宏观经济学（第十三版）课件：Investment Spending

InvestmentSpending

.IntroductionInvestment:LinksthepresenttothefutureLinksthegoodsandmoneymarketsDrivesmuchofthebusinesscycleInthischapterwestudyhowinvestmentdependsoninterestratesandincome15-2IntroductionThetheoryofinvestmentisthetheoryofthedemandforcapitalInvestmentistheflowofspendingthataddstothestockofcapitalBothGDPandinvestmentareflowvariablesCapitalisthedollarvalueofallthebuildings,machines,andinventoriesatagivenpointintime

stockvalueInvestmentistheamountspentbybusinessestoaddtotheexistingcapitalstockoveragivenperiodFlowofinvestmentisquitesmallcomparedtothestockofcapital15-3TheDesiredCapitalStockFirmsusecapital,alongwithlaborandotherresources,toproduceoutput

ThegoalofagivenfirmistomaximizeprofitsWhendecidingtheoptimallevelofcapital,firmsmustbalancethecontributionthatmorecapitalmakestotheirrevenuesagainstthecostofacquiringadditionalcapitalThemarginalproductofcapitalistheincreaseinoutputproducedbyusingonemoreunitofcapitalinproductionTherental(user)costofcapitalisthecostofusingonemoreunitofcapitalinproduction15-4TheDesiredCapitalStockToderivetherentalcostofcapital:firmsfinancethepurchaseofcapitalbyborrowingovertime,ataninterestrateofiInthepresenceofinflation,thenominaldollarvalueofcapitalrisesovertimeAtthetimethefirmmakesaninvestment,thenominalinterestrateisknown,buttheinflationrateforthecomingyearisnotCapitalwearsoutovertimemustincludedepreciation,dThecompleteformulafortherentalcostofcapitalis:15-5TheDesiredStockofCapital

15-6Firmsaddcapitaluntilthemarginalreturnofthelastunit=rentalcostofcapitalDiminishingmarginalproductofcapitalAnincreaseintherentalcostofcapitalcanonlybejustifiedbyanincreaseinthemarginalproductofcapitalandalowerlevelofKThegeneralrelationshipamongthedesiredcapitalstock,K*,rc,andoutputis(1)FromDesiredCapitalStocktoInvestmentAttheinitiallevelofcapital,K0,priceofcapitaljusthighenoughtogenerateenoughinvestment,I0,toreplacethedepreciatingcapitalIntheLR,supplyofnewcapitalisveryelastic;increaseindemandismetwithoutmuchchangeinpriceIntheSR,pricerisestoP1,increasinginvestmentflowtoI115-7CapitalStockAdjustmentTheflexibleacceleratormodelcanbeusedtoexplainthespeedatwhichfirmsplantoadjusttheircapitalstockBasicnotion:thelargerthegapbetweentheexistingcapitalstockandthedesiredcapitalstock,themorerapidafirm’srateofinvestmentFirmsplantocloseafraction,,ofthegapbetweentheactualanddesiredcapitalstockseachperiodCapitalattheendoflastperiodisK-1Thegapbetweenactualanddesiredcapitalstockis(K*-K-1)AfirmplanstoaddafractionofthegaptolastperiodsstockActualcapitalstockattheendofthecurrentperiodisthen

(2)15-8CapitalStockAdjustment

15-9ToincreasethecapitalstockfromK-1toK0,thefirmmustachievenetinvestmentof:(3)Figure15-5illustrateshowthecapitalstockadjustsfromaninitiallevelofK-1tothedesiredlevelK*UpperpanelshowsthestockofcapitalLowerpanelshowsthecorrespondinglevelofICapitalStockAdjustment

15-10ToincreasethecapitalstockfromK-1toK0,thefirmmustachievenetinvestmentof:(3)Equation(3)showsinvestmentspendingasafunctionofK*andK-1AnyfactorthatincreasesK*,increasestherateofinvestmentInvestmentcontainsaspectsofdynamicbehavior

InvestmentSubsectorsFigure15-6demonstratesthevolatilityofthethreeinvestmentsubsectors:BusinessfixedinvestmentResidentialinvestmentInventoryinvestment15-11InvestmentSubsectorsFigure15-6demonstratesthevolatilityofthethreeinvestmentsubsectors:BusinessfixedinvestmentisthelargestofthethreeInventoryinvestmentisthemostvolatile15-12InvestmentSubsectorsFigure15-7showsresidentialinvestmentspendingasapercentageofGDPANDthenominalmortgageinterestrateovertimeResidentialinvestmentishighwhenmortgageratesarelowResidentialinvestmentislowwhenmortgageratesarehigh15-13InvestmentSubsectorsInventoriesincluderawmaterials,goodsintheproductionprocess,andcompletedgoodsheldbyfirmsintheanticipationoftheproducts’saleFigure15-8showstheratioofmanufacturinginventoriestosalesovertimeUntil1990,ratioonrangeof13to17percentSincefallentocloseto11percent(just-in-timemanufacturingtechniques)15-14InvestmentSubsectorsFirmsholdinventoriesforseveralreasons:Tomeetfuturedemandforgoods,becausegoodscannotbeinstantlymanufacturedorobtainedtomeetdemandItislesscostlyforafirmtoordergoodslessfre