1、需求與消費(fèi)者行為,第5章,.,選擇和效用理論,5.1,.,3,效用和消費(fèi)者行為,Utility denotes satisfaction. More precisely, it refers to how consumers rank different goods and services. In the theory of demand, we say that people maximize their utility, which means that they choose the bundle of consumption goods (消費(fèi)品束) that they most p

2、refer.,.,背景知識：邊際革命,1870s前期，英國的杰文斯、僑居瑞士的法國人瓦爾拉和奧地利的門格爾，三人發(fā)起“邊際革命”。,4,Lon Walras 1834-1910,Carl Menger 1840-1921,William S. Jevons 1835-1882,.,5,邊際效用價(jià)值論,掀起邊際革命的學(xué)者用倡導(dǎo)并發(fā)揚(yáng)“邊際效用價(jià)值論”，用主觀效用價(jià)值論與當(dāng)時(shí)的勞動(dòng)價(jià)值論相對抗，以邊際分析方法取代當(dāng)時(shí)的平均分析方法，因而成為現(xiàn)代新古典經(jīng)濟(jì)學(xué)的創(chuàng)始人。 Marginal utility denotes the additional utility you get from the c

3、onsumption of an additional unit of a commodity,.,總效用和邊際效用,6,4,3,2,1,0,.,總效用和邊際效用的關(guān)系,7,Total utility,Quantity,O,U,Q,.,邊際效用遞減定律,隨著一種物品的消費(fèi)數(shù)量的增加，最后增加的物品的邊際效用會(huì)不斷減少。,8,Marginal utility,Quantity,O,MU,Q,.,9,序數(shù)效用,An ordinal (序數(shù)) measure simply ranks goods relative to one another. You can say you like peas b

4、etter than broccoli (花椰菜) and you like ice cream better than both of those vegetables, but you dont really need to say how much to rank your preferences (偏好) for these goods.,.,10,背景知識,用序數(shù)效用論取代基數(shù)效用論的原因有二： 對于一些不可缺少的物品的效用，基數(shù)論可能給出不合理的結(jié)果。 序數(shù)效用論比基數(shù)效用論需要的假設(shè)更少，所需的假設(shè)也更簡單。,.,需求曲線的推導(dǎo),5.2,.,消費(fèi)者的最優(yōu)化,我們假定每個(gè)消費(fèi)者最大

5、化其效用，我們還假定消費(fèi)者的收入是給定的，并面對給定的市場價(jià)格。 問題：當(dāng)你的預(yù)算給定時(shí)，如何在不同的物品和服務(wù)中分配支出，達(dá)到的滿意度最大？,12,基數(shù)效用的說明,.,13,等邊際原理,Equimarginal principle: A consumer will achieve maximum satisfaction or utility when the marginal utility of the last dollar spent on a good is exactly the same as the marginal utility of the last dollar sp

6、ent on any other good. This is the utility-maximizing rule or the equimarginal principle (效用最大化準(zhǔn)則或等邊際原理).,.,等邊際原理的通俗解釋,如果在收入的各項(xiàng)支出中，從任一支出中拿出一元錢放到其他的支出中，都不會(huì)使（總）效用增加，那么原來的支出配置達(dá)到最好。,14,.,為什么需求曲線向下傾斜,The equimarginal principle perfectly explains why demand curves slope downward.,15,MU,Price,保持 不變,.,測試問題,

7、Try to fill the empty boxes correctly with either an equals sign, a greater than sign, or a less than sign.,16, =, =,consume more of good X,consume more of good Z,.,正確的回答,金錢從最后1元錢帶來的效用小的地方移向效用大的地方，能夠增加總效用。,17,consume more of good X,consume more of good Z,.,閑暇和最優(yōu)配置,The same rule of maximum utility pe

8、r hour can be applied to many different areas of life. It is not a merely a law of economics. It is a law of rational choice (理性選擇). 你是這樣考慮時(shí)間安排的嗎？,18,.,替代效應(yīng)和收入效應(yīng),5.3,.,無差異曲線方法,Over the last few decades, economists have developed an alternative approach (方法) to analysis of demandone that makes no men

9、tion of marginal utility. This alternative approach uses “indifference curves” (無差異曲線) to rigorously and consistently (嚴(yán)格和一致地) produce the major propositions about consumer behavior.,20,.,21,替代效應(yīng),The first factor explaining downward-sloping demand curve is the substitution effect (替代效應(yīng)). The substit

10、ution effect says that when the price of a good rises, consumers will tend to substitute other goods for the more expensive good in order to satisfy their desires more inexpensively.,.,22,收入效應(yīng),The second factor explaining downward-sloping demand curve is the income effect (收入效應(yīng)). The income effect d

11、enotes the impact of a price change on a goods quantity demanded that result from the effect of the price change on consumes real incomes.,.,23,名義收入和實(shí)際收入,We have to understand the difference between nominal income (名義收入) and real income (實(shí)際收入). Nominal income is the face value of what we have in our

12、 pocket or bank account. Real income signifies the actual amount of goods and services that your income can buy.,.,從個(gè)人到市場需求,5.4,.,25,個(gè)人需求與市場需求,市場需求等于：在各個(gè)價(jià)格下，每個(gè)消費(fèi)者的需求量分別相加。,.,關(guān)于市場需求的說明,由個(gè)人需求加總到市場需求，需要滿足消費(fèi)者之間不會(huì)相互影響的條件。 當(dāng)存在個(gè)人需求隨著購買物品的人數(shù)增加而增加，即人們所說的“攀比效應(yīng)”時(shí)，或者存在個(gè)人需求隨著購買物品的人數(shù)增加而減少，即人們所說的“虛榮效應(yīng)”時(shí)，消費(fèi)者互不影響的條件

13、將不滿足。,26,.,27,市場供給和生產(chǎn)者供給,市場供給一般不能像市場需求那樣，簡單地將不同價(jià)格水平下各個(gè)生產(chǎn)者的供給量相加而得到。 原因是，各個(gè)消費(fèi)者的需求之間是不能相互替代的，而各個(gè)生產(chǎn)者之間是相互競爭（替代）的。,.,替代品和互補(bǔ)品,Goods are substitutes (替代品) if an increase in the price of one increases the demand for the other. Goods are complements (互補(bǔ)品) if an increase in the price of one decreases the dem

14、and for the other. Goods are independent (無關(guān)的) if a price change for one has no effect on the demand for the other.,28,.,一些物品的需求價(jià)格彈性,29,.,價(jià)格彈性和替代品,The greater the number of substitutes for a good, the more elastic its demand will be. Beef has a lot of substitutes poultry (家禽), fish, and soy products

15、 (豆制品). In contrast, crack cocaine (強(qiáng)效可卡因) has little or no substitutes. Thats why a drug addicts (毒品上癮者) demand is much more inelastic than a beef eaters.,30,.,31,產(chǎn)品定義,In this regard, the elasticity of demand also depends on how narrowly the product is defined. For example, which do you think has a

16、 more elastic demand Chevron gas or gas? 產(chǎn)品定義不是一件容易的事情，它涉及“量變引起質(zhì)變”的分界問題，即“谷堆悖論”問題。,.,32,例子,The demand for Chevron gas is much more elastic than the demand for gas because many brands such as Shell and Texaco can be substituted for Chevron, but there is no good substitute for gas. 仍然是“同類物品越多，價(jià)格彈性越大”的

17、準(zhǔn)則。因此，“大類”劃分比“小類”劃分的同類更少。,.,33,收入彈性,The income elasticity denotes the percentage change in quantity demanded divided by the percentage change in income, holding other things, such as price, constant.,.,34,一些物品的收入彈性,.,35,按收入彈性的物品分類,Normal goods (正常品) : Eis are positive. Inferior goods (劣等品) : Eis are

18、 negative. Necessities (必需品) : Eis are positive but small. Luxuries (奢侈品) : Eis are high.,.,36,毒品經(jīng)濟(jì)學(xué),An addictive substance (上癮品) is one for which the desire to consume depends significantly on past consumption. By contrast, for conventional goods, demands today are not likely to depend so directly

19、on consumption patterns (消費(fèi)模式) yesterday.,.,37,(legal drugs),(illegal drugs),D,D,S,S,S,S,Quantity of addictive substance,Price of substance,Many of the negative consequences (負(fù)效應(yīng)) of illegal drugs result from the prohibition of addictive substances rather than from their consumption.,重度成癮者的需求,.,38,偶

20、爾染毒者的需求,(legal drugs),(illegal drugs),D,D,S,S,S,S,Quantity of addictive substance,Price of substance,Raising the prices of harmful addictive substances can reduce the number of casual users who will be attracted into the market.,.,塔利班禁止種鴉片,據(jù)聯(lián)合國毒品控制和犯罪預(yù)防辦公室統(tǒng)計(jì)，塔利班當(dāng)政期間，阿富汗的鴉片產(chǎn)量下降了94%。因?yàn)榘⒏缓沟镍f片產(chǎn)量占世界產(chǎn)量的約7

21、5%，產(chǎn)量下降直接反映為毒品市場生鴉片價(jià)格的變動(dòng)：2000年每公斤生鴉片價(jià)值為30美元，2001年飛漲到300美元，到9月初，隨著鴉片存量下降，一公斤生鴉片已經(jīng)賣到700美元。 摘自“廣州日報(bào)”2001年11月26日A20版,39,.,40,水與鉆石悖論,Adam Smith posed the paradox (悖論，似非而是的論點(diǎn)) of value: Nothing is useful than water; but it will scarce purchase anything. A diamond, on the contrary, has scarce any value in

22、use; but a very great quantity of other goods may frequently be in exchange for it.,.,41,價(jià)值悖論的解釋,The answer: The total utility from water consumption does not determine its price or demand. Rather, waters price is determined by its marginal utility, by the usefulness of the last glass of water. 鉆石屬于

23、炫耀品，不屬于正常商品。,.,42,消費(fèi)者剩余,The gap between the total utility of a good and its total market value is called consumer surplus (消費(fèi)者剩余). Because of diminishing marginal utility, consumers satisfaction exceeds what is paid.,.,個(gè)人的消費(fèi)者剩余,43,消費(fèi)者實(shí)際支付,價(jià)格,均衡 價(jià)格,數(shù)量,0,需求曲線,消費(fèi)者剩余,.,市場的消費(fèi)者剩余,Total purchases,Consumer

24、surplus,Quantity of water,Price and marginal utility of water,Price of water,44,市場以物品的邊際效用定價(jià)，稱之為邊際定價(jià)原則。,.,附錄1,消費(fèi)者均衡的幾何分析 （可以選讀附錄2的內(nèi)容）,.,46,無差異曲線,Suppose a consumer buys different combinations of two commodities, say, food and clothing, at a given set of price. If you were asked to choose between com

25、bination A and combination B, you might (1) prefer A to B, (2) prefer B to A, (3) be indifferent between A and B.,.,47,背景知識,無差異曲線方法是一種不同于基數(shù)效用論的方法，它是以序數(shù)效用論（ordinal utility theory）為基礎(chǔ)的。 它的特點(diǎn)在于，你可以不知道商品對于你的效用有多大，只要能夠在兩個(gè)商品組合之間進(jìn)行比較就可以了。,.,48,一個(gè)消費(fèi)者的無差異曲線,A,B,C,D,Food,Clothing,.,49,1,C,1,0.5,替代法則,The scarc

26、er a good, the greater its relative substitution value; its marginal utility rises relative to the marginal utility of the good that has become plentiful.,3,1,1,A,B,D,Food,Clothing,.,邊際替代率,50,C,F,.,無差異曲線圖,51,Food,Clothing,A Family of Indifference Curves (無差異曲線簇) : Curve U4 stands for a higher level

27、of satisfaction than U3; U3 for a higher level of satisfaction than U2; and so forth.,U4,U3,U2,U1,.,52,預(yù)算線和預(yù)算約束,Food,Clothing,6,4,4,2,0,2,6,Consumers budget line (預(yù)算線): PCQC+PFQF=$6,.,53,Food,Clothing,6,4,4,2,0,2,6,C,F,.,54,切線位置的均衡,Food,Clothing,U4,U3,U2,U1,B,等邊際原理：,.,55,收入變化,Food,Clothing,B,B”,.,單純

28、價(jià)格變化,56,B,B”,A rise in the price of food makes budget line pivot (繞轉(zhuǎn)) on N. The new tangency equilibrium is at B”, with less food but more or less clothing.,N,.,57,需求曲線的推導(dǎo),6,4,2,0,4,2,6,PF,QF,N,.,思考問題,“Over the last few decades, economists have developed an alternative approach to analysis of demand

29、one that makes no mention of marginal utility.” 無差異曲線方法能否避開“邊際效用遞減定律”？,58,.,小結(jié),效用和邊際效用 等邊際原理 替代效應(yīng)和收入效應(yīng) 替代品、互補(bǔ)品和獨(dú)立物品 收入彈性 消費(fèi)者剩余,59,.,謝謝！,60,.,附錄2,參考內(nèi)容,61,.,62,基數(shù)效用和序數(shù)效用,以具體的數(shù)值表示商品和勞務(wù)的效用的理論也稱為基數(shù)效用理論（cardinal utility theory），這一理論有其不合理性。 經(jīng)濟(jì)學(xué)家也可以用序數(shù)效用理論來說明消費(fèi)者的選擇行為。,.,63,消費(fèi)者的偏好,消費(fèi)者是同時(shí)消費(fèi)多種商品的，我們用“市場籃子”來表示多

30、種商品的集束。 消費(fèi)者在實(shí)際中是比較不同的市場籃子的效用大小。,.,一些基本假定,假定偏好是完全的，即消費(fèi)者可以比較或排列所有的市場籃子。如：在A和B中更偏好A，或更偏好B，或兩者無差異。 假定偏好是可傳遞的，指如果消費(fèi)者在A和B中更偏好A，在B和C中更偏好B，那么消費(fèi)者在A和C中更偏好A。 假定所有的商品都是“好的”，指在不計(jì)成本的情況下，消費(fèi)者總是偏好任何一種商品的多，而不是少。,64,.,無差異曲線,一條無差異曲線，又稱等效用曲線，代表了能帶給一個(gè)人相同程度滿足的市場籃子的所有組合。 市場籃子A、B、D具有相同的滿足程度。,65,衣服,O,40,30,20,10,10,20,30,40,

31、食物,50,50,B,A,D,.,如果商品是“好的”,市場籃子B好于市場籃子A，因?yàn)槭袌龌@子B的商品1和商品2的數(shù)量均大于市場籃子A。,66,商品2,商品1,A,B,.,對不同市場籃子的偏好,消費(fèi)者更偏好E而不是A。 消費(fèi)者更偏好A而不是G或H。,67,衣服,O,40,30,20,10,10,20,30,40,食物,50,50,B,A,E,D,H,G,.,無差異曲線不能相交,假如U1與U2相交，對U1來說，市場籃子A與D等效用，對U2來說，A與B等效用。因此，市場籃子B與 D等效用。但B優(yōu)于D，矛盾。,68,U1,U2,A,B,D,.,邊際替代率,從A到B，用1單位食物替代3單位衣服； 從B到

32、C，需要用2單位食物替代2單位衣服； 從C到D，需要用3單位食物替代2單位衣服。,69,衣服,食物,A,B,C,D,無差異曲線,.,無差異曲線的形狀,假定無差異曲線是凸的，即向內(nèi)彎曲的。 無差異曲線是凸的假定，意味著一種物品的數(shù)量越來越少時(shí)要求增加越來越多的其他物品。,70,.,完全替代品,如果物品之間可以完全替代，那么無差異曲線是直線。,71,5角幣,1元幣,6,4,2,1,2,3,.,完全不可替代品,如果物品之間可以完全不可替代，那么無差異曲線是成直角的線。 例如，一雙鞋與一雙鞋加一只左腳鞋的效用一樣。,72,左腳鞋,右腳鞋,3,2,1,1,2,3,.,無差異曲線簇,如果物品可以細(xì)分，那么

33、無差異曲線有無數(shù)根，構(gòu)成一個(gè)無差異曲線簇（a family of indifference curves）。 越是在外面的無差異曲線，代表的偏好越大。,73,U4,U3,U2,U1,.,給定預(yù)算約束的情形,如果食物的價(jià)格為每單位 1 元，衣服的價(jià)格為每單位 2 元。給定總預(yù)算 80 元。,74,.,75,用圖形描述預(yù)算約束,O,40,30,20,10,20,40,60,80,食物,衣服,.,76,預(yù)算約束和預(yù)算線,假定一個(gè)人的市場籃子由食物和衣服構(gòu)成，食物的價(jià)格為PF，數(shù)量為F，衣服的價(jià)格為PC，數(shù)量為C。 如果個(gè)人的預(yù)算（收入）是有限的，比方說為I，那么它能夠買的食物和衣服的組合全都在一條預(yù)算線上： PFFPCCI,.,預(yù)算線圖示,設(shè)食物的價(jià)格為PF，數(shù)量為F，衣服的價(jià)格為PC，數(shù)量為C。個(gè)人的預(yù)算（收入）為I。 PFFPCCI,77,衣服,食物,.,收入變化,給定食物和衣服的價(jià)格，當(dāng)收入增加時(shí)： 收入3 收入2 收入1,78,衣服,食物,收入2,收入1,收入3,.,消費(fèi)者的最優(yōu)選擇,最優(yōu)市場籃子由無差異曲線與預(yù)算線的切點(diǎn)確定。,79,衣服,食物,無差異曲線,最優(yōu)市場籃子,預(yù)算線,.,非最優(yōu)選擇,如果無差異曲線與預(yù)算線相交，選擇不是最優(yōu)。因?yàn)锽優(yōu)于D，卻選擇了A。,80,衣服,食物,無差異曲線,預(yù)算線,A,B,D,.,最優(yōu)選擇的特點(diǎn),從無差