通货膨胀与失业之间的短期权衡取舍 35 经济学原理 [美]曼昆 著 上海财经大学 This chapter traces the history of economists’ thinking about the relationship between inflation and unemployment. It is the last of a three-chapter sequence on short-run economic fluctuations. It builds on three key elements of the preceding two chapters: 1) The upward-sloping SRAS curve, and how it shifts in response to changes in expectations 2) The ability of monetary policy to shift the AD curve and affect real variables in the short run 3) The classical dichotomy, long-run monetary neutrality, and vertical LRAS curve While this chapter is not easy, most students find it less difficult than the two preceding chapters. 上海财经大学

本章我们将探索这些问题的答案： 短期内通货膨胀与失业有什么关系？长期内呢？ 什么因素会改变通货膨胀与失业之间的这种关系？ 减少通货膨胀的短期成本是什么？ 为什么在20世纪90年代美国的通货膨胀与失业率都很低？ 1

介绍 在长期中，通货膨胀与失业是不相关的： 经济学十大原理之一： 社会面临通货膨胀和失业之间的短期权衡取舍 通货膨胀率主要取决于货币供给的增长率 自然失业率取决于最低工资法，工会的市场势力，效率工资以及寻找工作的有效性 经济学十大原理之一： 社会面临通货膨胀和失业之间的短期权衡取舍 通货膨胀与失业之间的短期权衡取舍

菲利普斯曲线 菲利普斯曲线：一条表示通货膨胀与失业之间短期权衡取舍的曲线 1958年，菲利普斯（A.W. Phillips）说明英国名义工资增长率与失业率之间的负相关关系 1960年，保罗·萨缪尔森（Paul Samuelson）与罗伯特·索洛（Robert Solow）发现美国通货膨胀与失业之间也存在这种负相关关系，他们把它称为“菲利普斯曲线” 通货膨胀与失业之间的短期权衡取舍

菲利普斯曲线的推导 假设今年 P = 100 下面的图形表示明年可能出现的两种结果： A. 总需求低，物价水平上升缓慢（低通货膨胀），低产出，高失业 B. 总需求高，物价水平上升快（高通货膨胀），高产出，低失业 “Suppose P = 100 this year” provides an anchor to the analysis in the graphs on the following slide. At this point, remind students that output and unemployment are negatively related over business cycles (one of the “three facts about economic fluctuations” from the chapter entitled “aggregate demand and aggregate supply”). 通货膨胀与失业之间的短期权衡取舍 4

菲利普斯曲线的推导 A. 总需求低，低通货膨胀，高失业率 B. 总需求高，高通货膨胀，低失业率 PC Y P 失业率 通货膨胀率 AD2 SRAS PC 4% 5% B 105 Y2 B AD1 Y1 103 A 6% 3% A Assume P = 100 this year. If aggregate demand next year is low – reflecting, for example, slow money growth – then outcome A will occur next year. In outcome A, P = 103 next year, so the inflation rate from this year to next equals 3%. Output (Y1) is relatively low, so unemployment is relatively high at 6%. Instead, if aggregate demand next year is high – reflecting, for example, rapid money growth – then outcome B will occur next year. In outcome B, P = 105 next year, so the inflation rate from this year to next equals 5%. Output (Y2) is higher, so unemployment is lower (4%). B. 总需求高，高通货膨胀，低失业率 通货膨胀与失业之间的短期权衡取舍 5

菲利普斯曲线：一个政策菜单？ 由于财政政策与货币政策都能影响总需求，菲利普斯曲线给政策制定者提供了一个可以选择各种经济结果的菜单： 低失业与高通货膨胀 低通货膨胀与高失业 两者之间的任何情况 20世纪60年代，美国的数据支持菲利普斯曲线。许多人认为菲利普斯曲线是稳定可信的 通货膨胀与失业之间的短期权衡取舍

在20世纪60年代， 美国政策制定者选择以提高通货膨胀率为代价来降低失业率 菲利普斯曲线的证据？ 通货膨胀率 (年百分比) 在20世纪60年代， 美国政策制定者选择以提高通货膨胀率为代价来降低失业率 68 The data almost perfectly trace out a downward-sloping Phillips curve. But what’s important here is not just the negative slope, but the economy’s movement over the years: Fiscal policy was expansionary, in part to finance the Vietnam war. To keep interest rates low, the Fed made monetary policy expansionary as well. As a result, aggregate demand grew over the 1960s. You can see this if you follow the points year by year: inflation gradually creeps up while unemployment is falling, which is exactly what was depicted on the graphs we used to derive the Phillips curve. 66 67 62 65 1961 64 63 失业率（百分比） 通货膨胀与失业之间的短期权衡取舍

垂直的长期菲利普斯曲线 1968年，米尔顿·弗里德曼和爱德蒙·费尔普斯指出通货膨胀与失业之间的权衡取舍是暂时的 自然率假说：认为无论通货膨胀率如何，失业最终要回到其正常率或自然律的观点 这是基于古典二分法和垂直的长期总供给曲线 In the face of what many considered overwhelming evidence for the stability of the downward-sloping Phillips curve, Friedman and Phelps (working separately) boldly asserted that any tradeoff would be purely temporary. Their logic? The Classical Dichotomy and the vertical LRAS curve. 通货膨胀与失业之间的短期权衡取舍 8

在长期中，货币增长越快只会导致通货膨胀率越高 垂直的长期菲利普斯曲线 在长期中，货币增长越快只会导致通货膨胀率越高 Y P 失业率 通货膨胀 LRAS LRPC AD2 P2 高通胀 AD1 P1 The greater the expansion of the money supply, the faster AD will shift to the right, resulting in a larger increase in prices – i.e. higher inflation. But this higher inflation will not produce lower unemployment: in the long run, unemployment always goes to its natural rate whether inflation is high or low. In the long run, faster money growth only causes faster inflation. 低通胀 自然产量率 自然失业率 9 9

使理论与证据一致 来自20世纪60年代的证据： 菲利普斯曲线向右下方倾斜 理论（弗里德曼与费尔普斯）： 长期菲利普斯曲线是垂直的 来自20世纪60年代的证据： 菲利普斯曲线向右下方倾斜 理论（弗里德曼与费尔普斯）： 长期菲利普斯曲线是垂直的 为使理论与证据相一致，弗里德曼与费尔普斯引进了一个新的变量：预期通货膨胀 – 衡量人们预期物价总水平的变动幅度 通货膨胀与失业之间的短期权衡取舍

菲利普斯曲线方程 a 在短期中 央行可以使实际通货膨胀高于预期通货膨胀，而使失业率降到自然失业率以下 = – a 实际通货膨胀 预期通货膨胀 在短期中 央行可以使实际通货膨胀高于预期通货膨胀，而使失业率降到自然失业率以下 在长期中 预期通货膨胀与现实相符，失业率回到自然失业率，无论通货膨胀是高还是低 This equation is essentially the equation for aggregate supply introduced in the “aggregate demand and aggregate supply” chapter. The coefficient a is a positive number that measures the relationship between unexpected inflation and deviations of unemployment from its natural rate: A 1% increase in inflation causes the unemployment rate to fall by a (for given values of the natural rate and expected inflation). Point out to students that this equation – and its coefficient a – are very similar to the equation for the aggregate supply curve in the chapter “Aggregate Demand and Aggregate Supply.” If the Fed wants to reduce unemployment below the natural rate, it has to surprise people with higher-than-anticipated inflation. The result will be lower unemployment – but only until people adjust their expectations to the new reality of higher inflation. Eventually, expectations catch up with reality – i.e., people see that inflation is higher than they’d expected, so they adjust their expectations upward. 通货膨胀与失业之间的短期权衡取舍 11

预期通货膨胀如何移动菲利普斯曲线 最初，预期通货膨胀与实际通货膨胀都等于3%, 失业率 =自然率 (6%) 央行使实际通货膨胀比预期通货膨胀高出2%，失业率降到4% 在长期中，预期通货膨胀会上升到5%，菲利普斯曲线向右上方移动，失业率回到自然失业率水平 失业率 通货膨胀率 LRPC 6% PC2 PC1 B C 4% 5% A 3% When people adjust their inflation expectations upward, then the PC shifts up: each value of the u-rate is associated with a higher inflation rate. Of course, we can extrapolate this: Suppose the Fed wants to PERMANENTLY keep unemployment at 4%. It must continually raise inflation above expectations. Expectations will keep adjusting upward, so the Fed will have to keep raising the inflation rate faster than expectations are adjusting. Inflation spirals upward as a result of the attempt to keep unemployment at 4%. Before long, people will come to expect not only higher inflation but ever-increasing inflation, and they will factor this into their contracts. It will be extremely difficult for the Fed to continue this game. Ultimately, unemployment has to return to the natural rate, yet the economy will end up with something approaching hyperinflation and the costs it imposes on society. 通货膨胀与失业之间的短期权衡取舍 12

自然失业率 = 5%，预期通货膨胀率 = 2%，在菲利普斯曲线方程中的 a = 0.5 主动学习 1 一个数值例子 自然失业率 = 5%，预期通货膨胀率 = 2%，在菲利普斯曲线方程中的 a = 0.5 A. 画出长期菲利普斯曲线 B. 找出实际通货膨胀为 0%，6%时的失业率，并画出短期菲利普斯曲线 C. 如果预期通货膨胀率上升至 4%。重复B过程 D. 如果自然失业率下降到 4%，画出新的长期菲利普斯曲线，再重复B过程 For many students, working a concrete numerical example helps make the concepts clearer. This exercise leads students to see for themselves how the Phillips curve shifts in response to changes in expected inflation and the natural rate of unemployment. If you would like to get through the chapter more quickly, you can delete Part D of the question from this slide (and the corresponding parts of the answers on the next slide). 13

预期通货膨胀率的上升使菲利普斯曲线向右移动 主动学习 1 参考答案 PCB LRPCD LRPCA 预期通货膨胀率的上升使菲利普斯曲线向右移动 PCD PCC 自然失业率的下降使两条曲线都向左移动 The subscript in each curve’s label refers to the corresponding part of the question. For example, the answer to part C is the downward-sloping dark red curve labeled PCC. Parts A and B comprise a benchmark, an initial set of LR and SR Phillips curves, against which we will compare - the effects of an increase in expected inflation (Part C) - the effects of a fall in the natural rate (Part D) 14

菲利普斯曲线的破灭 20世纪70年代初期：虽然通货膨胀率很高，失业率还是在上升 费里德曼和菲利普斯解释：人们对通货膨胀的预期赶上了现实 通货膨胀率 (年百分比) 20世纪70年代初期：虽然通货膨胀率很高，失业率还是在上升 费里德曼和菲利普斯解释：人们对通货膨胀的预期赶上了现实 73 69 71 70 68 72 This chart adds a few additional years of data to the previous data chart. From 1969 to 1973, inflation and unemployment BOTH INCREASE. People were adjusting their expectations of inflation upward, causing the Phillips curve to shift upward. This is consistent with Friedman and Phelps’ work, which was looking increasingly convincing to economists and others. 66 67 62 65 1961 64 63 失业率 (百分比) 通货膨胀与失业之间的短期权衡取舍

菲利普斯曲线的移动：供给冲击 供给冲击：直接改变企业的成本和价格，使经济中的总供给曲线移动，进而使菲利普斯曲线移动的事件 例如：石油价格的大幅上涨 通货膨胀与失业之间的短期权衡取舍

不利供给冲击如何移动菲利普斯曲线 SRAS向左移动，价格上升，产出与就业下降 PC2 PC1 Y P 失业率 通货膨胀率 PC2 SRAS2 AD SRAS1 PC1 Y2 B P2 B A Y1 P1 A In the chapter “Aggregate Demand and Aggregate Supply,” students learned that adverse supply shocks – like oil price increases – shift the SRAS curve to the left, causing “stagflation” (falling output and rising prices). We see here that adverse supply shocks also shift the short-run Phillips curve to the right and worsen the tradeoff between inflation and unemployment. 随着菲利普斯曲线向右移动，通货膨胀率与失业率都上升 通货膨胀与失业之间的短期权衡取舍 17

20世纪70年代的石油价格冲击 美联储用更快的货币增长来抵消1973年的第一次石油价格冲击 $ 3.56 1/1973 每桶原油价格 美联储用更快的货币增长来抵消1973年的第一次石油价格冲击 结果： 高预期通货膨胀使菲利普斯曲线进一步向右移动 1979年，石油价格再次上涨，联储面临更艰难的权衡取舍 10.11 1/1974 14.85 1/1979 32.50 1/1980 38.00 1/1981 Data – the spot oil price of West Texas Intermediate Original source: Dow Jones & Company Where I found this data: http://research.stlouisfed.org/fred2/ 通货膨胀与失业之间的短期权衡取舍 18

20世纪70年代的石油价格冲击 供给冲击和预期通货膨胀率的上升使联储面临更艰难的权衡取舍 通货膨胀率 (年百分比) 失业率 (百分比) 81 通货膨胀率 (年百分比) 供给冲击和预期通货膨胀率的上升使联储面临更艰难的权衡取舍 81 75 74 80 79 78 77 73 76 From 1973-75, inflation and unemployment both rise sharply, reflecting the upward shifts of the PC in response to the first supply shock and the Fed’s accommodating monetary policy. During the mid-1970s, oil prices were relatively stable for a couple years, and the economy began its self-correction process with SRAS shifting down. On the graph on this slide, we see inflation coming down in 1976 and unemployment falling slightly as the economy starts to come out of the recession. From 1976-79, it appears that policy was being used to push the economy up its new, higher Phillips curve to a point with lower unemployment but higher inflation. In 1979, the revolution in Iran and renewed OPEC activity led to a second huge spike in oil prices, which further worsened the unemployment-inflation tradeoff. From 1979 to 1981, the graph shows both unemployment and inflation rising. 1972 失业率 (百分比) 通货膨胀与失业之间的短期权衡取舍

降低通货膨胀的代价 反通货膨胀：降低通货膨胀率 为降低通货膨胀率，美联储必须降低货币增长率，以减少总需求 短期：产出下降，失业上升 长期：产出与失业回到各自的自然率水平 通货膨胀与失业之间的短期权衡取舍

反通货膨胀的货币政策 紧缩性货币政策使经济从A 点移到B点 随着时间的推移， 预期通货膨胀下降，菲利普斯曲线向下移动 在长期中，经济回到 随着时间的推移， 预期通货膨胀下降，菲利普斯曲线向下移动 在长期中，经济回到 C点：自然失业率， 较低的通货膨胀率 失业率 通货膨胀率 LRPC PC1 PC2 A B C 自然失业率 通货膨胀与失业之间的短期权衡取舍

降低通货膨胀的代价 反通货膨胀要忍受一段时间的高失业与低产量 牺牲率：在通货膨胀减少一个百分点的过程中每年产量损失的百分点数 牺牲率一般估算：5 就是说通货膨胀率每减少一个百分点，在这种转变中每年必须牺牲的产量是 5% 这种降低通货膨胀的代价可以在几年之内分摊，例如：为使通货膨胀率降低6个百分点 可以牺牲一年GDP 的30% 或者牺牲三年内每年GDP的10% 通货膨胀与失业之间的短期权衡取舍

理性预期与无代价地反通货膨胀 理性预期：当人们在预测未来时，可以充分运用他们所拥有的全部信息，包括有关政府政策的信息的理论 早期支持者： 罗伯特·卢卡斯（Robert Lucas），托马斯·萨金特 (Thomas Sargent)，罗伯特·巴罗（Robert Barro） 意味着反通货膨胀的成本可能要小得多…… 通货膨胀与失业之间的短期权衡取舍

理性预期与无代价地反通货膨胀 如果联储向每个人做出降低通货膨胀的可信承诺 那预期通货膨胀会下降，短期菲利普斯曲线向下移动 结果：反通货膨胀引起的失业比传统牺牲率估计的要小 通货膨胀与失业之间的短期权衡取舍

沃尔克的反通货膨胀 美联储主席保罗·沃尔克 在经济高通货膨胀与高失业的1979年底被任命为美联储主席 转而实行反通货膨胀的政策 1981-1984年： 由于当时实行扩张性的财政政策，联储必须实行非常紧缩的货币政策来降低通货膨胀 反通货膨胀成功：通货膨胀率从10% 降到 4%， 但却以高失业率为代价…… By the end of the 1970s, the Phillips curve had shifted far to the right, substantially worsening the Fed’s short-run tradeoff between inflation and unemployment. Volcker knew that monetary policy had to change. 通货膨胀与失业之间的短期权衡取舍 25

沃尔克的反通货膨胀 反通货膨胀的代价非常高 在1982-1983年，失业率接近10% 通货膨胀率 (年百分比) 失业率 (百分比) 81 通货膨胀率 (年百分比) 反通货膨胀的代价非常高 在1982-1983年，失业率接近10% 81 80 1979 82 84 Volcker succeeded in bringing inflation down but at the cost of the deepest recession since the Great Depression. Imagine a downward-sloping line going through the points from 1980 to 1982 or 1983. This imaginary line is the short-run Phillips curve at its highest level. The Fed pursued a policy that took the economy on a path very similar to that shown in the diagram a few slides back on a slide entitled “Disinflationary Monetary Policy.” 83 87 85 86 失业率 (百分比) 通货膨胀与失业之间的短期权衡取舍

格林斯潘时代 1986年：石油价格下降了50% 1989 -1990年： 失业率下降，通货膨胀上升，美联 储提高利率，引起经济的微小衰退 1989 -1990年： 失业率下降，通货膨胀上升，美联 储提高利率，引起经济的微小衰退 20世纪90年代： 失业率和通货膨胀都下降 2001年：不利的需求冲击使美国经济经历了十年中的第一次衰退，政策决策者用扩张性的货币政策与扩张性的财政政策帮助结束了这次衰退 格林斯潘 联邦公开市场委员会主席 1987.8-2006.1 通货膨胀与失业之间的短期权衡取舍

在格林斯潘担任美联储主席的大部分时间里，通货膨胀与失业率都较低 格林斯潘时代 通货膨胀率 (年百分比) 在格林斯潘担任美联储主席的大部分时间里，通货膨胀与失业率都较低 90 05 In this period, inflation and unemployment were lower and less variable than previous periods. A few highlights: 1990-92: Rising unemployment that resulted from the first recession of this period. 1992-98: Unemployment falls without a corresponding increase in inflation – in fact, inflation edged lower. 1998-2000: Small increase in inflation while unemployment continues its downward march. 2001-2003: Rising unemployment following the second recession of this period 2003-2006: Expansionary fiscal and monetary policy reduce unemployment, at a cost of slightly higher inflation. 1987 06 2000 92 94 96 02 98 失业率 (百分比) 通货膨胀与失业之间的短期权衡取舍

伯南克的挑战 总需求冲击： 次贷危机，住房价格下降，大量丧失赎权，金融机构处于困境 总供给冲击： 食品/农产品价格上涨，如每蒲式耳玉米的价格从2005-2006年的2.10美元上涨到2008年5月的5.76美元 石油价格上涨 每桶原油价格：2004年2月的35美元到2008年6月的134美元 从2007年6月到2008年6月： 失业率从4.6%上升到 5.5% CPI通货膨胀率从2.6%上升到4.9% This slide corresponds to a section, new to the 5th edition, appearing near the end of the chapter. Data sources: Oil price data from FRED http://research.stlouisfed.org/fred2/series/OILPRICE?cid=98 Corn price data from USDA Economic Research Service, Table 18 http://www.ers.usda.gov/Publications/AgOutlook/AOTables/ 通货膨胀与失业之间的短期权衡取舍

结论 本章的理论是20世纪许多最优秀的经济学家的思想 他们告诉我们通货膨胀与失业率： 在长期中是无关的 短期中是负相关的 受预期影响，预期在经济从短期向长期调整过程中起着相当重要的作用 通货膨胀与失业之间的短期权衡取舍

内容提要 菲利普斯曲线描述了通货膨胀与失业之间的短期权衡取舍 在长期中，通货膨胀与失业之间并不存在权衡取舍：通货膨胀率取决于货币增长率，而失业率等于自然失业率 供给冲击与预期通货膨胀的变动会使短期菲利普斯曲线发生移动，从而给决策者一个更有利或不利的通货膨胀和失业之间的权衡取舍 31

内容提要 当美联储紧缩货币供给增长以降低通货膨胀时，它使经济沿着短期菲利普斯曲线移动，这就引起暂时的高失业。然而在长期中，预期调整与现实一致，失业率回到自然率 一些经济学家认为，可信任的低通货膨胀承诺可以通过引起预期的迅速调整而降低反通货膨胀的代价 32