LikeanEconomist宏观经济学-加州大学-詹姆斯·布

CHAPTER3ThinkingLikeanEconomist1QuestionsIseconomicsascience?Whatdoeconomistsmeanbyamodel?Whydoeconomistsusemathematicalmodelssomuch?Whatpatternsandhabitsofthoughtmustyoulearntosuccessfullythinklikeaneconomist?2Economicsisasocialsciencefocusesonhumanbeingsandhowtheybehavedebateswithineconomicslastlongerthanthoseinnaturalscienceslesslikelytoendinconsensuseconomistsareunabletoundertakelarge-scaleexperimentsthesubjectsstudiedbyeconomists--people--havemindsoftheirownexpectationsofthefutureplayanimportantrole3TheImportanceofExpectations:AnExampleThestockmarketcrashof1929changedwhatAmericansexpectedaboutthefutureoftheeconomyExpectationsthatfutureincomewouldbelowerbecamerealizedspendingproductionlayoffsincome4Figure3.1-TheStockMarket,1928-19325Economicsisaquantitativescienceusesarithmetictomeasureeconomicvariablesofinterestusesmathematicalmodelstorelateeconomicvariablesofinterestinvolvesaparticularwayofthinkingabouttheworldusinguniquetechnicallanguageaspecificsetofdata6Economistsuseaspecialsetofanalogiesandmetaphorstodescribethefunctioningofthemacroeconomycurves“shift”moneyhasa“velocity”thecentralbank“pushestheeconomyupthePhillipscurve”7Figure3.2-PushingtheEconomyUpthePhillipsCurve8DominantConceptstheimageofthe“circularflowofeconomicactivity”theuseoftheword“market”theideaof“equilibrium”useofgraphsanddiagramsequationsdepictedbygeometriccurvessituationsofequilibriumoccurwherecurvescrosschangesineconomydemonstratedbyshiftsinthecurves9TheCircularFlowpatternsofspending,income,andproductionflowingthroughtheeconomyflowofpurchasingpower10TheCircularFlow“incomeside”firmsbuythefactorsofproductionfromhouseholdsmoneypaymentsflowfromfirmstohouseholds“expenditureside”householdsbuygoodsandservicesfromfirmsmoneypaymentsflowfromhouseholdstofirms11Figure3.3-TheCircularFlowDiagram12CircularFlowcanbemadetobemorerealisticbyaddingthegovernmentfinancialmarketsinternationaltradeandfinance13Figure3.4-TheCircularFlowof

EconomicActivity14DifferentMeasuresoftheCircularFlow“expenditureside”measureconsumptioninvestmentgovernmentpurchasesnetexports“incomeside”measurepurchasesoflabor,capital,andnaturalresourcesowneddirectlyorindirectlybyhouseholds15DifferentMeasuresoftheCircularFlow“usesofincome”measurewherehouseholdsdecidetousetheirincomesavingtaxesconsumption16Marketsareusedasametaphorforthecomplexprocessesofmatchingandexchangethattakeplaceintheeconomyeconomistsassumethatbuyersandsellersarewell-informedaboutprevailingpricesandquantities17Equilibriumisapoint(orpoints)ofbalanceatwhichsomeeconomicquantityisneitherrisingnorfallingonceequilibriumisidentified,economistscandeterminehowfasteconomicforceswillpushtheeconomytothepointsofequilibrium18GraphsandEquationsanalgebraicequationrelatingtwovariablescanalsoberepresentedasacurvedrawnonagraphthesolutiontoasetoftwoequationsisthepointonagraphwherethetwocurvesthatrepresenttheequationsintersect19Figure3.5-TwoFormsoftheProductionFunction20UsingGraphsInsteadofEquationsbehavioralrelationshipsbecomecurvesthatshiftaroundonagraphconditionsofeconomicequilibriumcanberepresentedbythepointswherethecurvesdescribingbehavioralrelationshipsintersect21UsingGraphsInsteadofEquationschangesinthestateoftheeconomycanbeshownasmovementsintheintersectionofthecurves22BuildingModelsrestricttheproblemtoonlyafewbehavioralrelationshipsandequilibriumconditionscapturetheserelationshipsandequilibriumconditionsinsimplealgebraicequationsusediagramstorepresenttheequationsapplythemodeltotherealworld23ImportantConceptsinMacroeonomicModelsrepresentativeagentsassumethatallparticipantsintheeconomyarethesameexaminethedecision-makingofoneindividualandthengeneralizetotheeconomyasawhole24ImportantConceptsinMacroeonomicModelsopportunitycostsoccurwhenanydecisionismademeasuredbythevalueofthebestalternativeforegone25ImportantConceptsinMacroeonomicModelsexpectationformationmacroeconomicmodelsmustexplaintheamountoftimepeoplespendthinkingaboutthefuturetheinformationthatpeoplehaveavailabletherulesofthumbusedtoturninformationintoexpectations26ImportantConceptsinMacroeonomicModelsexpectationformationstaticexpectationsdecisionmakersdonotthinkaboutthefutureadaptiveexpectationsdecisionmakersassumethatthefutureisgoingtobeliketherecentpast27ImportantConceptsinMacroeonomicModelsexpectationformationrationalexpectationsdecisionmakersspendasmuchtimeastheycanthinkingaboutthefutureandknowasmuchaboutthestructureandbehavioroftheeconomyasthemodelbuilderdoes28BuildingandSolvinganEconomicModelwriteequationsthatrepresentbehavioralrelationshipsstatehowthe“effects”arerelatedtothe“causes”drawadiagramtohelpvisualizetherelationshipconsiderequilibriumconditionscanbeshownasintersectionsondiagram29BuildingandSolvinganEconomicModel:AnExampleTheproductionfunctionrelatestheeconomy’scapital-laborratio(K/L)theleveloftechnologyorefficiencyofthelaborforce(E)thelevelofrealGDPperworker(Y/L)Cobb-Douglasproductionfunction30BuildingandSolvinganEconomicModel:AnExampleEquilibriumconditionforbalancedgrowththeratiooftheeconomy’scapitalstock(K)toitslevelofoutput(Y)mustbeconstant31BuildingandSolvinganEconomicModel:AnExampleEquilibriumconditionforbalancedgrowths=shareoftotalincomeintheeconomysavedandinvestedn=proportionalgrowthrateofthelaborforceg=proportionalgrowthrateoftheefficiencyofthelaborforce=thedepreciationrate32BuildingandSolvinganEconomicModel:AnExamplearithmeticcanbeusedtodeterminethesteady-stateoutputperworkerLetE=$10,000,=1/2,s=25%,n=1%,g=1%,and=3%.33BuildingandSolvinganEconomicModel:AnExamplesinceK/Y=5,thismustimplythatK/L=5Y/LsubstitutingforandEtintheCobb-Douglasproductionfunction34BuildingandSolvinganEconomicModel:AnExampleinequilibrium,bothconditionsmusthold35BuildingandSolvinganEconomicModel:AnExamplealgebracanbeusedtodeterminethesteady-stateoutputperworker36BuildingandSolvinganEconomicModel:AnExampleputtinginthebalanced-growthcondition37BuildingandSolvinganEconomicModel:AnExampleLetE=$10,000,=1/2,s=25%,n=1%,g=1%,and=3%38BuildingandSolvinganEconomicModel:AnExamplegraphscanalsobeusedtoshowthesteady-stateoutputperworkertheproductionfunctioncanbedrawnwithoutputperworker(Y/L)ontheverticalaxisandcapitalperworker(K/L)onthehorizontalaxistheequilibriumconditionforbalancedgrowthcanalsobeshownK/L=s/(n+g+)

39Figure3.6-EquilibriumOutputperWorker40TheAdvantagesofUsingAlgebrabestwaytosummarizecause-and-effectbehavioralrelationshipsallowsustoconsiderdifferentpossiblesystematicrelationshipsbychangingthevalueofparameters41Figure3.7-ASingleEquation,aHost

ofRelationships42Figure3.8-ChangingParameterValuesandtheShapeoftheCobb-DouglasProductionFunction43Figure3.9-TheEffectofChangesintheEfficiencyofLaborontheShapeoftheProductionFunction44ChapterSummaryDon’tbesurp