets information that the economy is stronger than expected, and it cuts rates when it suspects that the economy is weaker than it previously thought.同一篇论文还发现，出乎意料的联邦基金利率上调对股市不利(反之亦然)，这符合许多金融评论员的根深蒂固的观点，更不用说美国总统唐纳德?特朗普(Donald Trump)了。

作者估计，尽管预计实际GDP增速将下降，但出人意料的降息50个基点将使标准普尔500指数上涨约5%。

可能的原因是，未来3至5年，美国国债等竞争性金融工具的预期实际回报率将下降。

这种贴现率效应掩盖了预期未来实际收益下降对股价的负面影响。

The same paper also finds that an unanticipated rise in the federal funds rate is bad for the stock market (and vice versa), which accords with the deeply held views of many financial commentators, not to mention US President Donald Trump. The authors estimate that an unanticipated rate cut of 50 basis points raises the S&P 500 stock-market index by about 5%, even though projected real GDP growth declines. The likely reason is the decrease in expected real returns on competing financial instruments, such as Treasury bonds, over the next 3-5 years. This discount-rate effect overshadows the negative influence on stock prices from lower expected future real earnings.但是，同样令人困惑的是，美联储如何能够依靠一种似乎只有微弱和滞后效应的政策工具，将通胀维持在每年1.5%的水平。

据推测，如果通胀率大幅高于1.5-2%的区间，美联储将启动沃尔克在上世纪80年代初实施的那种短期名义利率大幅上调，而这些变化将对通胀产生重大而迅速的负面影响。

同样，如果通胀率远低于目标水平，甚至可能变为负值，美联储将大幅降息，或者，在触及零利率下限后，使用替代的扩张性政策，这将对通胀产生重大而迅速的积极影响。

But, again, the puzzle is how the Fed can keep inflation steady at 1.5?2% per year by relying on a policy tool that seems to have only weak and delayed effects. Presumably, if inflation were to rise substantially above the 1.5-2% range, the Fed would initiate the type of dramatic increases in short-term nominal interest rates that Volcker carried out in the early 1980s, and these changes would have major and rapid negative effects on inflation. Similarly, if inflation were to fall well below target, perhaps becoming negative, the Fed would sharply cut rates – or, after hitting the zero-lower bound, use alternative expansionary policies – and this would have major and rapid positive effects on inflation.根据这种观点，美联储做出极端反应的威胁的可信性意味着，它实际上不必重复沃尔克时代的政策。

自那以来，利率变动与通胀之间的关联不大，但更剧烈变动的假设可能性仍然很大。

According to this view, the credible threat of extreme responses from the Fed has meant that it does not actually have to repeat the Volcker-era policy. Rate changes since that time have had modest associations with inflation, but the hypothetical possibility of muchsharper changes has remained powerful.坦率地说，我对这种解释不满意。

这就好比说，通胀率之所以被抑制，是因为它本来就是如此。

毫无疑问，一个关键因素是实际和预期通胀率都很低，而这两者是密切相关的。

但这表明，目前处于低位且稳定的实际和预期通胀背后的货币政策将继续发挥作用，直到突然失效。

Frankly, I am unhappy with this explanation. It is like saying that the inflation rate is subdued because it just is. And, no doubt, a key factor is that actual and expected inflation have both been low – the two are intimately connected twins. But this suggests that the monetary policy behind today’s low and stable actual and expected inflation will keep working until, suddenly, it doesn’t.作者：Robert J. BarroRobert J. Barro是哈佛大学经济学教授，美国企业研究所访问学者。

他是《宗教财富：信仰和归属的政治经济学》的合著者（与Rachel M. McCleary合著）。

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