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1、巴罗宏观经济学：现代观巴罗宏观经济学：现代观点第点第8 8章章Cyclical Behavior of Real GDPRecessions and BoomsReal GDP =trend real GDP+cyclical part of real GDPCyclical part of real GDP lComing from the business cycle lShort-term economic fluctuations.2Macroeconomics Chapter 8 An Equilibrium Business-Cycle ModelThe ModellY=A F(K
2、,L)the capital stock,K,as fixed in the short run,the labor input,L,is fixed.lChanges in Y will reflect only changes in A.When A rises,Y rises,When A falls,Y falls.9Macroeconomics Chapter 8 An Equilibrium Business-Cycle ModelThe ModellThe marginal product of labor and the real wage rateAn increase in
3、 the technology level,A,raises the marginal product of labor,MPL,for given inputs of capital,K,and labor,L.10Macroeconomics Chapter 8 An Equilibrium Business-Cycle Model11Macroeconomics Chapter 8 An Equilibrium Business-Cycle Model12Macroeconomics Chapter 8 An Equilibrium Business-Cycle ModelThe Mod
4、ellMarginal product of capital,real rental price,and the interest rateAn increase in the technology level,A,raises the marginal product of capital,MPK,for given inputs of capital,K,and labor,L13Macroeconomics Chapter 8 An Equilibrium Business-Cycle Model14Macroeconomics Chapter 8 An Equilibrium Busi
5、ness-Cycle Model15Macroeconomics Chapter 8 An Equilibrium Business-Cycle ModellMarginal product of capital,real rental price,and the interest ratei=R/P i=MPK(evaluated at given K and L)lThe model predicts that an economic boom will have a relatively high interest rate,whereas a recession will have a
6、 relatively low interest rate.16Macroeconomics Chapter 8 An Equilibrium Business-Cycle ModelConsumption,saving,and investmentlAggregate household budget constraint Given the markets for bonds,labor,and capital services clear:lC+K=Y K17Macroeconomics Chapter 8 An Equilibrium Business-Cycle ModelC+K=A
7、 F(K,L)Kldepreciation,K,is fixed in the short run,lAn increase in A raises real GDP for given K and L,we see that a rise in A raises overall real income.18Macroeconomics Chapter 8 An Equilibrium Business-Cycle ModelConsumption,saving,and investmentlincome effect：The increase in real income motivates
8、 households to raise current consumption and future consumption.lIntertemporal-substitution effect：The increase in the interest rate tends to reduce current consumption.lThe net change depends on whether the income effect is stronger or weaker than the intertemporal-substitution effect.19Macroeconom
9、ics Chapter 8 An Equilibrium Business-Cycle ModelConsumption,saving,and investmentlAssume that the change in A is permanent.the increases in real income tend also to be permanent.lThe propensity to consume out of higher income would be close to one.lWhen the increase in A is permanent,current consum
10、ption will rise.However,as long as the intertemporal-substitution operates at all,the increase in current consumption will be less than the increase in real GDP.20Macroeconomics Chapter 8 An Equilibrium Business-Cycle ModelConsumption,saving,and investmentlSince current consumption,C,rises,but by le
11、ss than the increase in real GDP,Y.Therefore,net investment,K,must increase-the increase in real GDP shows up partly as more C and partly as more K.lSince net investment,K,equals real saving,this result is consistent with our finding that real saving increased.21Macroeconomics Chapter 8 Matching the
12、 Theory with the FactsConsumption and InvestmentlWhen a variable fluctuates in the same direction as real GDP that variable is procyclical.A procyclical variable moves in the same direction as the business cycleit tends to be high relative to its trend in a boom and low relative to its trend in a re
13、cession.22Macroeconomics Chapter 8 Matching the Theory with the FactsConsumption and InvestmentlA variable that fluctuates in the opposite direction from real GDP is countercyclical.lOne that has little tendency to move in a particular direction during a business cycle is acyclical.23Macroeconomics
14、Chapter 8 Matching the Theory with the Facts24Macroeconomics Chapter 8 Matching the Theory with the Facts25Macroeconomics Chapter 8 Matching the Theory with the FactsConsumption and InvestmentlPermanent shifts in the technology level,A,match up with some of the empirical patterns Increases in A gene
15、rate economic booms,where real GDP increases,consumption and investment increases.Decreases in A create recessions,where real GDP,consumption,and investment all decline.26Macroeconomics Chapter 8 Matching the Theory with the FactsThe Real Wage RatelThe model predicts that the real wage rate,w/P,will
16、 be relatively high in booms and relatively low in recessions.27Macroeconomics Chapter 8 Matching the Theory with the Facts28Macroeconomics Chapter 8 Matching the Theory with the FactsThe Real Rental PricelThe model predicts that the real rental price of capital,R/P,will be relatively high in booms
17、and relatively low in recessions.29Macroeconomics Chapter 8 Matching the Theory with the Facts30Macroeconomics Chapter 8 Matching the Theory with the FactsThe Interest RatelThe model predicts that booms will have a high interest rate,i,whereas recessions will have a low interest rate.31Macroeconomic
18、s Chapter 8 Temporary Changes in the Technology LevelA decrease in A due to a harvest failure or a general strike would be temporary.To allow for these cases,we now assume that the change in A is temporary.32Macroeconomics Chapter 8 Temporary Changes in the Technology LevelIf A increases temporarily
19、,real GDP,A F(K,L),still rises for fixed values of K and L.The marginal product of capital,MPK,and the interest rate,i,also rise as before.The intertemporal-substitution effect from the higher i still motivates households to reduce current consumption,C,and raise current real saving.33Macroeconomics
20、 Chapter 8 Temporary Changes in the Technology LevelThe model therefore predicts that economic boom would feature high real GDP and investment.lConsumption would rise by a small amount.A recession would have low real GDP and investment.lConsumption would decline by a modest amount.34Macroeconomics C
21、hapter 8 Variations in Labor InputLabor SupplylMore labor supplied means less leisure time for the family.lAssume that households also like more leisure time.lAs with consumption and saving,the choice of Ls involves substitution and income effects.35Macroeconomics Chapter 8 Variations in Labor Input
22、The substitution effect for leisure and consumptionlIf the household chooses to work one more hour and thereby have one less hour of leisure,the extra w/P of real wage income pays for w/P more units of consumption.lTherefore,the household can substitute one less hour of leisure for w/P more units of
23、 consumption.36Macroeconomics Chapter 8 Variations in Labor InputThe substitution effect for leisure and consumptionlIf w/P rises,the household gets a better deal by working more because it gets more consumption for each extra hour worked.Since the deal is better,we predict that the household respon
24、ds to a higher w/P by working more.37Macroeconomics Chapter 8 Variations in Labor InputThe substitution effect for leisure and consumptionlA higher real wage rate,w/P,raises the quantity of labor supplied,Ls38Macroeconomics Chapter 8 Variations in Labor InputIncome effects on labor supplylA higher w
25、/P means higher real wage income,(w/P)Ls lHousehold spends the extra income on consumption and leisure time.lA higher w/P leads to a smaller quantity of labor supplied,Ls.39Macroeconomics Chapter 8 Variations in Labor InputIncome effects on labor supplylResolve the ambiguity by considering whether t
26、he income effect is strong or weaklC1+C2/(1+i1)+C3/(1+i1)(1+i2)+=(1+i0)(B0/P+K0)+(w/P)1Ls1+(w/P)2Ls2/(1+i1)+(w/P)3Ls3/(1+i1)(1+i2)+40Macroeconomics Chapter 8 Variations in Labor InputIncome effects on labor supplylA permanent increase in real wage rates results in a large income effect.lIf the chang
27、e in year 1s real wage rate,(w/P)1,is temporary,the income effect is small.lThe income effect will be weaker than the substitution effect.41Macroeconomics Chapter 8 Variations in Labor InputIntertemporal-substitution effects on labor supplylC1+C2/(1+i1)+C3/(1+i1)(1+i2)+=(1+i0)(B0/P+K0)+(w/P)1Ls1+(w/
28、P)2Ls2/(1+i1)+(w/P)3Ls3/(1+i1)(1+i2)+42Macroeconomics Chapter 8 Variations in Labor InputIntertemporal-substitution effects on labor supply.lIf the interest rate,i1,rises,a unit of year2s real wage income,(w/P)2Ls2,becomes less valuable as a present value compared to a unit of year1s real wage incom
29、e,(w/P)1Ls 1.lWe therefore predict that the household would increase Ls1 and decrease Ls2 as the interest rate increases.43Macroeconomics Chapter 8 Variations in Labor Input44Macroeconomics Chapter 8 Variations in Labor InputFluctuations in Labor InputlMeasures of labor input are procyclical:they mo
30、ve in the same direction as real GDP during booms and recessions.EmploymentTotal hours worked45Macroeconomics Chapter 8 Variations in Labor Input46Macroeconomics Chapter 8 Variations in Labor InputThe cyclical behavior of labor input:theorylIncrease in A will lead to:The real wage rate increasesLabo
31、r inputs increase.47Macroeconomics Chapter 8 Variations in Labor Input48Macroeconomics Chapter 8 Variations in Labor InputThe cyclical behavior of labor productivitylMeasures of labor productivity,Y/L,is real GDP per worker,Real GDP per worker-hour.Labor productivity turns out to be procyclical in b
32、oth cases.49Macroeconomics Chapter 8 Extra：labor supply modelFor simplicity:the household has only one member and he lives only for one period and has no initial wealth.FOC:50Macroeconomics Chapter 8 Extra：labor supply modelIntuition:In one period,the income and substitution effects of a change in the wage offset each other.51Macroeconomics Chapter 8 Extra：labor supply model Two periods:FOC:52Macroeconomics Chapter 8 Extra：labor supply model Intuition:intertemporal substitution in labor supply53Macroeconomics Chapter 8 结束语结束语谢谢大家聆听！谢谢大家聆听！54