曼昆经济学 宏观经济学 第五版 教师参考手册 chap05.docx
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曼昆经济学 宏观经济学 第五版 教师参考手册 chap05.docx
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曼昆经济学宏观经济学第五版教师参考手册chap05
5
ELASTICITYANDITSAPPLICATION
WHAT’SNEW:
Thediscussionof“TheMidpointFormula”and“ElasticityAlongaLinearDemandCurve”arenowpartofthemaintext.Thecross-priceelasticityofdemandisalsonowincludedinthischapter.
LEARNINGOBJECTIVES:
Bytheendofthischapter,studentsshouldunderstand:
Øthemeaningoftheelasticityofdemand.
Øwhatdeterminestheelasticityofdemand.
Øthemeaningoftheelasticityofsupply.
Øwhatdeterminestheelasticityofsupply.
Øtheconceptofelasticityinthreeverydifferentmarkets(themarketforwheat,themarketforoil,andthemarketforillegaldrugs).
KEYPOINTS:
1.Thepriceelasticityofdemandmeasureshowmuchthequantitydemandedrespondstochangesintheprice.Demandtendstobemoreelasticifthegoodisaluxuryratherthananecessity,ifclosesubstitutesareavailable,ifthemarketisnarrowlydefined,orifbuyershavesubstantialtimetoreacttoapricechange.
2.Thepriceelasticityofdemandiscalculatedasthepercentagechangeinquantitydemandeddividedbythepercentagechangeinprice.Iftheelasticityislessthanone,sothatquantitydemandedmovesproportionatelylessthantheprice,demandissaidtobeinelastic.Iftheelasticityisgreaterthanone,sothatquantitydemandedmovesproportionatelymorethantheprice,demandissaidtobeelastic.
3.Totalrevenue,thetotalamountpaidforagood,equalsthepriceofthegoodtimesthequantitysold.Forinelasticdemandcurves,totalrevenuerisesaspricerises.Forelasticdemandcurves,totalrevenuefallsaspricerises.
4.Theincomeelasticityofdemandmeasureshowmuchthequantitydemandedrespondstochangesinconsumers’income.Thecross-priceelasticityofdemandmeasureshowmuchthequantitydemandedofonegoodrespondstothepriceofanothergood.
5.Thepriceelasticityofsupplymeasureshowmuchthequantitysuppliedrespondstochangesintheprice.Thiselasticityoftendependsonthetimehorizonunderconsideration.Inmostmarkets,supplyismoreelasticinthelongrunthanintheshortrun.
6.Thepriceelasticityofsupplyiscalculatedasthepercentagechangeinquantitysupplieddividedbythepercentagechangeinprice.Iftheelasticityislessthanone,sothatquantitysuppliedmovesproportionatelylessthantheprice,supplyissaidtobeinelastic.Iftheelasticityisgreaterthanone,sothatquantitysuppliedmovesproportionatelymorethantheprice,supplyissaidtobeelastic.
7.Thetoolsofsupplyanddemandcanbeappliedinmanydifferentkindsofmarkets.Thischapterusesthemtoanalyzethemarketforwheat,themarketforoil,andthemarketforillegaldrugs.
CHAPTEROUTLINE:
I.TheElasticityofDemand
A.DefinitionofElasticity:
ameasureoftheresponsivenessofquantitydemandedorquantitysuppliedtooneofitsdeterminants.
B.ThePriceElasticityofDemandandItsDeterminants
1.DefinitionofPriceElasticityofDemand:
ameasureofhowmuchthequantitydemandedofagoodrespondstoachangeinthepriceofthatgood,computedasthepercentagechangeinquantitydemandeddividedbythepercentagechangeinprice.
2.DeterminantsofPriceElasticityofDemand
a.NecessitiesversusLuxuries:
necessitiesaremorepriceinelastic.
b.AvailabilityofCloseSubstitutes:
themoresubstitutesagoodhas,themoreelasticitsdemand.
c.DefinitionoftheMarket:
narrowlydefinedmarkets(icecream)havemoreelasticdemandthanbroadlydefinedmarkets(food).
d.TimeHorizon:
goodstendtohavemoreelasticdemandoverlongertimehorizons.
C.ComputingthePriceElasticityofDemand
1.Formula
Workthroughacoupleofelasticitycalculations,startingwiththeexampleinthebook.Forprinciplesofeconomicscourseswherethereisnomathematicalprerequisite,thismaybedifficultforsomestudents.Doingacoupleofsimpleexampleswillhelptoalleviatesomeofthestudents’anxiety.Showeverystepofthealgebrainvolved.
2.Example:
priceoficecreamrisesby10%andquantitydemandedfallsby20%.
Priceelasticityofdemand=(20%)/(10%)=2
3.Becausethereisaninverserelationshipbetweenpriceandquantitydemanded(thepriceoficecreamroseby10%andthequantitydemandedfellby20%),thepriceelasticityofdemandissometimesreportedasanegativenumber.Wewillignoretheminussignandconcentrateontheabsolutevalueoftheelasticity.
Studentshatethis!
Iftheypressyou,explainthatitreallymakesthingseasierandmakesmoresensebecauselargerelasticities(inabsolutevalue)implygreatersensitivityandresponsiveness.
D.TheMidpointMethod:
ABetterWaytoCalculatePercentageChangesandElasticities
1.Becauseweusepercentagechangesincalculatingthepriceelasticityofdemand,theelasticitycalculatedbygoingfrompointAtopointBonademandcurvewillbedifferentthananelasticitycalculatedbygoingfrompointBtopointA.
a.Awayaroundthisiscalledthemidpointmethod.
b.Usingthemidpointmethodinvolvescalculatingthepercentagechangeineitherpriceorquantitydemandedbydividingthechangeinthevariablebythemidpointbetweentheinitialandfinallevelsratherthanbytheinitiallevelitself.
c.Example:
pricerisesfrom$4to$6.
%changeinprice=(6-4)/5×100%=40%
E.TheVarietyofDemandCurves
Figure5-1
1.ClassificationofElasticity
a.Whentheelasticityisgreaterthanone,thedemandisconsideredtobeelastic.
b.Whentheelasticityislessthanone,thedemandisconsideredtobeinelastic.
c.
ALTERNATIVECLASSROOMEXAMPLE:
Thepriceofacompactdiscplayerrisesfrom$100to$150,whilethequantitydemandedfallsfrom1200to900.
Tocalculatethepriceelasticityofdemand,weusethemidpointformulatocalculatethe%changeinquantitydemandedandthe%changeinprice:
%changeinquantitydemanded=(1200–900)/1050=.2857=28.57%
%changeinprice=(150–100)/125=.40=40%
Thepriceelasticityofdemandisequalto:
%changeinquantitydemanded/%changeinprice=28.57/40=0.71
Giventhisinformation,youcannow:
▪classifythedemandaselastic,inelasticorunitelastic.
▪calculatetotalrevenuebothbeforeandafterthepricechange.
▪calculatethepercentagechangeinquantitydemandedifpricewastoriseanother5%(usingthepriceelasticityofdemandtheycalculated).
▪calculatethepercentagechangeinpriceneededtoincreasequantitydemandedby25%(usingthepriceelasticityofdemandtheycalculated).
Whentheelasticityisequaltoone,thedemandiscalledunitelastic.
InelasticDemand
Price
ElasticDemand
Quantity
2.SlopeofDemandCurve:
ingeneral,theflatterthedemandcurvethemoreelasticthedemand.
Price
Price
PerfectlyInelasticDemand
PerfectlyElasticDemand
Quantity
Quantity
Makesurethatyouprovideseveralexamplesofgoodswiththesetypesofdemandcurves.Youmaywanttopointoutthatstudentswillseetheperfectlyelasticdemandcurveagainwhencompetitivefirmsarediscussed.
3.ExtremeCases
a.Whentheelasticityisequaltozero,thedemandisperfectlyinelasticandisaverticalline.
b.Whentheelasticityisinfinite,thedemandisperfectlyelasticandisahorizontalline.
F.TotalRevenueandthePriceElasticityofDemand
Figure5-2
2.DefinitionofTotalRevenue:
theamountpaidbybuyersandreceivedbysellersofagood,computedasthepriceofthegoodtimesthequantitysold.
Anothertermforpricetimesquantityis“totalexpenditure.”Thistermissometimesusedinquestionsfoundinthestudyguideandtestbank.Itisalsoimportanttopointthisoutwhendiscussingthe“illegaldrug”exampleattheendofthechapter.
Studentsfindtherelationshipbetweenchangesintotalrevenueandelasticitydifficulttounderstand.Itmaytakeseveralthoroughdiscussionsofthismaterialbeforestudentswillbeabletomasterit.
2.Ifdemandisinelastic,thechangeinpricewillbegreaterthanthechangeinquantitydemanded.
Figure5-3
a.Ifpricerises,quantitydemandedfalls,andtotalrevenuewillrise(becausetheincreaseinpricewaslargerthanthedecreaseinquantitydemanded).
b.Ifpricefalls,quantitydemandedrises,andtotalrevenuewillfall(becausethefallinpricewaslargerthantheincreaseinquantitydemanded).
3.Ifdemandiselastic,thechangeinquantitydemandedwillbegreaterthanthechangeinprice.
Figure5-4
a.Ifpricerises,quantitydemandedfalls,andtotalrevenuewillfall(becausetheincreaseinpricewassmallerthanthedecreaseinquantitydemanded).
b.Ifpricefalls,quantitydemandedrises,andtotalrevenuewillrise(becausethefallinpricewassmallerthantheincreaseinquantitydemanded).
4.Ifdemandisunitelastic,thechangeinpricewillbeequaltothechangeinquantitydemanded.
a.Ifpricerises,quantitydemandedfalls,andtotalrevenuewillremainthesame(becausetheincreaseinpricewasequaltothedecreaseinquantitydemanded).
b.Ifpricefalls,quantitydemandedrises,andtotalrevenuewillremainthesame(becausethefallinpricewasequaltotheincreaseinquantitydemanded).
Pointouttheusefulnessofelasticityfromabusinessowner’spointofview.Studentsshouldbeabletoseewhyafirmmanagerwillwanttoknowtheelasticityofdemandforthefirm.
G.ElasticityandTotalRevenueAlongaLinearDemandCurve
Figure5-5
Table5-1
1.Theslopeofalineardemandcurveisconstant,buttheelasticityisnot.
a.Atpointswithalowpriceandahighquantity,demandisinelastic.
b.Atpointswithahighpriceandalowquantity,demandiselastic.
2.
Notethat,whendemandiselasticandpricefalls,totalrevenuerises.Alsopointout
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