宏观经济学：第10章 总需求I

1、slide 0slide 1slide 2the IS curve, and its relation tothe Keynesian Crossthe Loanable Funds modelthe LM curve, and its relation tothe Theory of Liquidity Preference how the IS-LM model determines income and the interest rate in the short run when P is fixed slide 3IS 曲线，和它与曲线，和它与的关系的关系凯恩斯交叉图凯恩斯交叉图可贷

2、资金模型可贷资金模型LM 曲线，和它与曲线，和它与的关系的关系流动性偏好理论流动性偏好理论当物价水平当物价水平P 固定不变时，固定不变时，IS-LM 模型模型如何决定短期中的收入和利率如何决定短期中的收入和利率slide 4Chapter 9 introduced the model of aggregate demand and aggregate supply. Long run prices flexible output determined by factors of production & technology unemployment equals its natura

3、l rateShort run prices fixed output determined by aggregate demand unemployment is negatively related to outputslide 5第第 9 章介绍了总需求与总供给模型章介绍了总需求与总供给模型长期长期 价格具有伸缩性价格具有伸缩性 产出取决于生产要素和技术水平产出取决于生产要素和技术水平 失业率等于自然失业率失业率等于自然失业率短期短期 价格固定不变价格固定不变 产出取决于总需求产出取决于总需求 失业率与产出呈负相关失业率与产出呈负相关slide 6 This chapter develo

4、ps the IS-LM model, the theory that yields the aggregate demand curve. We focus on the short run and assume the price level is fixed. slide 7 本章开发本章开发IS-LM 模型，获得总需求曲线模型，获得总需求曲线的理论的理论 我们集中于短期，并且假设价格水平是我们集中于短期，并且假设价格水平是固定的固定的slide 8A simple closed economy model in which income is determined by expendi

5、ture. (due to J.M. Keynes)Notation: I = planned investmentPE = C + I + G = planned expenditureY = real GDP = actual expenditureDifference between actual & planned expenditure: unplanned inventory investmentslide 9一个简单的封闭经济模型，其中收入由支出决一个简单的封闭经济模型，其中收入由支出决定定(归功于约翰归功于约翰.梅纳德梅纳德.凯恩斯凯恩斯)符号符号: I = 计划计划投

6、资投资PE = C + I + G = 计划支出计划支出Y = 实际实际 GDP = 实际支出实际支出实际与计划支出的差别：未计划的存货投资实际与计划支出的差别：未计划的存货投资slide 10()CC YTII,GGTTconsumption function:for now, investment is exogenous:planned expenditure:Equilibrium condition:govt policy variables:slide 11()CC YTII,GGTT消费函数消费函数:对于现在而言，对于现在而言， 投资是外生的投资是外生的:计划支出计划支出:均衡条

7、件均衡条件:政府政策变量政府政策变量:实际支出实际支出计划支出计划支出slide 12income, output, Y PEplannedexpenditurePE =C +I +G MPC1slide 13收入，产出，收入，产出， Y PE计划支出计划支出PE =C +I +G MPC1slide 14income, output, Y PEplannedexpenditurePE =Y 45slide 15收入，产出，收入，产出， Y PE计划支出计划支出PE =Y 45slide 16income, output, Y PEplannedexpenditurePE =Y PE =C +

8、I +G Equilibrium incomeslide 17收入，产出，收入，产出， Y PE计划支出计划支出PE =Y PE =C +I +G 均衡收入均衡收入slide 18Y PEPE =Y PE =C +I +G1PE1 = Y1PE =C +I +G2PE2 = Y2 YAt Y1, there is now an unplanned drop in inventoryso firms increase output, and income rises toward a new equilibrium Gslide 19Y EPE =Y PE =C +I +G1PE1 = Y1PE

9、 =C +I +G2PE2 = Y2 Y在在 Y1, 现在出现存货的现在出现存货的非计划的下非计划的下降降 所以企业提升所以企业提升产出，并且收入产出，并且收入上升并趋向新的上升并趋向新的均衡均衡 Gslide 20YCIGYCIG MPCYG CG (1MPC)YG 11MPCYG equilibrium conditionin changesbecause I exogenousbecause C = MPC Y Collect terms with Y on the left side of the equals sign:Finally, solve for Y :slide 21YC

10、IGYCIG MPCYG CG (1MPC)YG 11MPCYG 均衡条件均衡条件变动量变动量因为因为 I 是外生的是外生的因为因为 C = MPC Y 对对 Y 移项合并移项合并:最后，求出最后，求出 Y :slide 22Example: MPC = 0.8 11MPC11510 80 2.YGGGGThe increase in G causes income to increase by 5 times as much!slide 23例子例子: MPC = 0.8 11MPC11510 80 2.YGGGGG 的增加造成收入增加的增加造成收入增加5倍之多倍之多!slide 24In

11、the example with MPC = 0.8, Definition: the increase in income resulting from a $1 increase in G.In this model, the G multiplier equals11MPCYG1510.8YGslide 25在在MPC = 0.8的例子中，的例子中， 定义定义: 政府购买政府购买G 增加增加1美元会引起收入增加多美元会引起收入增加多少少在本模型中，政府购买乘数在本模型中，政府购买乘数11MPCYG1510.8YGslide 26Initially, the increase in G c

12、auses an equal increase in Y: Y = G.But Y C further Y further C further YSo the final impact on income is much bigger than the initial G.slide 27一开始，一开始， G 的增加引起了的增加引起了Y 的等量增加的等量增加: Y = G.但是但是 Y C 进一步进一步 Y 进一步进一步 C 进一步进一步 Y所以最终对收入的效应比初始的所以最终对收入的效应比初始的 G 大得多大得多slide 28Y EPE =Y PE =C2 +I +GPE2 = Y2PE

13、=C1 +I +GPE1 = Y1 YAt Y1, there is now an unplanned inventory buildupso firms reduce output, and income falls toward a new equilibrium C = MPC TInitially, the tax increase reduces consumption, and therefore PE:slide 29Y EPE =Y PE =C2 +I +GPE2 = Y2PE =C1 +I +GPE1 = Y1 Y在在Y1, 现在出现非计现在出现非计划的存货建立划的存货建立所

14、以企业减少所以企业减少产出，且收入下产出，且收入下降并趋向新的均降并趋向新的均衡衡 C = MPC T一开始，税收的增一开始，税收的增加减少了消费，因加减少了消费，因此此PE:slide 30YCIG MPCYT C (1MPC)MPCYT eqm condition in changesI and G exogenousSolving for Y :MPC1MPCYT Final result:slide 31YCIG MPCYT C (1MPC)MPCYT 变动量的均衡条件变动量的均衡条件I 和和 G 是外生的是外生的求解求解 Y :MPC1MPCYT 最终结果最终结果:slide 32d

15、ef: the change in income resulting from a $1 increase in T :MPC1MPCYT0 80 8410 80 2.YT If MPC = 0.8, then the tax multiplier equalsslide 33定义定义: 1美元税收变动引起的收入变动量美元税收变动引起的收入变动量 :MPC1MPCYT0 80 8410 80 2.YT 若若 MPC = 0.8，那么税收乘数等于，那么税收乘数等于slide 34is negative: A tax hike reduces consumer spending, which re

16、duces income.is greater than one (in absolute value): A change in taxes has a multiplier effect on income. is smaller than the govt spending multiplier: Consumers save the fraction (1-MPC) of a tax cut, so the initial boost in spending from a tax cut is smaller than from an equal increase in G. slid

17、e 35是是 负的负的: 税收增加减少了消费者税收增加减少了消费者支出，从而减少了收入支出，从而减少了收入是是 大于大于1 (绝对值绝对值): 税收的改变对收入也有税收的改变对收入也有乘数效应乘数效应比比 政府购买乘数小政府购买乘数小: 消费者保存消费者保存减少的税收的减少的税收的(1-MPC) 比例，所以来自比例，所以来自减税的消费支出的初始增加比来自等量的政府购买增减税的消费支出的初始增加比来自等量的政府购买增加加 要小要小Cutting taxes to stimulate the economy: The Kennedy and Bush Tax Cuts1964Supplysider

18、s The incentive effects of the cut in income tax rates When workers are allowed to keep a higher fraction of their earnings, they supply substantially more labor and expand the aggregate supply 2001,2003slide 36Increasing Government Purchases to Stimulate the Economy: The Obama Spending Plan a sizab

19、le stimulus package to increase aggregate demand$800 billion,5% of GDPsome tax cut and higher transfer paymentsmuch of it was government purchases of goods and servicesslide 37The government purchases multiplier is 1.57The tax multiplier is only 0.99Other economists are skeptical:infrastructureTake

20、time Not be in demand$787 billion,Feb,17,2009slide 38slide 39Use a graph of the Keynesian Cross to show the impact of an increase in investment on the equilibrium level of income/output. slide 40运用凯恩斯交叉图来说明投资的增运用凯恩斯交叉图来说明投资的增加对收入加对收入/产出的均衡水平的影响产出的均衡水平的影响slide 41def: a graph of all combinations of r

21、and Y that result in goods market equilibrium,i.e. actual expenditure (output) = planned expenditureThe equation for the IS curve is:()( )YC YTI rGslide 42定义定义: 表示导致产品市场均衡的表示导致产品市场均衡的r 和和 Y 的所有的所有组合组合即即 实际支出实际支出 (产出产出) = 计划支出计划支出IS 曲线的方程是：曲线的方程是：()( )YC YTI rGslide 43Y2Y1Y2Y1r IY PErY PE =C +I (r1 )

22、+G PE =C +I (r2 )+G r1r2PE =YIS I E Yslide 44Y2Y1Y2Y1r IY PErY PE =C +I (r1 )+G PE =C +I (r2 )+G r1r2PE =YIS I PE Yslide 45The IS curve is negatively sloped. Intuition:A fall in the interest rate motivates firms to increase investment spending, which drives up total planned spending (PE ). To restor

23、e equilibrium in the goods market, output (a.k.a. actual expenditure, Y ) must increase. slide 46 IS 向右下方倾斜向右下方倾斜直觉直觉:利率的下降刺激企业增加投资支出，使利率的下降刺激企业增加投资支出，使得总计划支出上升得总计划支出上升 (PE ). 为了恢复产品市场的均衡，产出（等于为了恢复产品市场的均衡，产出（等于 实际支出，实际支出， Y ）必须增加）必须增加slide 47S, IrI (r ) r1r2rYY1r1r2(a)The L.F. model(b) The IS curveY

24、2S1S2ISslide 48S, IrI (r ) r1r2rYY1r1r2(a)可贷资金模型可贷资金模型(b) IS 曲线曲线Y2S1S2ISslide 49We can use the IS-LM model to see how fiscal policy (G and T ) can affect aggregate demand and output. Lets start by using the Keynesian Cross to see how fiscal policy shifts the IS curveslide 50使用使用IS-LM 模型来分析财政政策如模型来分

25、析财政政策如何影响总需求和产出何影响总需求和产出 (G 和和 T )让我们首先用凯恩斯交叉图来分析财让我们首先用凯恩斯交叉图来分析财政政策如何移动政政策如何移动IS 曲线曲线slide 51Y2Y1Y2Y1At any value of r, G PE YY PErY PE =C +I (r1 )+G1 PE =C +I (r1 )+G2 r1PE =YIS1The horizontal distance of the IS shift equals IS2so the IS curve shifts to the right.11 MPCYG Yslide 52Y2Y1Y2Y1在在 r的任意

26、值上，的任意值上， G PE YY PErY PE =C +I (r1 )+G1 PE =C +I (r1 )+G2 r1PE =YIS1IS 移动的水平距移动的水平距离等于离等于IS2所以所以IS 曲线向右曲线向右移动移动 11 MPCYG Yslide 53Use the diagram of the Keynesian Cross or Loanable Funds model to show how an increase in taxes shifts the IS curve. slide 54运用凯恩斯交叉图或可贷资金模型来运用凯恩斯交叉图或可贷资金模型来说明税收的增加如何移动说

27、明税收的增加如何移动IS 曲线曲线slide 55due to John Maynard Keynes.A simple theory in which the interest rate is determined by money supply and money demand. slide 56约翰约翰.梅纳德梅纳德.凯恩斯提出凯恩斯提出一个简单的理论：利率取决于货币供一个简单的理论：利率取决于货币供给与货币需求给与货币需求slide 57The supply of real money balances is fixed:sM PM PM/P real money balancesri

28、nterestratesM PM Pslide 58实际货币余额实际货币余额的供给是固定的供给是固定的的:sM PM PM/P 实际货币余额实际货币余额r利率利率sM PM Pslide 59Demand forreal money balances:M/P real money balancesrinterestratesM PM P( )dM PL rL (r ) slide 60实际货币余额实际货币余额的需求的需求:M/P 实际货币余额实际货币余额r利率利率sM PM P( )dM PL rL (r ) slide 61The interest rate adjusts to equat

29、e the supply and demand for money:M/P real money balancesrinterestratesM PM P( )M PL rL (r ) r1slide 62利率调整使利率调整使得货币的供得货币的供给和需求相给和需求相等：等：M/P 实际货币余额实际货币余额r利率利率sM PM P( )M PL rL (r ) r1slide 63To increase r, Fed reduces MM/P real money balancesrinterestrate1MPL (r ) r1r22MPslide 64为了提高为了提高r， 联联储减少储减少M

30、M/P 实际货币余额实际货币余额r利率利率1MPL (r ) r1r22MPslide 65Late 1970s: 10%Oct 1979: Fed Chairman Paul Volcker announced that monetary policy would aim to reduce inflation.Aug 1979-April 1980: Fed reduces M/P 8.0%Jan 1983: = 3.7%slide 661970年代末期年代末期: 10%1979年年10月月: 联储主席保罗联储主席保罗. 沃尔克宣布了沃尔克宣布了旨在降低通货膨胀的货币政策旨在降低通货膨胀的

31、货币政策1979年年8月月-1980年年4月月: 联储减少联储减少M/P 8.0%1983年年1月月: = 3.7%slide 67i 01/1983: i = 8.2%8/1979: i = 10.4%4/1980: i = 15.8%flexiblestickyQuantity Theory, Fisher Effect(Classical)Liquidity Preference(Keynesian)predictionactual outcomeThe effects of a monetary tightening on nominal interest ratespricesmod

32、ellong runshort runslide 68i 01/1983: i = 8.2%8/1979: i = 10.4%4/1980: i = 15.8%有伸缩性的有伸缩性的黏性黏性数量论，费雪效应数量论，费雪效应(古典的古典的)流动性偏好流动性偏好(凯恩斯主义凯恩斯主义)预测预测实际产出实际产出货币紧缩对名义利率的影响货币紧缩对名义利率的影响价格价格模型模型长期长期短期短期slide 69Now lets put Y back into the money demand function:( ,)M PL r YThe LM curve is a graph of all combin

33、ations of r and Y that equate the supply and demand for real money balances.The equation for the LM curve is:dM PL r Y( ,)slide 70现在让我们把现在让我们把Y 放回货币需求函数放回货币需求函数:( ,)M PL r YLM 曲线曲线 表示使得实际货币余额的供给和需求相表示使得实际货币余额的供给和需求相等的所有等的所有r 和和 Y 的组合的组合:dM PL r Y( ,)slide 71M/P r1MPL (r , Y1 ) r1r2rYY1r1L (r , Y2 )

34、r2Y2LM(a) Real money balance market(b) LM Curveslide 72M/P r1MPL (r , Y1 ) r1r2rYY1r1L (r , Y2 ) r2Y2LM(a)实际货币余额市场实际货币余额市场(b) LM 曲线曲线slide 73The LM curve is positively sloped. Intuition:An increase in income raises money demand. Since the supply of real balances is fixed, there is now excess demand

35、in the money market at the initial interest rate. The interest rate must rise to restore equilibrium in the money market.slide 74LM 曲线的斜率为正曲线的斜率为正直觉直觉:收入的增加提高了货币需求。收入的增加提高了货币需求。由于实际余额的供给是固定的，现在在初始由于实际余额的供给是固定的，现在在初始利率上，货币市场上存在过量的需求利率上，货币市场上存在过量的需求利率必须提高以恢复货币市场的均衡利率必须提高以恢复货币市场的均衡slide 75M/P r1MPL (r

36、, Y1 ) r1r2rYY1r1r2LM1(a)The market for real money balances(b) The LM curve2MPLM2slide 76M/P r1MPL (r , Y1 ) r1r2rYY1r1r2LM1(a)实际货币余额市场实际货币余额市场(b) LM 曲线曲线2MPLM2slide 77Suppose a wave of credit card fraud causes consumers to use cash more frequently in transactions. Use the Liquidity Preference model

37、 to show how these events shift the LM curve. slide 78假设信用卡欺诈造成了消费者在交易中假设信用卡欺诈造成了消费者在交易中更频繁地使用现金更频繁地使用现金运用流动偏好模型来说明这些事件如何运用流动偏好模型来说明这些事件如何移动移动LM 曲线曲线 slide 79The short-run equilibrium is the combination of r and Y that simultaneously satisfies the equilibrium conditions in the goods & money mark

38、ets: ()( )YC YTI rGY r( ,)M PL r YISLMEquilibriuminterestrateEquilibriumlevel ofincomeslide 80短期均衡是同时满足产品短期均衡是同时满足产品与货币市场均衡条件的与货币市场均衡条件的 r 和和 Y 的组合的组合: ()( )YC YTI rGY r( ,)M PL r YISLM均衡利率均衡利率收入的均衡收入的均衡水平水平slide 81KeynesianCrossTheory of Liquidity PreferenceIScurveLM curveIS-LMmodelAgg. demandcurve

39、Agg. supplycurveModel of Agg. Demand and Agg. SupplyExplanation of short-run fluctuationsslide 82凯恩斯交凯恩斯交叉图叉图流动偏好理流动偏好理论论IS曲线曲线LM 曲曲线线IS-LM模型模型总需求总需求曲线曲线总供给总供给曲线曲线总需求与总需求与总供给模总供给模型型解释短期波解释短期波动动slide 831.Keynesian Crossbasic model of income determinationtakes fiscal policy & investment as exogeno

40、usfiscal policy has a multiplied impact on income.2. IS curvecomes from Keynesian Cross when planned investment depends negatively on interest rateshows all combinations of r and Y that equate planned expenditure with actual expenditure on goods & servicesslide 841.凯恩斯交叉图凯恩斯交叉图基本的收入决定模型基本的收入决定模型把财政政策和计划投资作为外生的把财政政策和计划投资作为外生的财政政策对收入有乘数效应财政政策对收入有乘数效应2. IS 曲线曲线来自于凯恩斯交叉图，当计划投资负向取决来自于凯恩斯交叉图，当计划投资负向取决于利率时于利率时表示了使得产品与服务的计划支出与实际支表示了使得产品与服务的计划支出与实际支出相等的所有出相等的所有r 和和 Y 的组