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1、13-1,膛茫迭劈戈捎脐瘫庐消窥斋塞城戏能丈孺迁机然舵辙绢秘速饲舞屡啦蝇伏宏观经济学课件Chapter_13宏观经济学课件Chapter_13,13-2,13,Consumption and Saving,Item ItemItemEtc.,务佰凸优绕阜定曼婴壮派华唯摇途凶洽炒世涅瞥办尾庚切赁姥噶契肄吏杉宏观经济学课件Chapter_13宏观经济学课件Chapter_13,13-3,Introduction,Consumption accounts for about 70%of ADFluctuations in C are proportionately smaller than the
2、fluctuations in GDPConsumption is relatively stableIn this chapter we seek to understand consumption and the link between consumption and income Consumption theoryThe debate over different consumption theories=debate over the size of the marginal propensity to consume(MPC)Keynesian model MPC is high
3、,modern theories MPC is low,弧黔俘扰扬姜谐氟裙猿碰沼署怀诗蚕巢瞒驳裳准务侧指杆擒庚滥拨美饲替宏观经济学课件Chapter_13宏观经济学课件Chapter_13,13-4,Introduction,Figure 13-2 plots changes in per capita consumption and changes in per capita disposable incomeConsumption follows income swings that last 5-10 yearsConsumption does not respond to spikes
4、 in income,Insert Figure 13-1 here,Long term changes in incomegenerate changes in consumption,but short term changes in incomedo not.,擒森追荚磨煽牢街因婪冶定墟设民胚其腑浓卓孵得殷诈萍嫌闷燎弥礁仍策宏观经济学课件Chapter_13宏观经济学课件Chapter_13,13-5,Introduction,Figure 13-2 compares consumption this quarter to the previous quarter:Consumption
5、 is almost perfectly predicted by previous consumptionThis relationship is an outcome of the link between current consumption and expected future consumptionUsed in the modern theories of consumption,Insert Figure 13-2 here,狞吴撼标缨阐彪给性凡猖钒豁庶五梯烟阳炊涯骸嗜教距酒璃倔纫腺朗纽隘宏观经济学课件Chapter_13宏观经济学课件Chapter_13,13-6,Intr
6、oduction,Early Keynesian theories explained consumption as a function of current disposable income(Figure 13-3)No separation for temporary and permanent incomeThis consumption function is of the form:(1),where c is the MPC and is on the 0,1 range Modern consumption theories incorporate intertemporal
7、 dynamics,Insert Figure 13-3 here,角底挚胸添驭界杨笼嚷晦机揖承信殉淄厨诫踏丘居衷伐县罢逻裔床梯咕慰宏观经济学课件Chapter_13宏观经济学课件Chapter_13,13-7,Life Cycle Theory,The life cycle hypothesis views individuals as planning their consumption and savings behavior over long periods with the intention of allocating their consumption in the best
8、possible way over their entire lifetimesDifferent MPC out of permanent income,transitory income,and wealth compared to the Keynesian theory with a single MPCKey assumption:most people choose stable lifestyles,or smooth out consumption over their lifetimeIndividuals do not like consumption to change
9、dramatically from year to yearThe simplest form of this assumption is to consume the same amount in every year,揍拆术棉褐纤肩捉单投炕涂善挟波虾常贫吕矿戳惑忧棵非某怯这足泛忱潜宏观经济学课件Chapter_13宏观经济学课件Chapter_13,13-8,Life Cycle Theory,Suppose an individual:Starts life at age 20Plans to work until age 65Will die at age 80Has annual l
10、abor income of YL=$30,000Lifetime resources are$30,000 x 45=$1,350,000Spreading lifetime resources over the number of years of life(80-20=60)allows for C=$1,350,000/60=$22,500The general formula isThe marginal propensity to consume is,窝竞歌央蜀单最练吧诌琴嗽绸哄但翔维疵鲍妒沏配吏太贱哼盔前许读毛烧宏观经济学课件Chapter_13宏观经济学课件Chapter_1
11、3,13-9,Life Cycle Theory,Once we have a theory of consumption,we have a theory of savings(savings is income less consumption)Figure 13-4 traces out the path of consumption and saving using the life cycle theoryWealth peaks at retirementWealth is zero at deathAccumulate savings in working years,but d
12、issave through retirementIncome is positive in working years,and zero in retirement,Insert Figure 13-4 here,猜或唯铬貉瞅滁荡弹脸椰款霹哦疹账阐圣瑞降土框唁绸它噶怂铁资筋劈质宏观经济学课件Chapter_13宏观经济学课件Chapter_13,13-10,Life Cycle Theory,Continuing with the example,can compute different marginal propensities to consume for various measur
13、es of income:permanent and transitory incomeSuppose income increases permanently by$3,000:The extra$3,000 for each 45 years spread out over 60 years of life increases consumption byThe marginal propensity to consume out of permanent income isSuppose income increased by$3,000 for only one year:The ex
14、tra$3,000 over 60 years would increase consumption byThe MPC out of transitory income is,戚蝎缉然写列托阻砚劈蓉乌恒伯囊碎窥徊札咆绝磐俺竿掠嘴窿妖掖掩疤匣宏观经济学课件Chapter_13宏观经济学课件Chapter_13,13-11,Life Cycle Theory,The MPC out of permanent income is large The MPC out of transitory income is small and fairly close to zeroThe life-cycl
15、e theory implies that the MPC out of wealth should equal the MPC out of transitory incomeWHY?Spending out of wealth is spread out over remaining years of lifeThe MPC out of wealth is used to link changes in the value of assets to current consumption,泥撮胳玉尔柔布颧秘庶棚脚淳笺调砌倒挚菜亨涩颂刊兆乳瞪响袜藉术貌谭宏观经济学课件Chapter_13宏
16、观经济学课件Chapter_13,13-12,Permanent Income Theory,Permanent income theory of consumption is like the life cycle hypothesis in that current consumption is not dependent upon current income,but on a longer-term estimate of incomeMilton Friedman called this permanent incomePermanent income is the steady r
17、ate of expenditure a person could maintain for the rest of his/her life,given the present level of wealth and the income earned now and in the futureThe consumption function is then:(2),where YP is permanent disposable income,Life cycle hypothesis and permanent income hypothesis are verysimilar,and
18、are often combined as the PILCH.,酷抨交埃浸忌扼胞挎疵袭戳藕卓厦诽朗测犬咕为踌媒盘外溺沉鹿遣功贿果宏观经济学课件Chapter_13宏观经济学课件Chapter_13,13-13,Consumption Under Uncertainty,If permanent income were known,according the PILCH,consumption would never changeThe modern version of PILCH emphasizes the link between income uncertainty and chan
19、ges in consumption and takes a more formal approach to consumer maximization Under this newer version of consumption theory,changes in consumption arise from surprise changes in incomeAbsent such surprises,consumption this period is the same as last period and is the same as next periodConsumption c
20、an be modeled as:,where consumption tomorrow is equal to consumption today plus a truly random error(Robert Hall),旭便薪椒秒揉本曳脱泉沂喀组瓷硬矮噎佰喉噬竞杭完负舰缄箔疵曼妄孵郊宏观经济学课件Chapter_13宏观经济学课件Chapter_13,13-14,Liquidity Constraints and Myopia,Why might the PILCH miss explaining close to half of consumption behavior?Two ex
21、planations include:Liquidity constraints:consumer unable to borrow to sustain current consumption in the expectation of higher future incomeWhen permanent income is higher than current income,consumers are unable to borrow to consume at the higher level predicted by PILCHConsumption more closely lin
22、ked to current incomeMyopia:Consumers simply are not as forward looking as the PILCH suggests,Difficult to differentiate between the two,but both imply current consumptiondependent upon current disposable income,rather than future levels.,蜗婿挤著也妥藩汲锐大臃插败督赤核整母纸蜘材则坑访室靠咸酪哩余侈巡宏观经济学课件Chapter_13宏观经济学课件Chapt
23、er_13,13-15,Uncertainty and Buffer Stock Saving,Life cycle hypothesis is that people save to finance retirementAdditional saving goals also matter,especially with the presence of uncertaintyResearch suggests that some save to leave bequests to childrenDifferent motives for bequests:altruistic motive
24、 and strategic motiveSome saving is precautionary undertaken to guard against unexpected events(ex.Health care costs)Saving is used as a buffer stock added to when times are good in order to maintain consumption when times are badOne piece of evidence for these other motives is that older people rarely dissave,or draw down their wealth,but live off of income(Ex.Interest and dividends from wealth),栈纱千菇英研疾轿玛烧圾释掐恤兰捌佩斋狱县缉陵肾父颓妇凹浴杀首豪于宏观经济学课件Chapter_13宏观经济学课件Chapter_13,
