個(gè)人與市場(chǎng)需求

IndividualandMarketDemand個(gè)人與市場(chǎng)需求目錄1.1個(gè)人需求線的導(dǎo)出1.2所得與替代效果1.3市場(chǎng)需求1.4消費(fèi)者剩余1.5網(wǎng)絡(luò)外部性1.6實(shí)證研究1.1從無(wú)異曲線導(dǎo)出需求線某物的『價(jià)格』改變預(yù)算線變動(dòng)與不同的無(wú)異曲線相切切點(diǎn)對(duì)應(yīng)的,即是該物的『需求量』『價(jià)格』與『需求量』的關(guān)系=需求線EffectofaPriceChangeFood(unitspermonth)Clothing(unitspermonth)456U2U3ABDU141220三條無(wú)異曲線(滿足.IC.特性)三個(gè)切點(diǎn)Assume:I=$20PC=$2PF=$2,$1,$.5010Price-ConsumptionCurveEffectofaPriceChangeFood(unitspermonth)Clothing(unitspermonth)456U2U3ABDU141220價(jià)格消費(fèi)線Price-ConsumptionCurveEffectofaPriceChangeDemandCurvePF

與QF

的關(guān)系,就是F的需求線Food(unitspermonth)PriceofFoodHEG$2.0041220$1.00$.50PFQF$24$112$.520需求線需求在線的不同點(diǎn),效用水平不同

(看前面的圖,PF下跌,效用提高)需求線各點(diǎn),都是效用最大點(diǎn):對(duì)應(yīng)不同的條件,都是MRS=價(jià)格比

(看下圖)需求線的兩大特性價(jià)格變動(dòng),導(dǎo)出需求線Food(unitspermonth)PriceofFoodHEG$2.0041220$1.00$.50DemandCurveE:Pf/Pc=2/2=1=MRSG:Pf/Pc=1/2=.5=MRSH:Pf/Pc=.5/2=.25=MRS當(dāng)F的價(jià)格下降,Pf/Pc

下降,MRS也跟著下降需求價(jià)格需求在線每一點(diǎn),都是

MUF/MUC=PF/PC也就是:(用貨幣代替C)

MUF/MUM=PFMBF=PF,邊際效益=邊際效用的貨幣值亦即需求價(jià)格,消費(fèi)者愿付的最高價(jià)格需求價(jià)格－實(shí)際支付=消費(fèi)者剩余所得變動(dòng)所得增加預(yù)算線平行外移與較高的無(wú)異曲線相切形成所得消費(fèi)線

(IncomeConsumtioncurve)所得變動(dòng)

所得消費(fèi)線Food(unitspermonth)Clothing(unitspermonth)假設(shè)兩物都是正常財(cái)?shù)腎CC(正斜率,不一定直線)Income-ConsumptionCurve34AU1510BU2D716U3Assume:Pf=$1 Pc=$2

I=$10,$20,$30所得變動(dòng),需求線移動(dòng)Food(unitspermonth)Priceoffood價(jià)格不動(dòng),所得增加(from$10to$20to$30),需求線外移$1.004D1E10D2G16D3H所得改變?nèi)绻鸌CC正斜率,則兩物都是正常財(cái):(兩物)需求的所得彈性均為正若ICC后彎成負(fù)斜率,則橫軸是劣等財(cái)該物需求的所得彈性為負(fù)若ICC前曲成負(fù)斜率,則縱軸是劣等財(cái)該物需求的所得彈性為負(fù)正常財(cái)(normalgoods)劣等財(cái)(inferiorgoods)H物品由正常財(cái)轉(zhuǎn)變成劣等財(cái)Hamburger(unitspermonth)Steak(unitspermonth)1530U3CIncome-ConsumptionCurveBC階段,H由正常財(cái)

變成劣等財(cái)10520510AU1BU2AB階段,兩物均為正常財(cái)縱軸為劣等財(cái)由此可證，兩物模型中，不可能兩物皆為劣等財(cái)Steak(unitspermonth)Hamburger(unitspermonth)所得變動(dòng)恩格爾曲線(EngelCurves)1)所得(縱軸)與消費(fèi)量(橫軸)的關(guān)系2)TheEngelcurve斜率正,正常財(cái)3)TheEngelcurve斜率負(fù),劣等財(cái)EngelCurves(注意兩軸)Food(unitspermonth)30481210Income($permonth)20160正常財(cái)EngelCurves恩格爾曲線一物是正常財(cái)或

劣等財(cái),因人,因時(shí),因地而異,沒(méi)有定性劣等財(cái)正常財(cái)Food(unitspermonth)30481210Income($permonth)20160美國(guó)的消費(fèi)支出娛樂(lè) 700 947 1274 1514 2054 2654 4300自有房屋 1116 1725 2253 3243 4454 5793 9898租屋 1957 2170 2371 2536 2137 1540 1266健康 1031 1697 1918 1820 2052 2214 2642食物 2656 3385 4109 4888 5429 6220 8279衣著 859 978 1363 1772 1778 2614 3442 Lessthan 1,000- 20,000- 30,000- 40,000- 50,000- 70,000-支出項(xiàng)目 $10,000 19,000 29,000 39,000 49,000 69,000 andabove所得組群劣等財(cái)必需品必需品美國(guó)家庭的年消費(fèi)支出(醫(yī)療)(租屋)(娛樂(lè))Chapter4Slide21租屋娛樂(lè)醫(yī)療臺(tái)灣家庭收支調(diào)查五等分位可支配所得292,113538,584743,8881,005,2741,799,733保健醫(yī)療支出47,07166,02483,06596,023120,951房租及水費(fèi)支出81,770116,452132,553158,654212,351娛樂(lè)及文化支出23,72657,77384,559113,960174,575煙草支出4,1256,1566,7247,3996,6642002臺(tái)灣家庭收支調(diào)查表6臺(tái)灣的恩格爾曲線臺(tái)灣的恩格爾曲線另一物的價(jià)格變動(dòng)一物價(jià)格升,另一物需求增

替代品e.g.movieticketsandvideorentals一物價(jià)格升,另一物需求減互補(bǔ)品e.g.gasolineandmotoroil一物價(jià)格變動(dòng)不改變另一物需求

(兩物之間為)獨(dú)立品(independent)Substitutes替代品vs.Complements互補(bǔ)品替代品與互補(bǔ)品如果價(jià)格消費(fèi)線(PCC)是負(fù)斜率,

兩物為替代品如果價(jià)格消費(fèi)線(PCC)是正斜率,

兩物為互補(bǔ)品1.2所得與替代效果

IncomeandSubstitutionEffects價(jià)格效果=替代效果+所得效果替代效果:用較便宜替代較貴的所得效果:一物降價(jià),消費(fèi)者購(gòu)買力增

(購(gòu)買力=實(shí)質(zhì)所得)無(wú)異曲線圖上的所得與替代效果替代效果(SubstitutionEffect)

1.替代效果是效用維持不變下,一物價(jià)格變動(dòng)造成的消費(fèi)改變.2.

當(dāng)價(jià)格下跌,替代效果是使需求量增加.無(wú)異曲線圖上的所得與替代效果所得效果(IncomeEffect)

1.所得效果

是價(jià)格不變下,所得增加引起消費(fèi)改變的效果.

2.

當(dāng)所得增加,所得效果可能使需求量增加(正常財(cái)),也可能減少(劣等財(cái)).3.劣等財(cái)?shù)男Ч?通常小于替代效果;換言之,GiffenGoods很少可能.正常財(cái)(NormalGood)Food(unitspermonth)OClothing(unitspermonth)RF1SC1AU1剩下的

EF2

就是所得效果(即從D點(diǎn)到B點(diǎn)),因?yàn)檫@是維持相對(duì)價(jià)格不變,但改變(此處為增加)購(gòu)買力.IncomeEffectC2F2TU2B當(dāng)F的價(jià)格下跌,消費(fèi)者增加F的消費(fèi)量F1F2,即從A點(diǎn)到

B點(diǎn).ETotalEffectSubstitutionEffectD如果把實(shí)質(zhì)所得(即,滿足程度)固定,單純改變價(jià)格,即得到替代效果

F1E(即從A點(diǎn)到D點(diǎn)).Food(unitspermonth)ORClothing(unitspermonth)F1SF2TAU1ESubstitutionEffectDTotalEffectPF下跌,如F是劣等財(cái),所得效果(EF2)會(huì)使QF

減少.但是,這里(通常)替代效果大于所得效果(F1E>EF2).BIncomeEffectU2劣等財(cái)(InferiorGood)Food(unitspermonth)ORClothing(unitspermonth)F1SF2TAU1ESubstitutionEffectD季芬財(cái)(GiffenGood)當(dāng)劣等財(cái)?shù)乃眯Ч?EF2,即從D點(diǎn)到B點(diǎn))大于替代效果(F1E,即從Q點(diǎn)到B點(diǎn)),就稱為季芬財(cái).BIncomeEffect季芬財(cái)(GiffenGood)需求法則的例外1.理論上,負(fù)的所得效果可能大于

替代效果,使需求線成為正斜率.2.但實(shí)際上,這很少發(fā)生.只有當(dāng)那劣等財(cái)是必需品,而且消耗了消費(fèi)者絕大部分的所得時(shí),才可能.3.例如,I=$100,甘藷價(jià)格=$0.6時(shí),消費(fèi)$60,米消費(fèi)$20(其余消費(fèi)$20),現(xiàn)在漲為$0.65.例子:汽油稅效果,退稅(Rebate)AssumePed=-0.5Income=$9,000Priceofgasoline=$1退稅900加侖x

$0.5=$450(要$600才能回到1200)所得彈性=0.3汽油消費(fèi)增加900x(0.3x5=1.5)=13.5EffectofaGasolineTaxWithaRebateGasolineConsumption(gallons/year)

ExpendituresOnOtherGoods($)ACGasoline=1200gallonsOtherexpenditures=$7800U21200OriginalBudgetLineBDU1900AfterGasolineTaxE$.50ExciseTaxGasoline=900gallonsJFH913.5AfterGasolineTaxPlusRebateU3$450REBATENewbudgetlineConsumerisworseoff1.3市場(chǎng)需求

MarketDemand市場(chǎng)需求線水平加總個(gè)人需求線,得到市場(chǎng)需求線,

(因?yàn)閿?shù)量在橫軸).隨時(shí)消費(fèi)者人數(shù)增加,市場(chǎng)需求線右移從個(gè)人需求到市場(chǎng)需求Determiningthe

MarketDemandCurve1 6 10 16 322 4 8 13 253 2 6 10 184 0 4 7 115 0 2 4 6

Price IndividualA IndividualB IndividualC Market ($) (units) (units) (units) (units)SummingtoObtaina

MarketDemandCurveQuantity1234Price0551015202530DBDCMarketDemandDA水平加總個(gè)人需求線即得市場(chǎng)需求線MarketDemand需求彈性.需求彈性需求彈性>1Ep

大于1(絕對(duì)值)時(shí),數(shù)量變動(dòng)大于價(jià)格%Q>%P因此,總支出(賣方之總收益,PQ)將因價(jià)格提高而降低(因?yàn)镻與Q反向變動(dòng))相反,若彈性小于1,則PQ與P同向變動(dòng)若彈性=1,則P變動(dòng)時(shí),PQ不變需求彈性與總支出

當(dāng)價(jià)格提高, 當(dāng)價(jià)格下降,

彈性 總支出: 總支出:Inelastic(Ep

<1)

增加

減少UnitElastic(Ep=1) 不變

不變Elastic(Ep>1) 減少

增加MarketDemand點(diǎn)彈性(Pointelasticity)MarketDemand點(diǎn)彈性的問(wèn)題當(dāng)實(shí)際價(jià)格變動(dòng)時(shí),計(jì)算點(diǎn)彈性會(huì)有起始點(diǎn)的問(wèn)題.用變動(dòng)前或變動(dòng)后為分母,計(jì)算結(jié)果不同.MarketDemandAssume價(jià)格從8$上升到$10,需求量從6減為4價(jià)格變動(dòng)百分比:$2/$8=25%or$2/$10=20%數(shù)量變動(dòng)百分比:-2/6=-33.33%or-2/4=-50%需求彈性哪個(gè)對(duì)? -33.33/.25=-1.33or-.50/.20=-2.54點(diǎn)彈性(例子)MarketDemand弧彈性(Arcelasticity)MarketDemand弧彈性(AnExample)TheAggregateDemandForWheatThedemandforU.S.wheatiscomprisedofdomesticdemandandexportdemand.市場(chǎng)需求線AnExample:TheAggregateDemandForWheatThedomesticdemandforwheatisgivenbytheequation:QDD=1,465-88PTheexportdemandforwheatisgivenbytheequation:QDE=1344-138PTheAggregateDemandForWheatDomesticdemandisrelativelypriceinelastic(-0.2),whileexportdemandismorepriceelastic(-0.4).CDExportDemandABDomesticDemandTotalworlddemandisthehorizontalsumofthedomesticdemandABandexportdemandCD.FTotalDemandETheAggregateDemandForWheatWheat(millionbushels/yr.)Price

($/bushel)024681012141618201000200030004000Q=2809-226PforEF1.4消費(fèi)者剩余

ConsumerSurplus消費(fèi)者剩余(ConsumerSurplus)

消費(fèi)者最高愿意支出,超過(guò)實(shí)際支出的差額,就是消費(fèi)者剩余.需求在線的價(jià)格,即需求價(jià)格,也就是

消費(fèi)者愿付之最高價(jià)格Theconsumersurplusofpurchasing6concertticketsisthesumofthesurplusderivedfromeachoneindividually.

ConsumerSurplus6+5+4+3+2+1=21ConsumerSurplusRockConcertTicketsPrice

($perticket)23456130114151617181920MarketPriceConsumerSurplus如果變動(dòng)的單位量減少,階梯狀的需求線會(huì)慢慢變成連續(xù)的.DemandCurveConsumerSurplusActualExpenditureConsumerSurplusfortheMarketDemandConsumerSurplusRockConcertTicketsPrice

($perticket)23456130114151617181920MarketPriceConsumerSurplus結(jié)合消費(fèi)者剩余與生產(chǎn)者的利潤(rùn),可以知道: 1) 不同市場(chǎng)結(jié)構(gòu)的成本效益 2) 公共政策如何改變消費(fèi)者與廠商的行為清潔空氣的價(jià)值A(chǔ)irisfreeinthesensethatwedon’tpaytobreatheit.TheCleanAirActwasamendedin1970.Question:Werethebenefitsofcleaninguptheairworththecosts?例子:TheValueofCleanAirPeoplepaymoretobuyhouseswheretheairisclean.DataforhousepricesamongneighborhoodsofBostonandLosAngeleswerecomparedwiththevariousairpollutants.Theshadedareagivestheconsumersurplusgeneratedwhenairpollutionisreducedby5partsper100millionofnitrousoxide(亞硝酸氧化物)

atacostof$1000perpartreduced.ValuingCleanerAir200010010005ANOX(pphm)PollutionReductionValue($perpphmofreduction)1.5網(wǎng)絡(luò)外部性

NetworkExternalities以上我們假設(shè)消費(fèi)者之間相互獨(dú)立,即各自效用互不影響.實(shí)際上,

消費(fèi)者之間的需求是有互動(dòng)關(guān)系的,即別人的消費(fèi)會(huì)影響您的購(gòu)買量這時(shí),我們就稱之為網(wǎng)絡(luò)外部性網(wǎng)絡(luò)外部性有正有負(fù)網(wǎng)絡(luò)外部性

(NetworkExternalities)正的網(wǎng)絡(luò)外部性(positivenetworkexternality)是當(dāng)別人消費(fèi)增加時(shí),您的消費(fèi)會(huì)跟著增加.負(fù)的網(wǎng)絡(luò)外部性(negativenetworkexternalities)相反.網(wǎng)絡(luò)外部性

(NetworkExternalities)隨波逐流效果(TheBandwagonEffect;西瓜偎大邊;同儕效應(yīng))喜歡跟別人一樣,或追求時(shí)尚.這通常是營(yíng)銷(marketing)或廣告(advertising)的目的(e.g.toys,clothing,葡式蛋塔;電子雞;電子娃娃;……).正的網(wǎng)絡(luò)外部性:BandwagonEffectQuantity

(thousandspermonth)Price($perunit)D202040Whenconsumersbelievemorepeoplehavepurchasedtheproduct,thedemandcurveshiftsfurthertothetheright.D4060D6080D80100D100Demand正的網(wǎng)絡(luò)外部性:BandwagonEffectQuantity

(thousandspermonth)Price($perunit)D2020406080100D40D60D80D100Themarketdemandcurveisfoundbyjoiningthepointsontheindividualdemandcurves.Itisrelativelymoreelastic.Demand正的網(wǎng)絡(luò)外部性:BandwagonEffectQuantity

(thousandspermonth)Price($perunit)D2020406080100D40D60D80D100PurePriceEffect48假設(shè)價(jià)格從$30降到$20.如果沒(méi)有同儕效應(yīng),

需求量將只增加到48$20$30Demand正的網(wǎng)絡(luò)外部性:BandwagonEffectQuantity

(thousandspermonth)Price($perunit)D2020406080100D40D60D80D100PurePriceEffect$2048BandwagonEffect但是,當(dāng)消費(fèi)者人數(shù)增加,它會(huì)變成流行時(shí)尚,造成需求增加(需求線右移),以致需求量倍增的同儕效果.$30網(wǎng)絡(luò)外部性(NetworkExternalities)特立獨(dú)行效果(TheSnobEffect;標(biāo)新立異效果;叛逆效應(yīng)