第三講 需求理論

第三講需求理論

需求需要作為既定或事實(shí)，不作道德判斷。需要的相對(duì)性：需要導(dǎo)致資源配置，一種需要是為了更多的需要；全部需要滿足是不可能的（最低生活標(biāo)準(zhǔn)的制定，“科學(xué)”與主觀）。稀缺導(dǎo)致需要滿足先后的權(quán)衡。與欲望（desire）區(qū)別需求表與需求量：價(jià)格上升因而需求減少？需求增加因而價(jià)格上升？需求曲線：PoQD需求曲線與時(shí)間橫軸的時(shí)間段瞬間快照長期、中期與短期彈性需求定律Thelawofdemand:價(jià)格下降，需求量上升需求定律在經(jīng)濟(jì)學(xué)中的地位。價(jià)重新定義使用價(jià)值交換價(jià)值鉆石與水的悖論沒有市場價(jià)，“替代”概念現(xiàn)值的價(jià)量成交量與需求量有質(zhì)的量與委托的量（市場區(qū)分）價(jià)與量的對(duì)應(yīng)消費(fèi)者剩余什么是消費(fèi)者剩余五個(gè)蘋果最高用值30（10+8+6+4+2），總換值10（2×5），消費(fèi)者剩余20三種收費(fèi)辦法：單獨(dú)定價(jià)；入場費(fèi)或兩部定價(jià)；全部或零其他情況不變Otherthingsequalorunchanged或ceterisparibus其他商品的價(jià)格（互補(bǔ)品和替代品）；收入；偏好參看弗里德曼《價(jià)格理論》第二章和張五常《經(jīng)濟(jì)解釋》第一卷偏好不變的假設(shè)品味的變化。學(xué)術(shù)分工，品味來源及其變化留給心理學(xué)力求證偽的可能性統(tǒng)計(jì)上的需求曲線

例證穿著打扮周末經(jīng)濟(jì)、假日經(jīng)濟(jì)生命與健康的選擇犯罪與懲罰Alchian的蘋果向上傾斜的需求曲線？價(jià)格越貴越有人買？價(jià)格與質(zhì)量；炫耀品；投機(jī)預(yù)期效用什么是效用？邊沁：效用是快樂或享受的指數(shù)。人們追求指數(shù)最大。收入的邊際效用遞減。Stilger縱論悲哀的效用理論發(fā)展。帕累托和費(fèi)雪的貢獻(xiàn)。效用是選擇的序數(shù)排列。其量度可以是任何東西（數(shù)字的三種用途）。痛苦與快樂的計(jì)較？無差異曲線替代定理（“替代”概念在經(jīng)濟(jì)學(xué)中的重要性）內(nèi)凸定理（多樣化）不相交U1CombinationB,A,&DyieldthesamesatisfactionEispreferredtoU1U1

ispreferredtoH&GConsumerPreferencesFood(unitsperweek)1020304010203040Clothing(unitsperweek)50GDAEHB預(yù)算約束瓦爾拉斯預(yù)算集瓦爾拉斯定律預(yù)算集的決定及其變化BudgetLineF+2C=$801020(I/PC)=40BudgetConstraintsFood(unitsperweek)406080=(I/PF)201020300ABDEGClothing(unitsperweek)Pc

=$2Pf=$1I=$80EffectofaPriceChangeFood(unitspermonth)Clothing(unitspermonth)456U2U3ABDU141220Threeseparateindifferencecurvesaretangenttoeachbudgetline.Assume:I=$20PC=$2PF

=$2,$1,$.5010Price-ConsumptionCurveEffectofaPriceChangeFood(unitspermonth)Clothing(unitspermonth)456U2U3ABDU141220Theprice-consumptioncurvetracesouttheutilitymaximizingmarketbasketforthevariouspricesforfood.EffectofaPriceChangeDemandCurveIndividualDemandrelatesthequantityofagoodthataconsumerwillbuytothepriceofthatgood.Food(unitspermonth)PriceofFoodHEG$2.0041220$1.00$.50EffectsofIncomeChangesFood(unitspermonth)Clothing(unitspermonth)Anincreaseinincome,withthepricesfixed,causesconsumerstoaltertheirchoiceofmarketbasket.Income-ConsumptionCurve34AU1510BU2D716U3Assume:Pf=$1

Pc=$2

I=$10,$20,$30EffectsofIncomeChangesFood(unitspermonth)PriceoffoodAnincreaseinincome,from$10to$20to$30,withthepricesfixed,shiftstheconsumer’sdemandcurvetotheright.$1.004D1E10D2G16D3HAnInferiorGoodHamburger(unitspermonth)Steak(unitspermonth)1530U3CIncome-ConsumptionCurve…buthamburgerbecomesaninferiorgoodwhentheincomeconsumptioncurvebendsbackwardbetweenBandC.10520510AU1BU2Bothhamburgerandsteakbehaveasanormalgood,betweenAandB...EngelCurvesFood(unitspermonth)30481210Income($permonth)20160Engelcurvesslopeupwardfornormalgoods.EngelCurvesEngelcurvesslopebackwardbendingforinferiorgoods.InferiorNormalFood(unitspermonth)30481210Income($permonth)20160IncomeandSubstitution

Effects:NormalGoodFood(unitspermonth)OClothing(unitspermonth)RF1SC1AU1Theincomeeffect,EF2,(fromDtoB)keepsrelativepricesconstantbutincreasespurchasingpower.IncomeEffectC2F2TU2BWhenthepriceoffoodfalls,consumptionincreasesbyF1F2

astheconsumermovesfromAtoB.ETotalEffectSubstitutionEffectDThesubstitutioneffect,F1E,(frompointAtoD),changestherelativepricesbutkeepsrealincome(satisfaction)constant.Food(unitspermonth)ORClothing(unitspermonth)F1SF2TAU1ESubstitutionEffectDTotalEffectSincefoodisaninferiorgood,theincomeeffectisnegative.However,thesubstitutioneffectislargerthantheincomeeffect.BIncomeEffectU2IncomeandSubstitution

Effects:InferiorGood從無差異曲線到需求曲線收入效應(yīng)正常物品與貧窮物品（inferiorgoods）吉芬物品的悖論爭論：吉芬物品是否實(shí)際存在放棄效用理論？三種需求曲線馬歇爾需求曲線希克斯需求曲線斯