昆山兵希小学:The Great Moderation （1）

One of the most striking features of the economic landscape over the past twenty years or so has been a substantial decline in macroeconomic volatility. In a recent article, Olivier Blanchard and John Simon (2001) documented that the variability of quarterly growth in real output (as measured by its standard deviation) has declined by half since the mid-1980s, while the variability of quarterly inflation has declined by about two thirds.¹ Several writers on the topic have dubbed this remarkable decline in the variability of both output and inflation "the Great Moderation." Similar declines in the volatility of output and inflation occurred at about the same time in other major industrial countries, with the recent exception of Japan, a country that has faced a distinctive set of economic problems in the past decade.

几个主要的工业国同时发生了这种情景：通胀、产出的波动性减弱。

Reduced macroeconomic volatility has numerous benefits. Lower volatility of inflation improves market functioning, makes economic planning easier, and reduces the resources devoted to hedging inflation risks. Lower volatility of output tends to imply more stable employment and a reduction in the extent of economic uncertainty confronting households and firms. The reduction in the volatility of output is also closely associated with the fact that recessions have become less frequent and less severe.²
通胀下降的几点好处：提升市场效率、使得经济决策更加容易、减少了对冲通胀风险所需要的资源 Why has macroeconomic volatility declined? Three types of explanations have been suggested for this dramatic change; for brevity, I will refer to these classes of explanations as structural change, improved macroeconomic policies, and good luck. Explanations focusing on structural change suggest that changes in economic institutions, technology, business practices, or other structural features of the economy have improved the ability of the economy to absorb shocks. Some economists have argued, for example, that improved management of business inventories, made possible by advances in computation and communication, has reduced the amplitude of fluctuations in inventory stocks, which in earlier decades played an important role in cyclical fluctuations.³ The increased depth and sophistication of financial markets, deregulation in many industries, the shift away from manufacturing toward services, and increased openness to trade and international capital flows are other examples of structural changes that may have increased macroeconomic flexibility and stability.  结构变化层面的解释：技术水平、商业实践、以及经济中的其他结构性因素提升了经济承受短期冲击的能力。例如：存货管理的提升减弱了存货周期波动影响。此外，金融市场的深度发展。 The second class of explanations focuses on the arguably improved performance of macroeconomic policies, particularly monetary policy. The historical pattern of changes in the volatilities of output growth and inflation gives some credence to the idea that better monetary policy may have been a major contributor to increased economic stability. As Blanchard and Simon (2001) show, output volatility and inflation volatility have had a strong tendency to move together, both in the United States and other industrial countries. In particular, output volatility in the United States, at a high level in the immediate postwar era, declined significantly between 1955 and 1970, a period in which inflation volatility was low. Both output volatility and inflation volatility rose significantly in the 1970s and early 1980s and, as I have noted, both fell sharply after about 1984. Economists generally agree that the 1970s, the period of highest volatility in both output and inflation, was also a period in which monetary policy performed quite poorly, relative to both earlier and later periods (Romer and Romer, 2002).⁴ Few disagree that monetary policy has played a large part in stabilizing inflation, and so the fact that output volatility has declined in parallel with inflation volatility, both in the United States and abroad, suggests that monetary policy may have helped moderate the variability of output as well.  现象背后的政策根源：70年代高度波动的经济背后是政策的拙劣的表现。 The third class of explanations suggests that the Great Moderation did not result primarily from changes in the structure of the economy or improvements in policymaking but occurred because the shocks hitting the economy became smaller and more infrequent. In other words, the reduction in macroeconomic volatility we have lately enjoyed is largely the result of good luck, not an intrinsically more stable economy or better policies. Several prominent studies using distinct empirical approaches have provided support for the good-luck hypothesis (Ahmed, Levin, and Wilson, 2002; Stock and Watson, 2003).

Explanations of complicated phenomena are rarely clear cut and simple, and each of the three classes of explanations I have described probably contains elements of truth. Nevertheless, sorting out the relative importance of these explanations is of more than purely historical interest. Notably, if the Great Moderation was largely the result of good luck rather than a more stable economy or better policies, then we have no particular reason to expect the relatively benign economic environment of the past twenty years to continue. Indeed, if the good-luck hypothesis is true, it is entirely possible that the variability of output growth and inflation in the United States may, at some point, return to the levels of the 1970s. If instead the Great Moderation was the result of structural change or improved policymaking, then the increase in stability should be more likely to persist, assuming of course that policymakers do not forget the lessons of history.

My view is that improvements in monetary policy, though certainly not the only factor, have probably been an important source of the Great Moderation. In particular, I am not convinced that the decline in macroeconomic volatility of the past two decades was primarily the result of good luck, as some have argued, though I am sure good luck had its part to play as well. In the remainder of my remarks, I will provide some support for the "improved-monetary-policy" explanation for the Great Moderation. I will not spend much time on the other two classes of explanations, not because they are uninteresting or unimportant, but because my time is limited and the structural change and good-luck hypotheses have been extensively discussed elsewhere.⁵ Before proceeding, I should note that my views are not necessarily those of my colleagues on the Board of Governors or the Federal Open Market Committee.

Ahmed, Shaghil, Andrew Levin, and Beth Anne Wilson (2002). "Recent U.S. Macroeconomic Stability: Good Policies, Good Practices, or Good Luck?" Board of Governors of the Federal Reserve System, International Finance Discussion Paper 2002-730 (July).

Albanesi, Stefania, V.V. Chari, and Lawrence Christiano (2003). "Expectation Traps and Monetary Policy," Federal Reserve Bank of Minneapolis, Research Department Staff Report 319 (August).

Barsky, Robert, and Lutz Kilian (2001). "Do We Really Know That Oil Caused the Great Stagflation? A Monetary Alternative," in Ben Bernanke and Kenneth Rogoff, eds., NBER Macroeconomics Annual, Cambridge, Mass.: MIT Press for NBER, pp. 137-82.

Bernanke, Ben (2003). "'Constrained Discretion' and Monetary Policy," before the Money Marketeers of New York University, New York, New York, February 3.

Bernanke, Ben (2004). "Fedspeak," at the meetings of the American Economic Association, San Diego, California, January 3.