1,第三十三章,总需求与总供给 Aggregate Demand and Aggregate Supply,2,But This “Long Run” is a misleading guide to current affaires. “In the long run” we are all dead. Economists set themselves too easy, too useless a task if in tempestuous seasons they can only tell us that when the storm is long past the ocean is flat again. _John Maynard Keynes,Long run and short run,Long-run model potential output, long-run inflation Short-run model current output, current inflation Actual output=long-run trend + short-run fluctuation The short run is defined to be the length of time over which these deviations occur.,3,总需求与总供给 Aggregate Demand and Aggregate Supply,three key facts about short-run economic fluctuations. how the economy in the short run differs from the economy in the long run. how to use the model of aggregate demand and aggregate supply to explain economic fluctuations. how shifts in either aggregate demand or aggregate supply can cause booms and recessions.,4,5,短期经济波动 Short-Run Economic Fluctuations,经济活动年复一年地波动 Economic activity fluctuates from year to year. 在大多数年份里，物品与服务的生产是上升的 In most years production of goods and services rises. 在过去50年，平均来说，美国经济的生产每年增长约3个百分点。 On average over the past 50 years, production in the U.S. economy has grown by about 3 percent per year. 在一些年份，正常的增长没能出现，导致了衰退。 In some years normal growth does not occur, causing a recession.,6,短期经济波动 Short-Run Economic Fluctuations,衰退是实际GDP下降、收入减少、失业上升的时期 A recession is a period of declining real GDP, falling incomes, and rising unemployment. 萧条是严重的衰退 A depression is a severe recession.,7,Real GDP 实际GDP:Figure31-1,1965,1970,1975,1980,1985,1990,1995,2,500,3,000,3,500,4,000,4,500,5,000,5,500,6,000,6,500,$7,000,短期经济波动一瞥 A Look At Short-Run Economic Fluctuations,8,(b) Investment Spending 投资支出,Billions of,1992 Dollars,300,400,500,600,700,800,900,1,000,$1,100,1965,1970,1975,1980,1985,1990,1995,短期经济波动一瞥 A Look At Short-Run Economic Fluctuations,9,(c) Unemployment Rate 失业率,0,2,4,6,8,10,12,1965,1970,1975,1980,1985,1990,1995,短期经济波动一瞥 A Look At Short-Run Economic Fluctuations,10,短期经济波动一瞥：中国 A Look At Short-Run Economic Fluctuations: China,实际GDP,资料来源： 中国国内生产总值核算历史资料，19521995，中国统计年鉴以及作者计算。,11,短期经济波动一瞥：中国 A Look At Short-Run Economic Fluctuations: China,(b) 投资支出,12,中国：GDP、工业生产总值、固定资产投资年增长率的波动,13,关于经济波动的三个关键事实Three Key Facts About Economic Fluctuations,经济波动是不规则和不可预测的。 Economic fluctuations are irregular and unpredictable. 经济当中的波动常常被称作经济周期（或译商业周期） Fluctuations in the economy are often called the business cycle. Trash indicator(The Chicago Tribune ),14,关于经济波动的三个关键事实Three Key Facts About Economic Fluctuations,大多数宏观经济变量一起波动。 Most macroeconomic variables fluctuate together. 大多数衡量某种收入或生产的宏观经济变量几乎同时波动。 Most macroeconomic variables that measure some type of income or production fluctuate closely together. 虽然许多宏观经济变量一起波动，他们波动的幅度并不同。 Although many macroeconomic variables fluctuate together, they fluctuate by different amounts.,15,关于经济波动的三个关键事实Three Key Facts About Economic Fluctuations,随着产出下降，失业上升。 As output falls, unemployment rises. 实际GDP的变化和失业率的变化呈反向关系。Changes in real GDP are inversely related to changes in the unemployment rate. 在衰退时期，失业大幅上升。 During times of recession, unemployment rises substantially.,16,短期与长期有何不同 How the Short Run Differs From the Long Run,大多数经济学家相信，古典理论描述了长期而不是短期中的世界。 Most economists believe that classical theory describes the world in the long run but not in the short run. 货币供给的变化影响长期中的名义变量而非实际变量 Changes in the money supply affect nominal variables but not real variables in the long run. 货币中性（二分法）的假设在研究经济的逐年变化时是不恰当的 The assumption of monetary neutrality is not appropriate when studying year-to-year changes in the economy.,17,经济波动的基本模型 The Basic Model of Economic Fluctuations,我们用两个变量来建立一个模型，以分析短期波动。 Two variables are used to develop a model to analyze the short-run fluctuations. 以实际GDP衡量的经济当中物品与服务的产出。 The economys output of goods and services measured by real GDP. 以CPI或GDP平减指数衡量的整体价格水平。 The overall price level measured by the CPI or the GDP deflator.,18,经济波动的基本模型 The Basic Model of Economic Fluctuations,经济学家使用总需求与总供给模型来解释经济活动围绕其长期趋势的短期波动Economist use the model of aggregate demand and aggregate supply to explain short-run fluctuations in economic activity around its long-run trend.,19,经济波动的基本模型 The Basic Model of Economic Fluctuations,总需求曲线表示家庭、企业或政府在任一价格水平上想要购买的物品与服务的数量。 The aggregate demand curve shows the quantity of goods and services that households, firms, and the government want to buy at each price level.,20,经济波动的基本模型 The Basic