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1、第六章扩大的凯恩斯模型本讲稿第一页，共五十九页Government Expenditures:本讲稿第二页，共五十九页Government Expenditures:Account for almost 20 percent of total aggregate expenditures.the Keynesian model assumes G to be autonomous so that G simply equals autonomous government expenditures G0.As with the investment function,the government
2、 expenditure function can be graphically portrayed as a horizontal line.本讲稿第三页，共五十九页Government Expenditures:In general,government expenditures are less volatile易发生变动的 than investment(although episodic events系列事件 such as wars and natural disasters can lead to large fluctuations).本讲稿第四页，共五十九页均衡所得决定为简化
3、分析，我们将政府财产与转移所得、补贴以及转移性支出等合并到政府税收内，求得一个税收净额，并由政府决定，不随意变动；政府投资与家庭、企业投资向合并，仍为外生变量。（G、T本来与Y相关）本讲稿第五页，共五十九页本讲稿第六页，共五十九页与简单凯恩斯模型相比：乘数没有变化自发性支出发生了变化，多出了G0与T0G0与T0对自发性支出的影响程度不同，可以由他们之前的符号看出。他们对Y的影响程度也不同。税收占自发性支出的项目不是T0而是cT0(为什么？)T0对自发性消费支出的增加产生反作用，并且，为cT0，政府税收净额T0对总需求的影响是间接通过可支配所得的变动产生的，对自发性消费支出的作用为cT0，其余的
4、(1-c)T0被民间减少储蓄的方式吸收。本讲稿第七页，共五十九页Y0Y1Y*0C=Ca+c(Y-T0)C+I=Ca+c(Y-T0)+I0C+I+G=Ca+c(Y-T0)+I0+G0Ca-cT0+I0+G0Ca-cT0+I0Ca-cT0E本讲稿第八页，共五十九页开放经济条件下的均衡收入决定进出口需求的决定出口需求决定、外国居民收入水平、本国产品相对价格、本国一般价格水平、汇率、出口退税、补贴政策等进口需求决定因素本国居民收入水平、进口品与本国产品比价、汇率及进口管制政策等边际进口倾向（MPI）与平均进口倾向(API)MPI为增加一单位所得（本国）所增加的进口数额。API为平均每单位所的中用于进口
5、产品的比例。本讲稿第九页，共五十九页Net Exports本讲稿第十页，共五十九页本讲稿第十一页，共五十九页本讲稿第十二页，共五十九页Net ExportsBecause exports create domestic production,income,and employment for an economy,they must be added to aggregate expenditures.However,when we purchase imports from a foreign country,no such production,income,or employment i
6、s created so that imports must be subtracted from aggregate expenditures.本讲稿第十三页，共五十九页CanadaCanadaFranceFranceGermanyGermanyItalyItalyJapanJapanUnited KingdomUnited KingdomUnited StatesUnited StatesPositive Net ExportsPositive Net ExportsNegative Net ExportsNegative Net Exports-180180-140140-100100-
7、60-60-20-20-0-020206060100100Billions of dollarsBillions of dollars本讲稿第十四页，共五十九页开放经济条件下的均衡所得决定本讲稿第十五页，共五十九页比较此式与封闭经济条件下的收入决定，不仅自发性支出多出了，即出口与进口之差额，乘数也由1/1-c降低为1/1-c+m，即边际储蓄倾向与边际进口倾向之和的导数。乘数之所以缩小，是因为在开放经济条件下，当所得增加一单位时，虽然使诱发性支出增加c单位，但其中的m单位所购买的是进口品，因此对本国国民产出的购买仅有c-m单位，此时，乘数作用也由封闭经济中的1/1-c变为开放经济中的1/1-c+
8、m。两点说明：上述模型是极度简化的凯恩斯模型，实际经济过程比这些模型复杂的多。上述推论的前提是价格水平不变，影响支出的因素除了所得之外，其他因素的影响没有给与考虑，如利率、对未来的预期、流动性资产的数量等。上述分析所得到的乘数，除了比更完整的模型所求得的有所差异外，乘数效果的充分发挥也须假以相当时日。本讲稿第十六页，共五十九页C+I+G=Ca+c(Y-T0)+I0+G0C+I+G+X-M=Ca+c(Y-T0)+I0+G0+X0-(Ma+mY)Y0Y*Ca-cT0+I0+G0+X0-MaCa-cT0+I0+G0本讲稿第十七页，共五十九页紧缩缺口、膨胀缺口与经济波动紧缩缺口（Deflationar
9、y Gap）与膨胀缺口(Inflationary Gap)为了达成充分就业，总需求必须增加的数量，称为紧缩缺口。或者说，紧缩缺口是自发性支出低于为维持充分就业所必需的水平的数量。为避免因需求过多引起物价膨胀所必须减少的总需求的数量，为膨胀缺口。本讲稿第十八页，共五十九页AD1ADfAD2Y1YfY2P0P1AE1AEfAE2总需求e1efe2E1EfE2紧缩缺口膨胀缺口本讲稿第十九页，共五十九页周期波动时间GDP扩张顶峰衰退谷低本讲稿第二十页，共五十九页周期波动的原因外部因素与内部因素在总支出各项目中，波动较大的主要是投资、政府消费与净出口。投资的不稳定性诱发性投资（Induced Inves
10、tment）与加速原理诱发性投资是指因国民所得增加而诱发的投资。用边际投资倾向(Marginal Propensity to Invest,MPI)衡量。所谓边际投资倾向是指国民所得增加一单位引起的投资增加量。I=Ia+iY简单凯恩斯模型中的收入决定变为：本讲稿第二十一页，共五十九页此时的自发性支出乘数为1/（1-c-i），高于投资完全是自发性投资时的乘数1/（1-c）。诱发性投资的存在，有加强乘数效果的作用，也扩大了任何外在因素对自发性支出冲击所引起的经济波动。本讲稿第二十二页，共五十九页加速原理导致投资不稳定的因素还有加速原理基本假设：1、现有资本设备都充分利用；2、为生产一单位产品，理想
11、的资本设备使用量不变，因此，理想的资本设备数量与国民产出间有一固定的比例关系，此比例称为资本产出比（Capital/output Ratio），且数值大于1，用v表示。理想的资本存量与国民生产Y之间的关系为：Kt+1=vYt假设生产者认为第t期的产出Yt在Yt+1期仍将维持，因此打算在t+1期以vYt的理想资本量生产。由于现有资本设备都以充分利用，因此国民生产变动将引起资本量做v倍调整Kt+1-K1=v(Yt-Yt-1)=It本讲稿第二十三页，共五十九页上述公式表明，投资净额为国民所得变化量，乘以资本/产出比，因v是一个大于1的数，因此，投资是所得变动量的函数，而且是一个倍数的函数关系，这一倍
12、数称为加速度。加速原理说明的是，国民所得变动量对投资净额需求的加速度影响。加速度是指资本产出比，通常大于1。乘数乘数加速原理加速原理加速原理探讨的的是所得变动对投资的影响，而乘数原理探讨的是需求（包括投资）变动对所得增加的影响。二者结合在一起，构成乘数加速原理。自发性投资增加（总需求增加）乘数效果的所得增加加速效果的投资增加乘数效果的所得增加自发性投资减少（总需求减少）乘数效果的所得减少加速效果的投资减少乘数效果的所得减少本讲稿第二十四页，共五十九页Closing a Recessionary GapExpansionary fiscal policy can be used to close
13、 the recessionary gap.Before we can demonstrate this,weve got one more concept to master the so-called“Keynesian expenditure multiplier”.本讲稿第二十五页，共五十九页The Keynesian MultiplierThe Keynesian expenditure multiplier is the number by which a change in aggregate expenditures must be multiplied in order to
14、 determine the resulting change in total output.This multiplier is greater than one and the reason is that income is respent-not just once but many times after the initial increase.本讲稿第二十六页，共五十九页Calculating the MultiplierIn the Keynesian model,the multiplier is simply the reciprocal of the MPS(or on
15、e divided by one minus the MPC).MPCMPCMultiplierMultiplier0.90.9?0.80.8?0.750.75?0.50.5?本讲稿第二十七页，共五十九页1001005050MPC=0.5MPC=0.5252512.512.56.256.25Multiplier=1/(1-0.5)=2Multiplier=1/(1-0.5)=21001007575MPC=0.75MPC=0.7556.2556.2542.1942.1931.6431.64Multiplier=1/(1-0.75)=4Multiplier=1/(1-0.75)=410010080
16、80MPC=0.8MPC=0.8646451.251.240.9640.96Multiplier=1/(1-0.8)=5Multiplier=1/(1-0.8)=51001009090MPC=0.9MPC=0.9818172.972.965.6165.61Multiplier=1/(1-0.9)=10Multiplier=1/(1-0.9)=10本讲稿第二十八页，共五十九页How the Multiplier WorksSuppose,then,that the U.S.permanently increases defense spending by$100 billion in respo
17、nse to a threat to the oil fields in the Mideast.What will be the effect of this increase in G on the GDP?本讲稿第二十九页，共五十九页How the Multiplier Works 3,6003,600 3,9003,900C+I+GC+I+GC+I+GC+I+GE EEETotal Spending(billions of dollars)Total Spending(billions of dollars)Gross domestic product(billions of doll
18、ars)Gross domestic product(billions of dollars)GDPGDP4545o o$100$100本讲稿第三十页，共五十九页Closing a Recessionary GapIt should also be clear how important the role of the multiplier is in the conduct of fiscal policy.本讲稿第三十一页，共五十九页A Recessionary GapAPAPAggregate ExpendituresAggregate ExpendituresIncomeIncomeA
19、E=C+I GAE=C+I G900900800800Recessionary GapRecessionary GapMPC=0.8MPC=0.8本讲稿第三十二页，共五十九页A Recessionary GapAPAPAggregate ExpendituresAggregate ExpendituresIncomeIncomeAE=C+I GAE=C+I G900900800800Recessionary GapRecessionary GapMPC=0.8MPC=0.8本讲稿第三十三页，共五十九页Tax Cuts as Fiscal Policy Alternatively,we can
20、cut taxes to close this Alternatively,we can cut taxes to close this same$100B recessionary gap(like the same$100B recessionary gap(like the Kennedy tax cut of 1964).Kennedy tax cut of 1964).However,the calculation for the However,the calculation for the appropriate size of the tax cut is more appro
21、priate size of the tax cut is more complicated than for government complicated than for government expenditures.expenditures.本讲稿第三十四页，共五十九页Why?This is because a dollars worth of tax cuts has slightly less of an expansionary effect than a dollars increase in government expenditures.The reason is that
22、 consumers will not increase their expenditures by the full amount of the tax cut.Instead,they will save a portion of that tax cut based on their marginal propensity to save.本讲稿第三十五页，共五十九页First round First round of spendingof spendingSecond Second round of round of spendingspendingThird round Third
23、round of spendingof spendingMore saving=MPS*tax More saving=MPS*tax cutcutMore savingMore savingMore savingMore savingCumulative change in Cumulative change in saving=tax cutsaving=tax cutMore consumption More consumption=MPC*tax cut=MPC*tax cutMore incomeMore incomeMore consumptionMore consumptionM
24、ore incomeMore incomeMore consumptionMore consumptionKeynesian tax multiplier=expenditure multiplier*MPC=c/1-cKeynesian tax multiplier=expenditure multiplier*MPC=c/1-cTax CutTax Cut本讲稿第三十六页，共五十九页An ExampleHow much,then,should taxes be cut to close a$100B recessionary gap assuming the MPC still equal
25、s.8 and the multiplier is 5?本讲稿第三十七页，共五十九页The AnswerAnswer:$25B,or$5B more than we needed to increase G to achieve the same result.We first multiply the expenditure multiplier of 5 times the MPC,yielding a tax multiplier of 4.4 times the$25 billion tax cut yields a$100 billion expansion.本讲稿第三十八页，共五十
26、九页平衡预算乘数政府支出增加完全依靠税收增加给予弥补，而不通过举债实现。当政府支出与税收净额做同额度同方向变动时，预算余额不受影响，此种调整对均衡所得产生的乘数效果，称为平衡预算乘数。在封闭经济简单凯恩斯模型中，平衡预算乘数等于1本讲稿第三十九页，共五十九页Closing An Inflationary GapWe know how to use expansionary fiscal policy to close a recessionary gap.Suppose we face an inflationary gap instead-a gap such as the one in t
27、he late 1960s caused by demand-pull inflation from the Vietnam War and Great Society expenditures.本讲稿第四十页，共五十九页An Inflationary Gap$60B Inflationary Gap$60B Inflationary GapA960960APAPAggregate ExpendituresAggregate ExpendituresGDPGDPAE=C+I GAE=C+I GSlope=.75Slope=.75900900Potential Potential GDPGDPH
28、ow might fiscal policy be How might fiscal policy be used to close the inflationary used to close the inflationary gap?gap?本讲稿第四十一页，共五十九页An Inflationary Gap$60B Inflationary Gap$60B Inflationary GapA960960900900APAPAggregate ExpendituresAggregate ExpendituresGDPGDPAE=C+I GAE=C+I GSlope=.75Slope=.75P
29、otential Potential GDPGDPThe multiplier is four.The multiplier is four.To close this inflationary gap,we To close this inflationary gap,we simply have to reduce government simply have to reduce government expenditures by$15 billion or,expenditures by$15 billion or,alternatively,raise taxes by$20 alt
30、ernatively,raise taxes by$20 billion.billion.At a multiplier of four,either At a multiplier of four,either fiscal policy tool will lead to the fiscal policy tool will lead to the desired economic contraction of desired economic contraction of$60 billion.$60 billion.本讲稿第四十二页，共五十九页Built-In Stabilizers
31、自动稳定器随着收入变化而变化的税收制度失业保险制度（转移支付）诱发性租税随着收入提高，租税收入也提高的税制，称为诱发性租税。固定比例的所得税制度：T=Ta+tY，Yd=Y-Ta-tY=(1-t)Y-Ta 如果所得税率是累进性的，这种自动稳定功能更大本讲稿第四十三页，共五十九页Policy OptionsIs it preferable to increase government spending or cut taxes to eliminate recessionary and inflationary gaps?The answer depends on ones view of the
32、 appropriate size of the government than pure economics.本讲稿第四十四页，共五十九页Liberals Vs.ConservativesLiberals who think that there are many unmet social and infrastructure needs usually recommended increased government spending during recessions and tax increases to fight demand-pull inflation.These actio
33、ns either expand or preserve the absolute size of government.On the other hand,there are conservatives who seek to shrink the size of government.What fiscal policies do you think they will advocate to fight recessions or inflation?本讲稿第四十五页，共五十九页Conservatives PolicyConservatives will generally favor
34、tax cuts during recessions and cuts in government spending to fight demand-pull inflation.本讲稿第四十六页，共五十九页Explaining the Great DepressionIn 1929,the economy was booming and at full employment,but the stock market crash sent the business community into a panic.Businesses cut back sharply on investment
35、and production while frightened consumers cut back dramatically on consumption.本讲稿第四十七页，共五十九页Together,the reactions of business and consumers led to a sharp and sudden downward shift of the aggregate expenditures curve.Business people,in turn responded by decreasing output further.This depressed inc
36、ome and consumption,the economy continued its downward spiral,and eventually unemployment reached a staggering 25 percent of the workforce本讲稿第四十八页，共五十九页With the economy in this depressed state,businesses became unwilling to invest no matter how low interest rates fell.The government stepped in with
37、a massive dose大剂量 of expansionary fiscal policy.The public works projects of Franklin Delano Roosevelts New Deal followed by the dramatic spurt迸发 of defense expenditures for World War II triggered both increased consumption and investment and the economy roared back to full employment.Fiscal Policy
38、to the Rescue本讲稿第四十九页，共五十九页Mechanistic KeynesianismThe Keynesian model provides a very mechanistic approach to curing the economy of a recession.If you know what the actual GDP and full employment GDP are,you know the size of the recessionary or inflationary gap.If you know the MPC and therefore the
39、 multiplier,you know how much to increase or decrease G or T to close the gap.本讲稿第五十页，共五十九页Its Not This Simple If only life were this simple,none of us If only life were this simple,none of us would have to worry about ever being would have to worry about ever being unemployed again and any of us,af
40、ter unemployed again and any of us,after mastering todays simple lesson,would be mastering todays simple lesson,would be qualified to serve as the Presidents top qualified to serve as the Presidents top economic advisor.economic advisor.But such is not the case even if many But such is not the case
41、even if many economists at the height of the 1960s economists at the height of the 1960s Keynesian era thought it was.Keynesian era thought it was.本讲稿第五十一页，共五十九页Crowding OutRefers to the reduction in private sector investment that can be caused by increased government spending,and it can happen when
42、 the government borrows money to finance these expenditures.Such borrowing or“deficit spending”can drive up interest rates.Higher interest rates can,in turn,reduce private sector investment.本讲稿第五十二页，共五十九页Not A Complete ModelA much broader problem with the mechanistic Keynesian approach is that it re
43、lies on a model that is not a complete model of the economy,particularly with respect to the monetary and financial sector.本讲稿第五十三页，共五十九页KeynesianKeynesian Range RangeAggregate OutputThree Ranges of the EconomyIntermediateIntermediate Range RangeClassicalClassical Range RangePricePriceLevelLevel本讲稿第
44、五十四页，共五十九页A Powerful ToolThe second situation where the Keynesian model is useful analytically is for illustrating how a small imbalance between leakages and injections can multiply into a much larger unemployment or inflation problem.本讲稿第五十五页，共五十九页Its WeaknessThe Keynesian model does assume away in
45、flation.It neglects the crucial influence of monetary factors on interest rates and interest-sensitive components of output such as investment.本讲稿第五十六页，共五十九页The Strength Of The AD/AS ModelThe Aggregate Supply-Aggregate Demand model illustrates both price levels and real output.What is the relationsh
46、ip between the Keynesian aggregate expenditures-aggregate production model and the Classical aggregate supply-aggregate demand model?本讲稿第五十七页，共五十九页E EQQADADADADASASASASReal GDPReal GDPPrice LevelPrice LevelPotential Potential GDPGDPQQP PRecessionary Recessionary GapGapReal GDPReal GDPPotential Poten
47、tial GDPGDPTotal spendingTotal spendingC+I+GC+I+GC+I+GC+I+GQQP P4545本讲稿第五十八页，共五十九页ADADADADASASASASE EReal GDPReal GDPPrice LevelPrice LevelPotential Potential GDPGDPQQP PQQE EQQRecessionary Recessionary GapGapReal GDPReal GDPPotential Potential GDPGDPTotal spendingTotal spendingC+I+GC+I+GC+I+GC+I+GQQP P4545本讲稿第五十九页，共五十九页