经济学（微观）（英文版原书第7版）课件 第6章　弹性：供给和需求的反应程度

EconomicsSeventhEditionChapter6Elasticity:TheResponsivenessofDemandandSupplyCopyright©2019,2017,2015PearsonEducation,Inc.AllRightsReserved.DoSodaTaxesWork?Recentlyanumberofcities,includingSanFrancisco,Chicago,andPhiladelphia,haveenactedtaxesonsodaandothersweetenedbeverages.Why?Toreducesugarconsumption,andhenceobesityanddiabetesToraisefundsforthegovernmentInterestingly,thesegoalspartiallyconflict:ifthebeverageconsumptiondecreasesasintended,thenlesstaxrevenuewillbecollected.Howcanweknowwhattheactualoutcomewillbe?ChapterOutline6.1

ThePriceElasticityofDemandandItsMeasurement6.2

TheDeterminantsofthePriceElasticityofDemand6.3

TheRelationshipbetweenPriceElasticityofDemandandTotalRevenue6.4

OtherDemandElasticities6.5

UsingElasticitytoAnalyzetheDisappearingFamilyFarm6.6

PriceElasticityofSupplyandItsMeasurement6.1ThePriceElasticityofDemandandItsMeasurementDefineandcalculatepriceelasticityofdemand.Asthepriceofsweetenedbeveragesincrease,weexpectpeoplewillbuyfewerofthem.Buthowmanyfewer?Howcanwecomeupwithasensiblewaytomeasurehowmuchquantitychangeswhenpricechanges?Oneideaistolookattheslopeofthedemandcurve.Butthiswon’twork,sincethevalueoftheslopedependsontheunitsusedtomeasureontheaxes.Instead,wedefineanelasticity,ameasureofhowmuchoneeconomicvariableresponsetochangesinanothereconomicvariable,basedonpercentagechangesinthevariables.PriceElasticityofDemandOurfirstelasticitytoexamineisthe

priceelasticityofdemand,theresponsivenessofthequantitydemandedtoachangeinprice:Althoughtheslopeandpriceelasticityofdemandarerelated,theyarenotthesamething.Sincepriceandquantitychangeinoppositedirectionsonthedemandcurve,thepriceelasticityofdemandisanegativenumber.Howeverweoftenreferto“morenegative”elasticitiesasbeing“larger”or“higher”.PriceElasticityofDemandTerminologyA“large”valueforthepriceelasticityofdemandmeansthatquantitydemandedchangesalotinresponsetoapricechange.Formally,wesaydemandiselastic

ifitspriceelasticityofdemandislarger(inabsolutevalue)than1.Soa10percentincreaseinpricewouldresultinagreaterthan10percentdecreaseinquantitydemanded.Demandisinelastic

ifitspriceelasticityofdemandissmaller(inabsolutevalue)than1.Thatis,closetozero,indicatingthatquantitydemandedchangeslittleinresponsetoapricechange.Demandisunit-elastic

ifthepriceelasticityofdemandisexactlyequalto1.Figure6.1ElasticandInelasticDemandAlongD1,cuttingthepricefrom$1.50to$1.35increasesthenumberofbottlessoldfrom1,000perdayto1,200perday;demandiselasticbetweenpointAandpointB.AlongD2,cuttingthepricefrom$1.50to$1.35increasesthenumberofbottlessoldfrom1,000perdayonlyto1,050perday;demandisinelasticbetweenpointAandpointC.PercentageChangesandtheMidpointFormulaPercentagechangeshavetheunfortunatepropertythatthepercentagechangefromAtoBisnotthenegativeofthepercentagechangefromBtoA.Example:Onthepreviousslide,frompointAtopointB,quantityincreasedfrom1,000to1,200,anincreaseof20percent.

HoweverfromBtoA,quantitydecreasesby16.7percent.ThiswouldmeantheelasticityfromAtoBwasdifferentfromtheelasticityfromBtoA,andundesirableproperty.Toavoidthis,weusethemidpointformulaforpercentagechanges:TheMidpointFormulaforElasticityThemidpointformulaavoidstheconfusionofwhetherwearegoingfromAtoBorfromBtoA:weusetheaverageofAandBinthedenominatorinsteadofchoosingoneofthem.Priceelasticityofdemandbecomes:Thisfirsttermisthepercentagechangeinquantity,usingthemidpointformula.Thesecondtermisthepercentagechangeinprice,usingthemidpointformula.CalculatingPriceElasticityofDemand(1of3)Atyourgrocerystore,youcutthepriceofCoca-Colafrom$1.50perbottleto$1.30perbottle.Coca-Colasaleswentupfrom2,000to2,500gallonsperday,asondemandcurveD1.Tocalculatethispriceelasticity,wefirstneedtheaveragequantityandprice:CalculatingPriceElasticityofDemand(2of3)Nowcalculatethepercentagechangeinquantityandprice:Thenpriceelasticityofdemandistheratioofthesetwo:Thisisgreaterinabsolutevaluethan−1,Sowesaythatdemandinthisrangeispriceelastic.CalculatingPriceElasticityofDemand(3of3)Whatifquantityhadonlyincreasedto2,100asindemandcurveD2?Percentagechangeinpriceremainsthesame(−14.3percent);howeverSopriceelasticityofdemandisnow:Thisissmaller(inabsolutevalue)than−1,sodemandisinelastic.ObservationsaboutElasticity(1of2)Whileslopeandelasticityarenotthesame,theyarerelated:Iftwodemandcurvesgothroughthesamepoint,theonewiththehigherslopealsohasthehigher(morenegative)elasticity.Averticaldemandcurvemeansthatquantitydemandeddoesnotchangeaspricechanges.Soelasticityiszero.Averticaldemandcurveisperfectlyinelastic.Perfectlyinelasticdemand:Thecasewherethequantitydemandediscompletelyunresponsivetopriceandthepriceelasticityofdemandequalszero.ObservationsaboutElasticity(2of2)Ahorizontaldemandcurvemeansquantitydemandedisinfinitelyresponsivetopricechanges.Elasticityisinfinite.Ahorizontaldemandcurveisperfectlyelastic.Perfectlyelasticdemand:Thecasewherethequantitydemandedisinfinitelyresponsivetopriceandthepriceelasticityofdemandequalsinfinity.Anotherspecialcaseoccurswhenadecreaseinpriceresultsinthesamepercentageincreaseinquantitydemanded;inthiscasewesaydemandisunitelastic.Table6.1SummaryofthePriceElasticityofDemand(1of5)Table6.1SummaryofthePriceElasticityofDemand(2of5)Table6.1SummaryofthePriceElasticityofDemand(3of5)Table6.1SummaryofthePriceElasticityofDemand(4of5)Table6.1SummaryofthePriceElasticityofDemand(5of5)Don’tConfuseInelasticwithPerfectlyInelasticForexample,gasolinedemandisinelastic;thequantitydemandeddoesnotchangemuchasthepriceofgasolinechanges.Itisnotperfectlyinelastic;itissomewhatresponsivetoprice.Whichpanelshowsthis?6.2TheDeterminantsofthePriceElasticityofDemandListandexplainthedeterminantsofthepriceelasticityofdemand.Whydosomegoodshaveahighpriceelasticityofdemand,whileothershavealowpriceelasticityofdemand?Thereareseveralcharacteristicsofthegood,ofthemarket,etc.thatdeterminethis.TheavailabilityofclosesubstitutesIfaproducthasmoresubstitutesavailable,itwillhavemoreelasticdemand.Example:Therearefewsubstitutesforgasoline,soitspriceelasticityofdemandislow.Example:TherearemanysubstitutesforNikes(Reeboks,Adidas,etc.),sotheirpriceelasticityofdemandishigh.MoreDeterminantsofthePriceElasticityofDemandThepassageoftimeOvertime,peoplecanadjusttheirbuyinghabitsmoreeasily.Elasticityishigherinthelongrunthantheshortrun.Example:Ifthepriceofgasolinerises,ittakesawhileforpeopletoadjusttheirgasolineconsumption.Howmighttheydothat?Buyingamorefuel-efficientcarMovingclosertoworkWhetherthegoodisaluxuryoranecessityPeoplearemoreflexiblewithluxuriesthannecessities,sopriceelasticityofdemandishigherforluxuries.Example:Manypeopleconsidermilkandbreadnecessities;theywillbuythemeveryweekalmostregardlessoftheprice.StillMoreDeterminantsofthePriceElasticityofDemandThedefinitionofthemarketThemorenarrowlydefinedthemarket,themoresubstitutesareavailable,andhencethemoreelasticisdemand.Example:Youmightbelievethereisnogoodsubstituteforjeans,soyourdemandforjeansisveryinelastic.Butifyouconsiderdifferentbrandsofjeans,youmightbemoresensitivetothepriceofaparticularbrand.Theshareofagoodinaconsumer’sbudgetIfagoodisasmallportionofyourbudget,youwilllikelynotbeverysensitivetoitsprice.Example:Youmightbuytablesaltonceayearorless;changesinitspricewillnotaffectverymuchhowmuchyoubuy.Table6.2EstimatedReal-WorldPriceElasticitiesofDemandProductEstimatedElasticityProductEstimatedElasticityBooks(Barnes&Noble)−4.00Water(residentialuse)−0.38Books(Amazon)−0.60Chicken−0.37DVDs(Amazon)−3.10Cocaine−0.28PostRaisinBran−2.50Cigarettes−0.25Newautomobiles−1.95Beer−0.29Tide(liquiddetergent)−3.92Catholicschoolattendance−0.19Coca-Cola−1.22Residentialnaturalgas−0.09Grapes−1.18Gasoline−0.06Soda−0.70Milk−0.04Restaurantmeals−0.67Sugar−0.04Healthinsurance(low-incomehouseholds)−0.65Uberride-hailingservice(fourlargecities)−0.50Bread−0.40

BlankBlankApplytheConcept:PriceElasticityofDemandforBreakfastCerealWhatisthepriceelasticityofdemandforbreakfastcereal?Theanswerdependsonwhetheryoumean:AparticularbrandofaparticularbreakfastcerealAparticularcategoryofbreakfastcerealBreakfastcerealingeneralThefurtherdownthelistwego,themorebroadlythemarketisdefined,andhencethefewerclosesubstitutesareavailable.Sowewouldexpectthepriceelasticityofdemandtobecomesmalleraswemovedownthelist.Andsoitdoes:CerealPriceelasticityofdemandPostRaisinBran−2.5Allfamilybreakfastcereals−1.8Alltypesofbreakfastcereal−0.96.3TheRelationshipbetweenPriceElasticityofDemandandTotalRevenueExplaintherelationshipbetweenthepriceelasticityofdemandandtotalrevenue.Ifyouareabusinessowner,youneedtodecidehowtopriceyourproduct.“HowmanycustomerswillIgainifIcutmyprice?”“WhatwillhappentomytotalrevenueifIcutmyprice?”Totalrevenue:Thetotalamountoffundsreceivedbyasellerofagoodorservice,calculatedbymultiplyingthepriceperunitbythenumberofunitssold.Knowingthepriceelasticityofdemandforyourproductcanhelptoanswerthesequestions.EffectofCuttingPricewithDifferentElasticitiesSupposedemandforyourproductisrelativelypriceinelastic.Customersarenotverysensitivetothepriceofyourproduct.Asyoudecreasetheprice,youexpecttogainfewadditionalcustomers.Thefewadditionalcustomersdonotcompensateforthelostrevenue,sooverallrevenuegoesdown.Supposedemandforyourproductisrelativelypriceelastic.Customersareverysensitivetothepriceofyourproduct.Asyoudecreasetheprice,youexpecttogainmanyadditionalcustomers.Themanyadditionalcustomersmorethancompensateforthelostrevenue,sooverallrevenuegoesup.Figure6.2TheRelationshipbetweenPriceElasticityandTotalRevenue(1of2)Revenuebeforepricecut(atA):1,000×

$1.50=$1,500Revenueafterpricecut(atB):1,050×

$1.35=$1,417.50Thedecreaseinpricedoesnotgenerateenoughextracustomers(areaE)tooffsetrevenueloss(areaC).Figure6.2TheRelationshipbetweenPriceElasticityandTotalRevenue(2of2)Revenuebeforepricecut(atA):1,000×

$1.50=$1,500Revenueafterpricecut(atB):1,200×

$1.35=$1,620Thedecreaseinpricedoesgeneratesenoughextracustomers(areaE)tomorethanoffsetrevenueloss(areaC).Table6.3TheRelationshipbetweenPriceElasticityandRevenueIfdemandis…then…because…elasticanincreaseinpricereducesrevenuethedecreaseinquantitydemandedisproportionallygreaterthantheincreaseinprice.elasticadecreaseinpriceincreasesrevenuetheincreaseinquantitydemandedisproportionallygreaterthanthedecreaseinprice.inelasticanincreaseinpriceincreasesrevenuethedecreaseinquantitydemandedisproportionallysmallerthantheincreaseinprice.inelasticadecreaseinpricereducesrevenuetheincreaseinquantitydemandedisproportionallysmallerthanthedecreaseinprice.unitelasticanincreaseinpricedoesnotaffectrevenuethedecreaseinquantitydemandedisproportionallythesameastheincreaseinprice.unitelasticadecreaseinpricedoesnotaffectrevenuetheincreaseinquantitydemandedisproportionallythesameasthedecreaseinprice.WhyAreElasticityandTotalRevenueRelated?Theformulaforpriceelasticityofdemandis:Soifthisisgreaterthan1(inabsoluteterms)thenquantitydemandedgoesupbyahigherpercentagethanprice,raisingtherevenue.

Aspecialcaseoccurswhenpriceelasticityofdemandis−1:thepercentagechangeinquantitydemandedequalsthepercentagechangeinpricesorevenuedoesnotchange.Figure6.3ElasticityIsNotConstantalongaLinearDemandCurve(1of2)Supposewehavealineardemandcurve.Whathappenstototalrevenueaspriceincreases?Initially,totalrevenuerises,suggestingdemandisinelastic.Butthentotalrevenuestartstofall,suggestingdemandiselastic!PriceQuantityDemandedTotalRevenue$80$072146424563048323103021224114140160Figure6.3ElasticityIsNotConstantalongaLinearDemandCurve(2of2)Thedatafromthetableareplottedinthegraphs.Aspricedecreasesfrom$8,revenuerises—hencedemandiselastic.Aspricecontinuestofall,revenueeventuallyflattensout—demandisunitelastic.Thenaspricefallsevenfurther,revenuebeginstofall—demandisinelastic.EstimatingPriceElasticityofDemandWecanseethatknowingthepriceelasticityofdemandwouldbeveryusefulforafirm.Buthowcanafirmknowthisinformation?Forawell-establishedproduct,economistscanusehistoricaldatatoestimatethedemandcurve.Tocalculatethepriceelasticityofdemandforanewproduct,firmsoftenrelyonmarketexperiments.Withmarketexperiments,firmstrydifferentpricesandobservethechangeinquantitydemandedthatresults.ApplytheConcept:WhyDoesAmazonCareaboutPriceElasticity?AmazonandbookpublisherHachettedisagreedonpricingofe-booksin2014.AmazonestimatedthatthepriceelasticityofdemandforHachette’se-bookswas−1.35,sodecreasingtheirpricewouldincreasetotalrevenue:PriceofBookCopiesSoldTotalRevenue$14.99100,000$1,499,000$9.99174,000$1,738,260HachettebelievedthedemandforbooksbyitsbestsellingauthorslikeJamesPattersonandJ.K.Rowlingmightbepriceelastic,butdemandforbooksbyless-well-knownauthorswouldbepriceinelastic.AmazonagreedtoletHachettechooseitsownpricing.Whatotherfactorsdoyouthinkmatterhere?6.4OtherDemandElasticitiesDefineandcalculatethecross-priceelasticityofdemandandtheincomeelasticityofdemandandexplaintheirdeterminants.WhenweexamineddemandinChapter3,wediscussedsubstitutesandcomplements:Substitutes:Goodsandservicesthatcanbeusedforthesamepurpose.Complements:Goodsandservicesthatareusedtogether.Cross-priceelasticityofdemand

isthepercentagechangeinthequantitydemandedofonegooddividedbythepercentagechangeinthepriceofanothergood.Itmeasuresthestrengthofsubstituteorcomplementrelationshipsbetweengoods.Table6.4SummaryofCross-PriceElasticityofDemandIftheproductsare…thenthecross-priceelasticityofdemandwillbe…ExampleSubstitutespositive.TwobrandsofsmartphonesComplementsnegative.iPhonesandapplicationsdownloadedfromonlinestoresUnrelatedzero.iPhonesandpeanutbutterIncomeElasticityofDemandWhenweexamineddemandinChapter3,wediscussednormalandinferiorgoods.Normalgoods:GoodsandservicesforwhichthequantitydemandedincreasesasincomeincreasesInferiorgoods:GoodsandservicesforwhichthequantitydemandedfallsasincomeincreasesIncomeelasticityofdemand

isameasureoftheresponsivenessofthequantitydemandedtochangesinincome,measuredbythepercentagechangeinthequantitydemandeddividedbythepercentagechangeinincome.Table6.5SummaryofIncomeElasticityofDemandIftheincomeelasticityofdemandis…thenthegoodis…Examplepositivebutlessthan1normalandanecessity.Breadpositiveandgreaterthan1normalandaluxury.Caviarnegativeinferior.High-fatmeatApplytheConcept:ElasticitiesofAlcoholicBeveragesChristopherRuhmoftheUniversityofVirginiaandcolleaguesestimatedelasticitiesforvariousalcoholicbeverages.Accordingtotheirstudy:Demandforbeerispriceinelastic.Beerandwinearecomplements.Beerandspiritsarealsocomplements,buttherelationshipisnotasstrong.Beerisanormalgood;anecessity.Areanyoftheseresultssurprisingtoyou?Whyorwhynot?Priceelasticityofdemandforbeer−0.30Cross-priceelasticityofdemandbetweenbeerandwine−0.83Cross-priceelasticityofdemandbetweenbeerandspirits−0.50Incomeelasticityofdemandforbeer0.096.5UsingElasticitytoAnalyzetheDisappearingFamilyFarmUsepriceelasticityandincomeelasticitytoanalyzeeconomicissues.Overthelastcenturyfarmshavebecomemuchmoreefficientatproducingfood.Thismightappeartomakefarmingmoreprofitable,andhenceencouragemorepeopleintofarming.Butthenumberofpeopleinfarminghasfallensubstantially(23millionin1950,3millionin2011).Whyhaveproductivitygainsinfarmingledtofewerpeoplechoosingtofarm?Figure6.4ElasticityandtheDisappearingFamilyFarm(1of3)In1950,U.S.farmersproduced1.0billionbushelsofwheatatapriceof$19.23perbushel.Overthenext67years,rapidincreasesinfarmproductivitycausedalargeshifttotherightinthesupplycurveforwheat.Figure6.4ElasticityandtheDisappearingFamilyFarm(2of3)Incomeelasticityofdemandforwheatislow,sodemandforwheatincreasedlittleoverthisperiod.Demandforwheatisalsoinelastic,sothelargeshiftinthesupplycurveandthesmallshiftinthedemandcurveresultedinasharpdeclineinthepriceofwheat.Figure6.4ElasticityandtheDisappearingFamilyFarm(3of3)Incombination,thisledtoadramaticfallinthepriceofthefarmers’output.Makingalivingonasmallfarmhasbecomeharderandharder,sotheincreaseinoutputissuppliedbyfewerandfewerlarge-scalefarmers.6.6ThePriceElasticityofSupplyandItsMeasurementDefinepriceelasticityofsupplyandexplainitsdeterminantsandhowitismeasured.Priceelasticityofsupplyistheresponsivenessofthequantitysuppliedtoachangeinprice,measuredbydividingthepercentagechangeinthequantitysuppliedofaproductbythepercentagechangeintheproduct’sprice.Itisverymuchanalogoustopriceelasticityofdemand:Sothesamesortofcalculationmethodsapply(midpointformula,etc.).DeterminantsofthePriceElasticityofSupplyPriceelasticityofsupplydependsontheabilityandwillingnessoffirmstoalterthequantitytheyproduceaspriceincreases.Thetimeperiodinquestioniscriticallyimportantfordeterminingthepriceelasticityofsupply.Supposethewholesalepriceofgrapesdoubledovernight:Farmerscoulddolittletoincreasetheirquantityimmediately;theinitialpriceelasticityofsupplywouldbecloseto0.Overtime,farmerscouldplantmorefieldsingrapes;sooverthecourseofseveralyears,thepriceelasticityofsupplywouldrise.ApplytheConcept:WhyAreOilPricesSoUnstable?(1of2)Oilproducerscannotchangeoutputveryquickly.Whendemandincreasessuddenly,pricerises,actingasarationingmechanismfortheincreaseddemand.ApplytheConcept:WhyAreOilPricesSoUnstable?(2of2)Similarly,consumersofoilarerelativelyinflexible,respondinglittletoshort-runchangesinprice.Duringthe2010s,newoilproductiontechnologyknownasfrackingincreasedthesupplyofoil;consequently,thepricefelldramaticallytomaintainequilibrium.ExtremeCases:PerfectlyElasticandPerfectlyInelasticSupplyIfasupplycurveisaverticalline,wesayitisperfectlyinelastic.Quantitysuppliediscompletelyunresponsivetoprice.Priceelasticityofsupplyequalszero.Example:Fixednumberofspacesinaparkinglot.Ifasupply