Chapter_13Consumption and Saving(宏观经济学,多恩布什,第十版)ppt课件

13-1,13-2,13,ConsumptionandSaving,ItemItemItemEtc.,13-3,Introduction,Consumptionaccountsforabout70%ofADFluctuationsinCareproportionatelysmallerthanthefluctuationsinGDPConsumptionisrelativelystableInthischapterweseektounderstandconsumptionandthelinkbetweenconsumptionandincomeConsumptiontheoryThedebateoverdifferentconsumptiontheories=debateoverthesizeofthemarginalpropensitytoconsume(MPC)KeynesianmodelMPCishigh,moderntheoriesMPCislow,13-4,Introduction,Figure13-2plotschangesinpercapitaconsumptionandchangesinpercapitadisposableincomeConsumptionfollowsincomeswingsthatlast5-10yearsConsumptiondoesnotrespondtospikesinincome,InsertFigure13-1here,Longtermchangesinincomegeneratechangesinconsumption,butshorttermchangesinincomedonot.,13-5,Introduction,Figure13-2comparesconsumptionthisquartertothepreviousquarter:ConsumptionisalmostperfectlypredictedbypreviousconsumptionThisrelationshipisanoutcomeofthelinkbetweencurrentconsumptionandexpectedfutureconsumptionUsedinthemoderntheoriesofconsumption,InsertFigure13-2here,13-6,Introduction,EarlyKeynesiantheoriesexplainedconsumptionasafunctionofcurrentdisposableincome(Figure13-3)NoseparationfortemporaryandpermanentincomeThisconsumptionfunctionisoftheform:(1),wherecistheMPCandisonthe0,1rangeModernconsumptiontheoriesincorporateintertemporaldynamics,InsertFigure13-3here,13-7,LifeCycleTheory,ThelifecyclehypothesisviewsindividualsasplanningtheirconsumptionandsavingsbehavioroverlongperiodswiththeintentionofallocatingtheirconsumptioninthebestpossiblewayovertheirentirelifetimesDifferentMPCoutofpermanentincome,transitoryincome,andwealthcomparedtotheKeynesiantheorywithasingleMPCKeyassumption:mostpeoplechoosestablelifestyles,orsmoothoutconsumptionovertheirlifetimeIndividualsdonotlikeconsumptiontochangedramaticallyfromyeartoyearThesimplestformofthisassumptionistoconsumethesameamountineveryyear,13-8,LifeCycleTheory,Supposeanindividual:Startslifeatage20Planstoworkuntilage65Willdieatage80HasannuallaborincomeofYL=$30,000Lifetimeresourcesare$30,000 x45=$1,350,000Spreadinglifetimeresourcesoverthenumberofyearsoflife(80-20=60)allowsforC=$1,350,000/60=$22,500ThegeneralformulaisThemarginalpropensitytoconsumeis,13-9,LifeCycleTheory,Oncewehaveatheoryofconsumption,wehaveatheoryofsavings(savingsisincomelessconsumption)Figure13-4tracesoutthepathofconsumptionandsavingusingthelifecycletheoryWealthpeaksatretirementWealthiszeroatdeathAccumulatesavingsinworkingyears,butdissavethroughretirementIncomeispositiveinworkingyears,andzeroinretirement,InsertFigure13-4here,13-10,LifeCycleTheory,Continuingwiththeexample,cancomputedifferentmarginalpropensitiestoconsumeforvariousmeasuresofincome:permanentandtransitoryincomeSupposeincomeincreasespermanentlyby$3,000:Theextra$3,000foreach45yearsspreadoutover60yearsoflifeincreasesconsumptionbyThemarginalpropensitytoconsumeoutofpermanentincomeisSupposeincomeincreasedby$3,000foronlyoneyear:Theextra$3,000over60yearswouldincreaseconsumptionbyTheMPCoutoftransitoryincomeis,13-11,LifeCycleTheory,TheMPCoutofpermanentincomeislargeTheMPCoutoftransitoryincomeissmallandfairlyclosetozeroThelife-cycletheoryimpliesthattheMPCoutofwealthshouldequaltheMPCoutoftransitoryincomeWHY?SpendingoutofwealthisspreadoutoverremainingyearsoflifeTheMPCoutofwealthisusedtolinkchangesinthevalueofassetstocurrentconsumption,13-12,PermanentIncomeTheory,Permanentincometheoryofconsumptionislikethelifecyclehypothesisinthatcurrentconsumptionisnotdependentuponcurrentincome,butonalonger-termestimateofincomeMiltonFriedmancalledthispermanentincomePermanentincomeisthesteadyrateofexpenditureapersoncouldmaintainfortherestofhis/herlife,giventhepresentlevelofwealthandtheincomeearnednowandinthefutureTheconsumptionfunctionisthen:(2),whereYPispermanentdisposableincome,Lifecyclehypothesisandpermanentincomehypothesisareverysimilar,andareoftencombinedasthePILCH.,13-13,ConsumptionUnderUncertainty,Ifpermanentincomewereknown,accordingthePILCH,consumptionwouldneverchangeThemodernversionofPILCHemphasizesthelinkbetweenincomeuncertaintyandchangesinconsumptionandtakesamoreformalapproachtoconsumermaximizationUnderthisnewerversionofconsumptiontheory,changesinconsumptionarisefromsurprisechangesinincomeAbsentsuchsurprises,consumptionthisperiodisthesameaslastperiodandisthesameasnextperiodConsumptioncanbemodeledas:,whereconsumptiontomorrowisequaltoconsumptiontodayplusatrulyrandomerror(RobertHall),13-14,LiquidityConstraintsandMyopia,WhymightthePILCHmissexplainingclosetohalfofconsumptionbehavior?Twoexplanationsinclude:Liquidityconstraints:consumerunabletoborrowtosustaincurrentconsumptionintheexpectationofhigherfutureincomeWhenpermanentincomeishigherthancurrentincome,consumersareunabletoborrowtoconsumeatthehigherlevelpredictedbyPILCHConsumptionmorecloselylinkedtocurrentincomeMyopia:ConsumerssimplyarenotasforwardlookingasthePILCHsuggests,Difficulttodifferentiatebetweenthetwo,butbothimplycurrentconsumptiondependentuponcurrentdisposableincome,ratherthanfuturelevels.,13-15,UncertaintyandBufferStockSaving,LifecyclehypothesisisthatpeoplesavetofinanceretirementAdditionalsavinggoalsalsomatter,especiallywiththepresenceofuncertaintyResearchsuggeststhatsomesavetoleavebequeststochildrenDifferentmotivesforbequests:altruisticmotiveandstrategicmotiveSomesavingisprecautionaryundertakentoguardagain