最新微观经济学原理曼昆英文第五章精品课件

ElasticityanditsApplicationEconomicsPRINCIPLESOFN.GregoryMankiw5第一页，共51页。Inthischapter,lookfortheanswerstothesequestions:Whatiselasticity?Whatkindsofissuescanelasticityhelpusunderstand?Whatisthepriceelasticityofdemand?Howisitrelatedtothedemandcurve?Howisitrelatedtorevenue&expenditure?Whatisthepriceelasticityofsupply?Howisitrelatedtothesupplycurve?Whataretheincomeandcross-priceelasticitiesofdemand?*第二页，共51页。Youdesignwebsitesforlocalbusinesses.Youcharge$200perwebsite,andcurrentlysell12websitespermonth.Yourcostsarerising(includingtheopportunitycostofyourtime),soyouconsiderraisingthepriceto$250.Thelawofdemandsaysthatyouwon’tsellasmanywebsitesifyouraiseyourprice.Howmanyfewerwebsites?Howmuchwillyourrevenuefall,ormightitincrease?Ascenario…0*第三页，共51页。ELASTICITYANDITSAPPLICATION*ElasticityBasicidea:Elasticitymeasureshowmuchonevariablerespondstochangesinanothervariable.Onetypeofelasticitymeasureshowmuchdemandforyourwebsiteswillfallifyouraiseyourprice.Definition:ElasticityisanumericalmeasureoftheresponsivenessofQdorQstooneofitsdeterminants.0第四页，共51页。ELASTICITYANDITSAPPLICATION*PriceElasticityofDemandPriceelasticityofdemandmeasureshowmuchQdrespondstoachangeinP.Priceelasticityofdemand=PercentagechangeinQdPercentagechangeinPLooselyspeaking,itmeasurestheprice-sensitivityofbuyers’demand.0第五页，共51页。ELASTICITYANDITSAPPLICATION*PriceElasticityofDemandPriceelasticityofdemandequals0PQDQ2P2P1Q1Prisesby10%Qfallsby15%15%10%=1.5Priceelasticityofdemand=PercentagechangeinQdPercentagechangeinPExample:第六页，共51页。ELASTICITYANDITSAPPLICATION*PriceElasticityofDemandAlongaDcurve,PandQmoveinoppositedirections,whichwouldmakepriceelasticitynegative.Wewilldroptheminussignandreportallpriceelasticitiesaspositivenumbers.0PQDQ2P2P1Q1Priceelasticityofdemand=PercentagechangeinQdPercentagechangeinP第七页，共51页。ELASTICITYANDITSAPPLICATION*CalculatingPercentageChanges0PQD$2508B$20012ADemandforyourwebsitesStandardmethodofcomputingthepercentage(%)change:endvalue–startvaluestartvaluex100%GoingfromAtoB,the%changeinPequals($250–$200)/$200=25%第八页，共51页。ELASTICITYANDITSAPPLICATION*CalculatingPercentageChanges0PQD$2508B$20012ADemandforyourwebsitesProblem:Thestandardmethodgivesdifferentanswersdependingonwhereyoustart.FromAtoB,Prises25%,Qfalls33%,elasticity=33/25=1.33FromBtoA,Pfalls20%,Qrises50%,elasticity=50/20=2.50第九页，共51页。ELASTICITYANDITSAPPLICATION*CalculatingPercentageChangesSo,weinsteadusethemidpointmethod:0endvalue–startvaluemidpointx100%Themidpointisthenumberhalfwaybetweenthestart&endvalues,theaverageofthosevalues.Itdoesn’tmatterwhichvalueyouuseasthe“start”andwhichasthe“end”–yougetthesameanswereitherway!第十页，共51页。ELASTICITYANDITSAPPLICATION*CalculatingPercentageChangesUsingthemidpointmethod,the%changeinPequals0$250–$200$225x100%=22.2%The%changeinQequals12–810x100%=40.0%Thepriceelasticityofdemandequals40/22.2=1.8第十一页，共51页。ACTIVELEARNING1Calculateanelasticity*Usethefollowinginformationtocalculatethepriceelasticityofdemandforhotelrooms:ifP=$70,Qd=5000ifP=$90,Qd=3000第十二页，共51页。ELASTICITYANDITSAPPLICATION*Whatdeterminespriceelasticity?Tolearnthedeterminantsofpriceelasticity,welookataseriesofexamples.Eachcomparestwocommongoods.Ineachexample:Supposethepricesofbothgoodsriseby20%.ThegoodforwhichQdfallsthemost(inpercent)hasthehighestpriceelasticityofdemand.Whichgoodisit?Why?Whatlessondoestheexampleteachusaboutthedeterminantsofthepriceelasticityofdemand?0第十三页，共51页。ELASTICITYANDITSAPPLICATION*EXAMPLE1:Breakfastcerealvs.SunscreenThepricesofbothofthesegoodsriseby20%.ForwhichgooddoesQddropthemost?Why?Breakfastcerealhasclosesubstitutes(e.g.,pancakes,waffles,pizza),sobuyerscaneasilyswitchifthepricerises.Sunscreenhasnoclosesubstitutes,soconsumerswouldprobablynotbuymuchlessifitspricerises.Lesson:Priceelasticityishigherwhenclosesubstitutesareavailable.0第十四页，共51页。ELASTICITYANDITSAPPLICATION*EXAMPLE2:“BlueJeans”vs.“Clothing”Thepricesofbothgoodsriseby20%.ForwhichgooddoesQddropthemost?Why?Foranarrowlydefinedgoodsuchasbluejeans,therearemanysubstitutes(khakis,shorts).Therearefewersubstitutesavailableforbroadlydefinedgoods.(Therearen’ttoomanysubstitutesforclothing,otherthanlivinginanudistcolony.)Lesson:Priceelasticityishigherfornarrowlydefinedgoodsthanbroadlydefinedones.0第十五页，共51页。ELASTICITYANDITSAPPLICATION*EXAMPLE3:Insulinvs.CaribbeanCruisesThepricesofbothofthesegoodsriseby20%.ForwhichgooddoesQddropthemost?Why?Tomillionsofdiabetics,insulinisanecessity.Ariseinitspricewouldcauselittleornodecreaseindemand.Acruiseisaluxury.Ifthepricerises,somepeoplewillforegoit.Lesson:Priceelasticityishigherforluxuriesthanfornecessities.0第十六页，共51页。ELASTICITYANDITSAPPLICATION*EXAMPLE4:GasolineintheShortRunvs.GasolineintheLongRunThepriceofgasolinerises20%.DoesQddropmoreintheshortrunorthelongrun?Why?There’snotmuchpeoplecandointheshortrun,otherthanridethebusorcarpool.Inthelongrun,peoplecanbuysmallercarsorliveclosertowheretheywork.Lesson:Priceelasticityishigherinthelongrunthantheshortrun.0第十七页，共51页。ELASTICITYANDITSAPPLICATION*TheDeterminantsofPriceElasticity:ASummaryThepriceelasticityofdemanddependson:theextenttowhichclosesubstitutesareavailablewhetherthegoodisanecessityoraluxuryhowbroadlyornarrowlythegoodisdefinedthetimehorizon–elasticityishigherinthelongrunthantheshortrun0第十八页，共51页。ELASTICITYANDITSAPPLICATION*TheVarietyofDemandCurvesThepriceelasticityofdemandiscloselyrelatedtotheslopeofthedemandcurve.Ruleofthumb:Theflatterthecurve,thebiggertheelasticity.Thesteeperthecurve,thesmallertheelasticity.FivedifferentclassificationsofDcurves.…0第十九页，共51页。ELASTICITYANDITSAPPLICATION*Q1P1D“Perfectlyinelasticdemand”(oneextremecase)PQP2Pfallsby10%Qchangesby0%00%10%=0Priceelasticityofdemand=%changeinQ%changeinP=Consumers’pricesensitivity:Dcurve:Elasticity:verticalnone0第二十页，共51页。ELASTICITYANDITSAPPLICATION*D“Inelasticdemand”PQQ1P1Q2P2Qriseslessthan10%0<10%10%<1Priceelasticityofdemand=%changeinQ%changeinP=Pfallsby10%Consumers’pricesensitivity:Dcurve:Elasticity:relativelysteeprelativelylow<1第二十一页，共51页。ELASTICITYANDITSAPPLICATION*D“Unitelasticdemand”PQQ1P1Q2P2Qrisesby10%010%10%=1Priceelasticityofdemand=%changeinQ%changeinP=Pfallsby10%Consumers’pricesensitivity:Elasticity:intermediate1Dcurve:intermediateslope第二十二页，共51页。ELASTICITYANDITSAPPLICATION*D“Elasticdemand”PQQ1P1Q2P2Qrisesmorethan10%0>10%10%>1Priceelasticityofdemand=%changeinQ%changeinP=Pfallsby10%Consumers’pricesensitivity:Dcurve:Elasticity:relativelyflatrelativelyhigh>1第二十三页，共51页。ELASTICITYANDITSAPPLICATION*D“Perfectlyelasticdemand”(theotherextreme)PQP1Q1Pchangesby0%Qchangesbyany%0any%0%=infinityQ2P2=Consumers’pricesensitivity:Dcurve:Elasticity:infinityhorizontalextremePriceelasticityofdemand=%changeinQ%changeinP=第二十四页，共51页。ELASTICITYANDITSAPPLICATION*ElasticityofaLinearDemandCurve0Theslopeofalineardemandcurveisconstant,butitselasticityisnot.PQ$302010$00204060200%40%=5.0E=67%67%=1.0E=40%200%=0.2E=第二十五页，共51页。ELASTICITYANDITSAPPLICATION*PriceElasticityandTotalRevenueContinuingourscenario,ifyouraiseyourpricefrom$200to$250,wouldyourrevenueriseorfall?Revenue=PxQApriceincreasehastwoeffectsonrevenue:HigherPmeansmorerevenueoneachunityousell.Butyousellfewerunits(lowerQ),duetoLawofDemand.Whichofthesetwoeffectsisbigger?Itdependsonthepriceelasticityofdemand.0第二十六页，共51页。ELASTICITYANDITSAPPLICATION*PriceElasticityandTotalRevenueIfdemandiselastic,thenpriceelast.ofdemand>1%changeinQ>%changeinPThefallinrevenuefromlowerQisgreaterthantheincreaseinrevenuefromhigherP,sorevenuefalls.Revenue=PxQPriceelasticityofdemand=PercentagechangeinQPercentagechangeinP0第二十七页，共51页。ELASTICITYANDITSAPPLICATION*PriceElasticityandTotalRevenueElasticdemand(elasticity=1.8)PQD$20012IfP=$200,Q=12andrevenue=$2400.WhenDiselastic,apriceincreasecausesrevenuetofall.0$2508IfP=$250,Q=8andrevenue=$2000.lostrevenueduetolowerQincreasedrevenueduetohigherPDemandforyourwebsites第二十八页，共51页。ELASTICITYANDITSAPPLICATION*PriceElasticityandTotalRevenueIfdemandisinelastic,thenpriceelast.ofdemand<1%changeinQ<%changeinPThefallinrevenuefromlowerQissmallerthantheincreaseinrevenuefromhigherP,sorevenuerises.Inourexample,supposethatQonlyfallsto10(insteadof8)whenyouraiseyourpriceto$250.Revenue=PxQPriceelasticityofdemand=PercentagechangeinQPercentagechangeinP0第二十九页，共51页。ELASTICITYANDITSAPPLICATION*PriceElasticityandTotalRevenueNow,demandisinelastic:elasticity=0.82PQD$20012IfP=$200,Q=12andrevenue=$2400.$25010IfP=$250,Q=10andrevenue=$2500.WhenDisinelastic,apriceincreasecausesrevenuetorise.0lostrevenueduetolowerQincreasedrevenueduetohigherPDemandforyourwebsites第三十页，共51页。A.Pharmaciesraisethepriceofinsulinby10%.Doestotalexpenditureoninsulinriseorfall?B.Asaresultofafarewar,thepriceofaluxurycruisefalls20%.Doesluxurycruisecompanies’totalrevenueriseorfall?ACTIVELEARNING2Elasticityandexpenditure/revenue*第三十一页，共51页。ELASTICITYANDITSAPPLICATION*APPLICATION:DoesDrugInterdictionIncreaseorDecreaseDrug-RelatedCrime?Onesideeffectofillegaldruguseiscrime:Usersoftenturntocrimetofinancetheirhabit.Weexaminetwopoliciesdesignedtoreduceillegaldruguseandseewhateffectstheyhaveondrug-relatedcrime.Forsimplicity,weassumethetotaldollarvalueofdrug-relatedcrimeequalstotalexpenditureondrugs.Demandforillegaldrugsisinelastic,duetoaddictionissues.0第三十二页，共51页。ELASTICITYANDITSAPPLICATION*D1Policy1:Interdiction0PriceofDrugsQuantityofDrugsS1S2P1Q1P2Q2Interdictionreducesthesupplyofdrugs.Sincedemandfordrugsisinelastic,Prisespropor-tionallymorethanQfalls.Result:anincreaseintotalspendingondrugs,andindrug-relatedcrimenewvalueofdrug-relatedcrimeinitialvalueofdrug-relatedcrime第三十三页，共51页。ELASTICITYANDITSAPPLICATION*Policy2:Education0PriceofDrugsQuantityofDrugsD1SP1Q1D2P2Q2Educationreducesthedemandfordrugs.PandQfall.Result:Adecreaseintotalspendingondrugs,andindrug-relatedcrime.initialvalueofdrug-relatedcrimenewvalueofdrug-relatedcrime第三十四页，共51页。ELASTICITYANDITSAPPLICATION*PriceElasticityofSupplyPriceelasticityofsupplymeasureshowmuchQsrespondstoachangeinP.Priceelasticityofsupply=PercentagechangeinQsPercentagechangeinPLooselyspeaking,itmeasuressellers’price-sensitivity.Again,usethemidpointmethodtocomputethepercentagechanges.0第三十五页，共51页。ELASTICITYANDITSAPPLICATION*Q2PriceElasticityofSupplyPriceelasticityofsupplyequals0PQSP2Q1P1Prisesby8%Qrisesby16%16%8%=2.0Priceelasticityofsupply=PercentagechangeinQsPercentagechangeinPExample:第三十六页，共51页。ELASTICITYANDITSAPPLICATION*TheVarietyofSupplyCurvesTheslopeofthesupplycurveiscloselyrelatedtopriceelasticityofsupply.Ruleofthumb:Theflatterthecurve,thebiggertheelasticity.Thesteeperthecurve,thesmallertheelasticity.Fivedifferentclassifications.…0第三十七页，共51页。ELASTICITYANDITSAPPLICATION*S“Perfectlyinelastic”(oneextreme)PQQ1P1P2Qchangesby0%00%10%=0Priceelasticityofsupply=%changeinQ%changeinP=Prisesby10%Sellers’pricesensitivity:Scurve:Elasticity:verticalnone0第三十八页，共51页。ELASTICITYANDITSAPPLICATION*S“Inelastic”PQQ1P1Q2P2Qriseslessthan10%0<10%10%<1Priceelasticityofsupply=%changeinQ%changeinP=Prisesby10%Sellers’pricesensitivity:Scurve:Elasticity:relativelysteeprelativelylow<1第三十九页，共51页。ELASTICITYANDITSAPPLICATION*S“Unitelastic”PQQ1P1Q2P2Qrisesby10%010%10%=1Priceelasticityofsupply=%changeinQ%changeinP=Prisesby10%Sellers’pricesensitivity:Scurve:Elasticity:intermediateslopeintermediate=1第四十页，共51页。ELASTICITYANDITSAPPLICATION*S“Elastic”PQQ1P1Q2P2Qrisesmorethan10%0>10%10%>1Priceelasticityofsupply=%changeinQ%changeinP=Prisesby10%Sellers’pricesensitivity:Scurve:Elasticity:relativelyflatrelativelyhigh>1第四十一页，共51页。ELASTICITYANDITSAPPLICATION*S“Perfectlyelastic”(theotherextreme)PQP1Q1Pchangesby0%Qchangesbyany%0any%0%=infinityPriceelasticityofsupply=%changeinQ%changeinP=Q2P2=Sellers’pricesensitivity:Scurve:Elasticity:horizontalextremeinfinity第四十二页，共51页。ELASTICITYANDITSAPPLICATION*TheDeterminantsofSupplyElasticityThemoreeasilysellerscanchangethequantitytheyproduce,thegreaterthepriceelasticityofsupply.Example:Supplyofbeachfrontpropertyishardertovaryandthuslesselasticthansupplyofnewcars.Formanygoods,priceelasticityofsupplyisgreaterinthelongrunthanintheshortrun,becausefirmscanbuildnewfactories,ornewfirmsmaybeabletoenterthemarket.第四十三页，共51页。ACTIVELEARNING3Elasticityandchangesinequilibrium*Thesupplyofbeachfrontpropertyisinelastic.Thesupplyofnewcarsiselastic.Supposepopulationgrowthcausesdemandforbothgoodstodouble(ateachprice,Qddoubles).ForwhichproductwillPchangethemost?ForwhichproductwillQchangethemost?第四十四页，共51页。ELASTICITYANDITSAPPLICATION*SHowthePriceElasticityofSupplyCanVaryPQ0SupplyoftenbecomeslesselasticasQrises,duetocapacitylimits.$1552512500$31004200elasticity>1elasticity<1第四十五页，共51页。ELASTICITYANDITSAPPLICATION*OtherElasticitiesIncomeelasticityofdemand:measurestheresponseofQdtoachangeinconsumerincomeIncomeelasticityofdemand=PercentchangeinQdPercentchangeinincomeRecallfromChapter4:Anincreaseinincomecausesanincreaseindemandforanormalgood.Hence,fornormalgoods,incomeelasticity>0.Forinferiorgoods,incomeelasticity<0.第四十六页，共51页。ELASTICITYANDITSAPPLICATION*OtherElasticitiesCross-priceelasticityofdemand:measurestheresponseofdemandforonegoodtochangesinthepriceofanothergoodCross-priceelast.ofdemand=%changeinQdforgood1%changeinpriceofgood2Forsubstitutes,cross-priceelasticity>0(e.g.,anincreaseinpriceofbeefcausesanincreaseindemandforchicken)Forcomplements,cross-priceelasticity<0(e.g.,anincreaseinpriceofcomputerscausesdecreaseindemandforsoftware)第四十七页，共51页。ELASTICITYANDITSAPPLICATION*Cross-PriceElasticitiesintheNews“AsGasCostsSoar,BuyersFlocktoSmallCars”-NewYorkTimes,5/2/2008“GasPricesDriveStudentstoOnlineCourses”-ChronicleofHigherEducation,7/8/2008“Gaspricesknockbicyclesales,repairsintohighergear”-AssociatedPress,5/11/2008“CameldemandsoarsinIndia”(asasubstitutefor“gas-guzzlingtractors”)-FinancialTimes,5/2/2008“Highgaspricesdrivefarmertoswitchtomules”-AssociatedPress,5/21/2008第四十八页，共51页。CHAPTERSUMMARYElasticitymeasurestheresponsivenessofQdorQstooneofitsdeterminants.PriceelasticityofdemandequalspercentagechangeinQddividedbypercentagechangeinP.Whenit’slessthanone,demandis“inelastic.”Whengreaterthanone,demandis“elastic.”Whendemandisinelastic,totalrevenueriseswhenpricerises.Whendemandiselastic,totalrevenuefallswhenpricerises.*第四十九页，共51页。CHAPTERSUMMARYDemandislesselasticintheshortrun,fornecessities,forbroadlydefinedgoods,orforgoodswithfewclosesubstitutes.PriceelasticityofsupplyequalspercentagechangeinQsdividedbypercentagechangeinP.Whenit’slessthanone,supplyis“inelastic.”Whengreaterthanone,supplyis“elastic.”Priceelasticityofsupplyisgreaterinthelongrunthanintheshortrun.*第五十页，共51页。CHAPTERSUMMARYTheincomeelasticityofdemandmeasureshowmuchquantitydemandedrespondstochangesinbuyers’incomes.Thecross-priceelasticityofdemandmeasureshowmuchdemandforonegoodrespondstochangesinthepriceofanothergood.*第五十一页，共51页。