微觀經(jīng)濟(jì)學(xué)（第八版-英文）課件：The Basics of Supply and Demand

2.1 SupplyandDemand2.2 TheMarketMechanism2.3 ChangesinMarketEquilibrium2.4 ElasticitiesofSupplyandDemand2.5 Short-RunversusLong-RunElasticities2.6 UnderstandingandPredictingtheEffectsofChangingMarketConditions2.7 EffectsofGovernmentIntervention—PriceControls

TheBasicsofSupplyandDemandCHAPTEROUTLINEUnderstandingandpredictinghowchangingworldeconomicconditionsaffectmarketpriceandproductionEvaluatingtheimpactofgovernmentpricecontrols,minimumwages,pricesupports,andproductionincentivesDetermininghowtaxes,subsidies,tariffs,andimportquotasaffectconsumersandproducersSupply-demandanalysisisafundamentalandpowerfultoolthatcanbeappliedtoawidevarietyofinterestingandimportantproblems.Tonameafew:TheSupplyCurve●

supplycurveRelationshipbetweenthequantityofagoodthatproducersarewillingtosellandthepriceofthegood.THESUPPLYCURVEThesupplycurve,labeledSinthefigure,showshowthequantityofagoodofferedforsalechangesasthepriceofthegoodchanges.Thesupplycurveisupwardsloping:Thehighertheprice,themorefirmsareableandwillingtoproduceandsell.Ifproductioncostsfall,firmscanproducethesamequantityatalowerpriceoralargerquantityatthesameprice.Thesupplycurvethenshiftstotheright(fromStoS′).FIGURE2.1SupplyandDemand2.1QS=QS(P)OTHERVARIABLESTHATAFFECTSUPPLYThequantitythatproducersarewillingtoselldependsnotonlyonthepricetheyreceivebutalsoontheirproductioncosts,includingwages,interestcharges,andthecostsofrawmaterials.Whenproductioncostsdecrease,outputincreasesnomatterwhatthemarketpricehappenstobe.Theentiresupplycurvethusshiftstotheright.Economistsoftenusethephrasechangeinsupplytorefertoshiftsinthesupplycurve,whilereservingthephrasechangeinthequantitysuppliedtoapplytomovementsalongthesupplycurve.THEDEMANDCURVEThedemandcurve,labeledD,showshowthequantityofagooddemandedbyconsumersdependsonitsprice.Thedemandcurveisdownwardsloping;holdingotherthingsequal,consumerswillwanttopurchasemoreofagoodasitspricegoesdown.Thequantitydemandedmayalsodependonothervariables,suchasincome,theweather,andthepricesofothergoods.Formostproducts,thequantitydemandedincreaseswhenincomerises.Ahigherincomelevelshiftsthedemandcurvetotheright(fromDtoD′).FIGURE2.2● demandcurveRelationshipbetweenthequantityofagoodthatconsumersarewillingtobuyandthepriceofthegood.TheDemandCurveQD=QD(P)SHIFTINGTHEDEMANDCURVEIfthemarketpricewereheldconstantatP1,wewouldexpecttoseeanincreaseinthequantitydemanded—say,fromQ1toQ2,asaresultofconsumers’higherincomes.Becausethisincreasewouldoccurnomatterwhatthemarketprice,theresultwouldbeashifttotherightoftheentiredemandcurve.SUBSTITUTEANDCOMPLEMENTARYGOODS●

substitutesTwogoodsforwhichanincreaseinthepriceofoneleadstoanincreaseinthequantitydemandedoftheother.●

complementsTwogoodsforwhichanincreaseinthepriceofoneleadstoadecreaseinthequantitydemandedoftheother.SUPPLYANDDEMANDThemarketclearsatpriceP0andquantityQ0.AtthehigherpriceP1,asurplusdevelops,sopricefalls.AtthelowerpriceP2,thereisashortage,sopriceisbidup.FIGURE2.3TheMarketMechanism2.2EQUILIBRIUM●

equilibrium(ormarketclearing)pricePricethatequatesthequantitysuppliedtothequantitydemanded.●

marketmechanismTendencyinafreemarketforpricetochangeuntilthemarketclears.●

surplusSituationinwhichthequantitysuppliedexceedsthequantitydemanded.●

shortageSituationinwhichthequantitydemandedexceedsthequantitysupplied.WHENCANWEUSETHESUPPLY-DEMANDMODEL?

Weareassumingthatatanygivenprice,agivenquantitywillbeproducedandsold.Thisassumptionmakessenseonlyifamarketisatleastroughlycompetitive.Bythiswemeanthatbothsellersandbuyersshouldhavelittlemarketpower—i.e.,littleabilityindividuallytoaffectthemarketprice.Supposeinsteadthatsupplywerecontrolledbyasingleproducer—amonopolist.Ifthedemandcurveshiftsinaparticularway,itmaybeinthemonopolist’sinteresttokeepthequantityfixedbutchangetheprice,ortokeepthepricefixedandchangethequantity.NEWEQUILIBRIUMFOLLOWING

SHIFTINSUPPLYWhenthesupplycurveshiftstotheright,themarketclearsatalowerpriceP3andalargerquantityQ3.FIGURE2.4ChangesinMarketEquilibrium2.3NEWEQUILIBRIUMFOLLOWINGSHIFTINDEMANDWhenthedemandcurveshiftstotheright,themarketclearsatahigherpriceP3andalargerquantityQ3.FIGURE2.5NEWEQUILIBRIUMFOLLOWINGSHIFTSINSUPPLYANDDEMANDSupplyanddemandcurvesshiftovertimeasmarketconditionschange.Inthisexample,rightwardshiftsofthesupplyanddemandcurvesleadtoaslightlyhigherpriceandamuchlargerquantity.Ingeneral,changesinpriceandquantitydependontheamountbywhicheachcurveshiftsandtheshapeofeachcurve.FIGURE2.6From1970to2010,thereal(constant-dollar)

priceofeggsfellby55percent,whilethereal

priceofacollegeeducationroseby82percent.Themechanizationofpoultryfarmssharply

reducedthecostofproducingeggs,shiftingthe

supplycurvedownward.Thedemandcurvefor

eggsshiftedtotheleftasamorehealth-

consciouspopulationtendedtoavoideggs.Asforcollege,increasesinthecostsofequippingandmaintainingmodernclassrooms,laboratories,andlibraries,alongwithincreasesinfacultysalaries,pushedthesupplycurveup.Thedemandcurveshiftedtotherightasalargerpercentageofagrowingnumberofhighschoolgraduatesdecidedthatacollegeeducationwasessential.EXAMPLE2.1THEPRICEOFEGGSANDTHEPRICEOFACOLLEGEEDUCATIONREVISITEDEXAMPLE2.1THEPRICEOFEGGSANDTHEPRICEOFACOLLEGEEDUCATIONREVISITED(a)MARKETFOREGGS(a)Thesupplycurveforeggsshifteddownwardasproductioncostsfell;thedemandcurveshiftedtotheleftasconsumerpreferenceschanged.Asaresult,therealpriceofeggsfellsharplyandeggconsumptionrose.FIGURE2.7(b)Thesupplycurveforacollegeeducationshiftedupasthecostsofequipment,maintenance,andstaffingrose.Thedemandcurveshiftedtotherightasagrowingnumberofhighschoolgraduatesdesiredacollegeeducation.Asaresult,bothpriceandenrollmentsrosesharply.(b)MARKETFORCOLLEGEEDUCATIONEXAMPLE2.2WAGEINEQUALITYINTHEUNITEDSTATESOverthepasttwodecades,thewagesofskilledhigh-incomeworkershavegrownsubstantially,whilethewagesofunskilledlow-incomeworkershavefallenslightly.From1978to2009,peopleinthetop20percentoftheincomedistributionexperiencedanincreaseintheiraveragereal(inflation-adjusted)pretaxhouseholdincomeof45percent,whilethoseinthebottom20percentsawtheiraveragerealpretaxincomeincreasebyonly4percent.Whilethesupplyofunskilledworkers—peoplewithlimitededucations—hasgrownsubstantially,thedemandforthemhasrisenonlyslightly.Ontheotherhand,whilethesupplyofskilledworkers—e.g.,engineers,scientists,managers,andeconomists—hasgrownslowly,thedemandhasrisendramatically,pushingwagesup.EXAMPLE2.3THELONG-RUNBEHAVIOROFNATURALRESOURCEPRICESCONSUMPTIONANDPRICEOFCOPPERAlthoughannualconsumptionofcopperhasincreasedaboutahundredfold,thereal(inflation-adjusted)pricehasnotchangedmuch.FIGURE2.8EXAMPLE2.3THELONG-RUNBEHAVIOROFNATURALRESOURCEPRICESLONG-RUNMOVEMENTSOFSUPPLYANDDEMANDFORMINERALRESOURCESAlthoughdemandformostresourceshasincreaseddramaticallyoverthepastcentury,priceshavefallenorrisenonlyslightlyinreal(inflation-adjusted)termsbecausecostreductionshaveshiftedthesupplycurvetotherightjustasdramatically.FIGURE2.9SUPPLYANDDEMANDFORNEWYORKCITYOFFICESPACEFollowing9/11thesupplycurveshiftedtotheleft,butthedemandcurvealsoshiftedtotheleft,sothattheaveragerentalpricefell.FIGURE2.10EXAMPLE2.4THEEFFECTSOF9/11ONTHESUPPLYANDDEMANDFORNEWYORKCITYOFFICESPACEelasticityPercentagechangeinonevariableresultingfroma1-percentincreaseinanother.priceelasticityofdemandPercentagechangeinquantitydemandedofagoodresultingfroma1-percentincreaseinitsprice.PRICEELASTICITYOFDEMAND(2.1)ElasticitiesofSupplyandDemand2.4lineardemandcurveDemandcurvethatisastraightline.LINEARDEMANDCURVELINEARDEMANDCURVEFIGURE2.11Thepriceelasticityofdemanddependsnotonlyontheslopeofthedemandcurvebutalsoonthepriceandquantity.Theelasticity,therefore,variesalongthecurveaspriceandquantitychange.Slopeisconstantforthislineardemandcurve.Nearthetop,becausepriceishighandquantityissmall,theelasticityislargeinmagnitude.Theelasticitybecomessmalleraswemovedownthecurve.infinitelyelasticdemandPrinciplethatconsumerswillbuyasmuchofagoodastheycangetatasingleprice,butforanyhigherpricethequantitydemandeddropstozero,whileforanylowerpricethequantitydemandedincreaseswithoutlimit.(a)INFINITELYELASTICDEMANDFIGURE2.12(a)Forahorizontaldemandcurve,?Q/?Pisinfinite.Becauseatinychangeinpriceleadstoanenormouschangeindemand,theelasticityofdemandisinfinite.LINEARDEMANDCURVEcompletelyinelasticdemandPrinciplethatconsumerswillbuyafixedquantityofagoodregardlessofitsprice.(b)COMPLETELYINELASTICDEMANDFIGURE2.12(b)Foraverticaldemandcurve,?Q/?Piszero.Becausethequantitydemandedisthesamenomatterwhattheprice,theelasticityofdemandiszero.LINEARDEMANDCURVEincomeelasticityofdemandPercentagechangeinthequantitydemandedresultingfroma1-percentincreaseinincome.OTHERDEMANDELASTICITIEScross-priceelasticityofdemandPercentagechangeinthequantitydemandedofonegoodresultingfroma1-percentincreaseinthepriceofanother.priceelasticityofsupplyPercentagechangeinquantitysuppliedresultingfroma1-percentincreaseinprice.ELASTICITIESOFSUPPLY(2.2)(2.3)pointelasticityofdemandPriceelasticityataparticularpointonthedemandcurve.PointversusArcElasticitiesarcelasticityofdemandPriceelasticitycalculatedoverarangeofprices.ARCELASTICITYOFDEMAND(2.4)EXAMPLE2.5THEMARKETFORWHEATDuringrecentdecades,changesinthewheatmarkethadmajorimplicationsforbothAmericanfarmersandU.S.agriculturalpolicy.Tounderstandwhathappened,let’sexaminethebehaviorofsupplyanddemandbeginningin1981.Bysettingthequantitysuppliedequaltothequantitydemanded,wecandeterminethemarket-clearingpriceofwheatfor1981:Supply:QS=1800+240PDemand:QD=3550?266PQS=QD1800+240P=3550?266P506P=1750P=$3.46perbushelSubstitutingintothesupplycurveequation,wegetQ=1800+(240)(3.46)=2630millionbushelsEXAMPLE2.5THEMARKETFORWHEATWeusethedemandcurvetofindthepriceelasticityofdemand:Wecanlikewisecalculatethepriceelasticityofsupply:Becausethesesupplyanddemandcurvesarelinear,thepriceelasticitieswillvaryaswemovealongthecurves.Thusdemandisinelastic.

Demand(a)GASOLINE:SHORT-RUNANDLONG-RUNDEMANDCURVESFIGURE2.13(a)Intheshortrun,anincreaseinpricehasonlyasmalleffectonthequantityofgasolinedemanded.Motoristsmaydriveless,buttheywillnotchangethekindsofcarstheyaredrivingovernight.Inthelongerrun,however,becausetheywillshifttosmallerandmorefuel-efficientcars,theeffectofthepriceincreasewillbelarger.Demand,therefore,ismoreelasticinthelongrunthanintheshortrun.Short-RunversusLong-RunElasticities2.5(b)AUTOMOBILES:SHORT-RUNANDLONG-RUNDEMANDCURVESFIGURE2.13(b)Theoppositeistrueforautomobiledemand.Ifpriceincreases,consumersinitiallydeferbuyingnewcars;thusannualquantitydemandedfallssharply.Inthelongerrun,however,oldcarswearoutandmustbereplaced;thusannualquantitydemandedpicksup.Demand,therefore,islesselasticinthelongrunthanintheshortrun.DEMANDANDDURABILITYINCOMEELASTICITIESIncomeelasticitiesalsodifferfromtheshortruntothelongrun.Formostgoodsandservices—foods,beverages,fuel,entertainment,etc.—theincomeelasticityofdemandislargerinthelongrunthanintheshortrun.Foradurablegood,theoppositeistrue.Theshort-runincomeelasticityofdemandwillbemuchlargerthanthelong-runelasticity.GDPANDINVESTMENTINDURABLEEQUIPMENTFIGURE2.14AnnualgrowthratesarecomparedforGDPandinvestmentindurableequipment.Becausetheshort-runGDPelasticityofdemandislargerthanthelong-runelasticityforlong-livedcapitalequipment,changesininvestmentinequipmentmagnifychangesinGDP.Thuscapitalgoodsindustriesareconsidered“cyclical.”CYCLICALINDUSTRIEScyclicalindustriesIndustriesinwhichsalestendtomagnifycyclicalchangesingrossdomesticproductandnationalincome.CONSUMPTIONOFDURABLESVERSUSNONDURABLESFIGURE2.15AnnualgrowthratesarecomparedforGDP,consumerexpendituresondurablegoods(automobiles,appliances,furniture,etc.),andconsumerexpendituresonnondurablegoods(food,clothing,services,etc.).Becausethestockofdurablesislargecomparedwithannualdemand,short-rundemandelasticitiesarelargerthanlong-runelasticities.Likecapitalequipment,industriesthatproduceconsumerdurablesare“cyclical”(i.e.,changesinGDParemagnified).Thisisnottrueforproducersofnondurables.EXAMPLE2.6THEDEMANDFORGASOLINEANDAUTOMOBILESTABLE2.1DEMANDFORGASOLINENUMBEROFYEARSALLOWEDTOPASSFOLLOWINGAPRICEORINCOMECHANGEELASTICITY123510Price0.2?0.3?0.4?0.5?0.8Income0.20.40.50.61.0TABLE2.2DEMANDFORAUTOMOBILESNUMBEROFYEARSALLOWEDTOPASSFOLLOWINGAPRICEORINCOMECHANGEELASTICITY123510Price?1.2?0.9?0.8?0.6?0.4Income3.02.31.91.41.0SupplySUPPLYANDDURABILITYCOPPER:SHORT-RUNANDLONG-RUNSUPPLYCURVESFIGURE2.16Likethatofmostgoods,thesupplyofprimarycopper,showninpart(a),ismoreelasticinthelongrun.Ifpriceincreases,firmswouldliketoproducemorebutarelimitedbycapacityconstraintsintheshortrun.Inthelongerrun,theycanaddtocapacityandproducemore.Part(b)showssupplycurvesforsecondarycopper.Ifthepriceincreases,thereisagreaterincentivetoconvertscrapcopperintonewsupply.Initially,therefore,secondarysupply(i.e.,supplyfromscrap)increasessharply.Butlater,asthestockofscrapfalls,secondarysupplycontracts.Secondarysupplyisthereforelesselasticinthelongrunthanintheshortrun.COPPER:SHORT-RUNANDLONG-RUNSUPPLYCURVESFIGURE2.16TABLE2.3SUPPLYOFCOPPERPRICEELASTICITYOF:SHORT-RUNLONG-RUNPrimarysupply0.201.60Secondarysupply0.430.31Totalsupply0.251.50EXAMPLE2.7THEWEATHERINBRAZILANDTHEPRICEOFCOFFEEINNEWYORKPRICEOFBRAZILIANCOFFEEFIGURE2.17WhendroughtsorfreezesdamageBrazil’scoffeetrees,thepriceofcoffeecansoar.Thepriceusuallyfallsagainafterafewyears,asdemandandsupplyadjust.SUPPLYANDDEMANDFORCOFFEEFIGURE2.18(1of3)(a)AfreezeordroughtinBrazilcausesthesupplycurvetoshifttotheleft.Intheshortrun,supplyiscompletelyinelastic;onlyafixednumberofcoffeebeanscanbeharvested.Demandisalsorelativelyinelastic;consumerschangetheirhabitsonlyslowly.Asaresult,theinitialeffectofthefreezeisasharpincreaseinprice,fromP0toP1.EXAMPLE2.7THEWEATHERINBRAZILANDTHEPRICEOFCOFFEEINNEWYORKSUPPLYANDDEMANDFORCOFFEEFIGURE2.18(2of3)EXAMPLE2.7THEWEATHERINBRAZILANDTHEPRICEOFCOFFEEINNEWYORK(b)Intheintermediaterun,supplyanddemandarebothmoreelastic;thuspricefallspartofthewayback,toP2.SUPPLYANDDEMANDFORCOFFEEFIGURE2.18(3of3)EXAMPLE2.7THEWEATHERINBRAZILANDTHEPRICEOFCOFFEEINNEWYORK(c)Inthelongrun,supplyisextremelyelastic;becausenewcoffeetreeswillhavehadtimetomature,theeffectofthefreezewillhavedisappeared.PricereturnstoP0.FITTINGLINEARSUPPLYANDDEMANDCURVESTODATAFIGURE2.19Linearsupplyanddemandcurvesprovideaconvenienttoolforanalysis.GivendatafortheequilibriumpriceandquantityP*andQ*,aswellasestimatesoftheelasticitiesofdemandandsupplyEDandES,wecancalculatetheparameterscanddforthesupplycurveandaandbforthedemandcurve.(Inthecasedrawnhere,c<0.)Thecurvescanthenbeusedtoanalyzethebehaviorofthemarketquantitatively.UnderstandingandPredictingtheEffectsofChangingMarketConditions2.6Step1:Step2:Demand:Q=a?bPSupply:Q=c+dPE=(P/Q)(?Q/?P)Demand:ED

=?b(P*/Q*)Supply:ES

=d(P*/Q*)a=Q*+bP*Q=a?bP+fI(2.5a)(2.5b)(2.6a)(2.6b)(2.7)Afterreachingalevelofabout$1.00perpoundin1980,thepriceofcopperfellsharplytoabout60centsperpoundin1986.Worldwiderecessionsin1980and1982contributedtothedeclineofcopperprices.Whydidthepriceincreasesosharplyafter2003?First,thedemandforcopperfromChinaandotherAsiancountriesbeganincreasingdramatically.Second,becausepriceshaddroppedsomuchfrom1996through2003,producersclosedunprofitableminesandcutproduction.Whatwouldadeclineindemanddotothepriceofcopper?Tofindout,wecanusethelinearsupplyanddemandcurves.EXAMPLE2.8THEBEHAVIOROFCOPPERPRICESEXAMPLE2.8THEBEHAVIOROFCOPPERPRICESCopperpricesareshowninbothnominal(noadjustmentforinflation)andreal(inflation-adjusted)terms.Inrealterms,copperpricesdeclinedsteeplyfromtheearly1970sthroughthemid-1980sasdemandfell.In1988–1990,copperpricesroseinresponsetosupplydisruptionscausedbystrikesinPeruandCanadabutlaterfellafterthestrikesended.Pricesdeclinedduringthe1996–2002periodbutthenincreasedsharplystartingin2005.COPPERPRICES,1965–2011FIGURE2.20COPPERSUPPLYANDDEMANDFIGURE2.21Theshiftinthedemandcurvecorrespondingtoa20-percentdeclineindemandleadstoa10.7-percentdeclineinprice.EXAMPLE2.8THEBEHAVIOROFCOPPERPRICESEXAMPLE2.9UPHEAVALINTHEWORLDOILMARKETPRICEOFCRUDEOILFIGURE2.22TheOPECcartelandpoliticaleventscausedthepriceofoiltorisesharplyattimes.Itlaterfellassupplyanddemandadjusted.Sincetheearly1970s,theworldoilmarkethasbeenbuffetedbytheOPECcartelandbypoliticalturmoilinthePersianGulf.EXAMPLE2.9UPHEAVALINTHEWORLDOILMARKETBecausethisexampleissetin2009–2011,allpricesaremeasuredin2011dollars.Herearesome