1、Chapter 3Consumer BehaviorConsumer Behavior消费者行为The Basic Framework of MicroeconomicsProducer 生产者生产者Consumer 消费者消费者Choice (production)生产选择Choice (purchase)购买选择购买选择Supply供给 Demand需求需求 Market市场市场Outline3.1 Consumer Preferences 消费者偏好3.2 Budget Constraints 预算约束3.3 Consumer Choice 消费者选择3.4 Revealed Prefe
2、rence 显示性偏好3.5 Marginal Utility and Consumer Choice3.6 Cost-of-Living Indexes消费者行为理论的基础【经济学】看社会问题 个人状况条件是否个人状况条件是否相同相同？ 虽然个人状况条件虽然个人状况条件不同不同，是否存在普，是否存在普遍的規律性？遍的規律性？ 掌握人性的規律掌握人性的規律现现象，有助象，有助进进一步依一步依据个据个別狀況別狀況并并結合結合环环境因素分析境因素分析！ 一般一般个个人狀況往往不同！人狀況往往不同！（从从微观微观开始开始） 法法则则（经济学帮经济学帮我我们们找！）找！） 更好的结果更好的结果！个体面
3、对个体面对一一般般事物的共事物的共同同观念观念正常人正常人还还是是怪人怪人？（柳下惠、（柳下惠、怪癖怪癖、丁丁客客族族）如何如何摆脱摆脱命命运的枷锁运的枷锁？边际效用递减法则边际效用递减法则无差异曲线无差异曲线（描绘个性描绘个性的利器）的利器）中华文化之中华文化之“中庸之道中庸之道” 边际替代率递减边际替代率递减其他条件改变其他条件改变flickr adwriterConsumer Behavior 消费者行为theory of consumer behavior Description of how consumers allocate incomes among different goo
4、ds and services to maximize their well-being.Consumer behavior is best understood in three distinct steps:1. Consumer preferences 消费者偏好消费者偏好2. Budget constraints 预算约束预算约束3. Consumer choices 消费者选择消费者选择3.1 Consumer PreferencesMarket BasketsMarket Baskets（市场篮子）（市场篮子）market basket (or bundle商品束商品束) 一种或多
5、一种或多种商品的一个组合。种商品的一个组合。TABLE 3.1 Alternative Market BasketsA2030B1050D4020E3040G1020H1040Market BasketUnits of FoodUnits of ClothingTo explain the theory of consumer behavior, we will ask whether consumers prefer one market basket to another.Some Basic Assumptions about Preferences 有关偏好的基本假设完备性 （ Com
6、pletenessCompleteness ）可传递性（ TransitivityTransitivity ）越多越好（ More is better than lessMore is better than less ）.or indifferenteither.or.Completeness 完备性Completeness 完备性消费者可以对所有可能的消费束进行比较和排序。对于任两个市场篮子A和B, 消费者或者偏好A，或者偏好B，或者觉得两者无差异。 注意这里的偏好是忽略成本的。Transitivity 传递性thenifandTransitivityTransitivity means
7、that if a consumer prefers basket A to basket B and basket B to basket C, then the consumer also prefers A to C. 可传递性通常被认为是消费者保持一致性（consistency）的必要条件.More is better than less (Greed)商品被假定为好的（good）.消费者偏好好的商品多一些，而不是少一些。 消费者是永不满足的，多总是好的，哪怕只多一点点。 Take any consumption bundle in X.x1x2This is the greed as
8、sumption.These bundles must be preferred to AAl .giving us a clear directionincreasingpreferenceX1、x2分别代表分别代表消费者可选择的消费者可选择的一个市场篮子中一个市场篮子中的两种商品的两种商品Based on the assumption of greed, basket A is clearly preferred to basket G, while E is clearly preferred to A.However, A cannot be compared with B, D, o
9、r H without additional information.要比较要比较A、B、H和和D点的点的偏好程度，我们需要无差偏好程度，我们需要无差异曲线。异曲线。通过通过A点的无差异曲线表明，点的无差异曲线表明，B点和点和D点与点与A点的偏好是点的偏好是无差异的，即这三个市场篮无差异的，即这三个市场篮子可以带给消费者相同的满子可以带给消费者相同的满意程度。意程度。 Indifference curves Indifference curves 无差异曲线无差异曲线无差异曲线代表了能带给消费者相同满足程度的所有市场篮无差异曲线代表了能带给消费者相同满足程度的所有市场篮子的组合。子的组合。刻画
10、偏好的一个工具。刻画偏好的一个工具。Our consumer prefers basket E, which lies above U1, to A, but prefers A to H or G, which lie below U1.Slopes of Indifference CurvesWhen more of a commodity is always preferred, the commodity is a good.If every commodity is a good then indifference curves are negatively sloped.If ev
11、ery commodity is a good then indifference curves are negatively sloped.Slopes of Indifference CurvesIf less of a commodity is always preferred then the commodity is a bad（厌恶（厌恶品）品）.One good and onebad a positively sloped indifference curve.One good and onebad a positively sloped indifference curve.I
12、ndifference Maps Indifference Maps 无差异曲线族无差异曲线族 Graph containing a set of indifference curves showing the market baskets among which a consumer is indifferent.Any market basket on indifference curve U3, such as basket A, is preferred to any basket on curve U2 (e.g., basket B), which in turn is prefe
13、rred to any basket on U1, such as D.If indifference curves U1 and U2 intersect, one of the assumptions of consumer theory is violated.Indifference Curves Cannot Intersect无差异曲线不能相交无差异曲线不能相交According to this diagram, the consumer should be indifferent among market baskets A, B, and D. Yet B should be
14、preferred to D because B has more of both goods.（极限）任意一点的（极限）任意一点的边际替代率等于无差边际替代率等于无差异曲线在该点的斜率异曲线在该点的斜率的绝对值。的绝对值。The Marginal Rate of Substitution The Marginal Rate of Substitution 边际替代率边际替代率边际替代率（边际替代率（MRSMRS）是消费者为了获得额外的一单位）是消费者为了获得额外的一单位商品商品x x1 1（横轴商品）而愿意放弃的商品（横轴商品）而愿意放弃的商品x x2 2的的最大数量最大数量。XYMRSXY
15、（1,16）（2,10）The Marginal Rate of Substitution The Marginal Rate of Substitution 边际替代率边际替代率In this figure, the MRS between clothing (C) and food (F) falls from 6 (between A and B) to 4 (between B and D) to 2 (between D and E) to 1 (between E and G).Maximum amount of a good that a consumer is willing
16、to give up in order to obtain one additional unit of another good.无差异曲线的凸性无差异曲线的凸性( Convexity) 即意味着边际替代率递减边际替代率递减（diminishing marginal rate of substitution ）. When the MRS diminishes along an indifference curve, the curve is convex. MRS=6MRS=4MRS=2MRS=1凸偏好的含义消费者偏好为凸的，两种商品的情况下，意味着无差异曲线凸向原点，即向内弯曲；此时无差
17、异曲线随x1增大越来越平坦，因为无差异曲线斜率为边际替代率（MRS），因此凸偏好意味着边际替代率（绝对值）递减；随着一种商品消费量的日益增加，为了获得额外一单位此商品而愿意放弃的其他商品的数量会越来越少；如果两个消费束x和y处于同一条无差异曲线，则连线上所有点位于更高的无差异曲线：“平均”好于“极端”，消费者更喜欢消费物品的多样性；凸偏好意味着最优的选择只有一个。0UAB家花魅力放弃野花当初见面，家花的魅力只要一些，就可以使我放弃所有的野花。现在如果家花用同样的魅力，我只愿意牺牲一些野花。家花魅力放弃野花家花没有野花香家花没有野花香边际替代率递减边际替代率递减Perfect Substitut
18、es and Perfect Complements完全替代品：无差异曲线为直线，边际替代率为常数完全互补品：无差异曲线为直角，MRS等于0或者无穷大(a) perfect substitutesPerfect Substitutes and Perfect ComplementsPerfect Substitutes and Perfect Complements(b) perfect complements黑猫白猫，逮住老鼠就是好猫黑猫白猫，逮住老鼠就是好猫一个萝卜一个坑一个萝卜一个坑标准无差异曲线的标准无差异曲线的中庸之道中庸之道 0U钱钱闲闲过与过与不及都不好不及都不好，人生人生追求一
19、追求一种种平衡平衡特殊偏好的特殊偏好的 无差异曲线实例:1.素食者（y:肉）2.給我玩具(x)其余(y)免谈！0U1U2U3U4U3.熊貓（x:竹子，y:其他）X（素食）y(肉)4.丁客族（y:小孩）中性物品中性物品 无差异曲线柳下惠：柳下惠：x “美色美色” 2.色盲的色盲的“红绿灯红绿灯(x)”！xy同理同理: : 1. 再多再多“苦苦(x)”我也不在乎！我也不在乎！flickr tanakawho含bad的无差异曲线 随着随着bad(x)消费量渐增，对消费量渐增，对bad(x)的反感与日俱增，此时每增加一的反感与日俱增，此时每增加一单位单位bad(x)，必须以更多的，必须以更多的good
20、(y)即即y1y2来弥补，才能维来弥补，才能维持效用不变！持效用不变！X为为bad（如垃圾、（如垃圾、风险风险），），y为为good0UAxB y2 y1xyxbadbadbadbadxy再給我一袋垃圾再給我一袋垃圾我就要抓狂我就要抓狂啦啦反正已经那么脏反正已经那么脏了，算了，别那了，算了，别那么在意么在意哀莫大于心死哀莫大于心死无差异曲线的形状无差异曲线的形状说明了消费者对于两种商品相互替代的愿意程度不同形状的无差异曲线表明了替代愿意程度的不同。无差异曲线越陡峭，说明Preferences for Automobile Attributes福特野马的拥有者福特野马的拥有者福特探索者的拥有者福
21、特探索者的拥有者无差异曲线的形状无差异曲线的形状说明了消费者对于两种商品相互替代的愿意程度不同形状的无差异曲线表明了替代愿意程度的不同。无差异曲线越陡峭，说明这个消费者同另一个消费者相比更偏好于商品1（横轴），MRS更高注意不同形状的无差异曲线的比较是不同消费者之间的比较幸福是什么？幸福是什么？钱？别墅？私人飞机？口渴时一瓶矿泉水？瞌睡时温暖的床？和男（女）朋友一起吃路边摊？钻戒？保罗萨缪尔森 1915-2009欲望效用幸福 萨缪尔森提出的幸福方程式：Utility 效用效用UtilityNumerical score representing the satisfaction that a
22、consumer gets from a given market basket.效用是消费者从一个市场篮子中得到的满足程度的数值表示。消费者从商品消费中得到的满足程度。 （高鸿业版）Utility 效用效用说明：效用是消费者的主观评价；一种物品有效用不一定有价值或价格（如空气）； 效用本身不具有伦理学的意义，不论欲望的好坏善恶，如吸毒； 效用本身有正有负； 效用因人、因地、因时而不同Ordinal versus Cardinal Utility序数效用和基数效用序数效用和基数效用Ordinal utility function（序数效用）utility function that gener
23、ates a ranking of market baskets in order of most to least preferred.Cardinal utility function（基数效用）utility function describing by how much one market basket is preferred to another.Utility Functions 效用函数utility functionFormula that assigns a level of utility to individual market baskets.效用函数为赋予每一个市
24、场篮子一定效用水平的方程。A utility function represents preferences.U(x) U(x)x xlU-functions represent orderings lSo the utility scales dont matterlAnd you can transform the U-function in any (monotonic) way you want.Tricks with utility functionsSo take any utility function. log ( )U(x1, x2,., xn)this transforma
25、tion represents the same preferences. U(x1, x2,., xn)and so does this . exp( ).and this (f f is a monotonic function) f f( ) And, in general, this. And, in general, this. n( )A utility functionu0U(x1,x2)x2x1Take a slice at given utility level indifference curveA utility function can be represented b
26、y a set of indifference curves, each with a numerical indicator.u(F,C) = FCThis figure shows three indifference curves (with utility levels of 25, 50, and 100, respectively) associated with the utility function:Utility Functions 效用函数Utility Functions 效用函数效用函数There is no unique utility function repre
27、sentation of a preference relation.一个给定的偏好关系的效用函数不止一个。Suppose U(x1,x2) = x1x2 represents a preference relation.orDefine V = U2 or V = 4UV preserves the same order as U and so represents the same preferences.u(F,C) = FC=k效用函数与无差异曲线nThe general equation for an indifference curve is U(x1,x2) k, a const
28、ant.n一个效用函数可以用一个无差异曲线族来表示Clothing (C)Budget constraints 预算约束Market baskets associated with the budget line F + 2C = $80budget constraints Constraints that consumers face as a result of limited incomes.budget line All combinations of goods for which the total amount of money spent is equal to income.
29、TABLE 3.2 Market Baskets and the Budget LineA 040$80B2030$80D4020$80E6010$80G80 0$80Market BasketFood (F)Total SpendingLine AG (which passes through points B, D, and E) shows the budget associated with an income of $80, a price of food of PF = $1 per unit, and a price of clothing of PC = $2 per unit
30、.The slope of the budget line (measured between points B and D) is PF/PC = 10/20 = 1/2.The Budget LineThe Budget Linex1x2the budget constraint & the budget linethe budget constraintthe budget linep1 M x1x2p2 M How to draw a budget lineWhat determines its shape and position?p1p2Slope - the role of pr
31、icesPosition the incomen Fixed by amount of money income M Income changes A change in income (with prices unchanged) causes the budget line to shift parallel to the original line (L1).When the income of $80 (on L1) is increased to $160, the budget line shifts outward to L2.If the income falls to $40
32、, the line shifts inward to L3.The Effects of Changes in Income and PricesThe Effects of Changes in Income and PricesBudget constraints 预算约束预算约束Price changes A change in the price of one good (with income unchanged) causes the budget line to rotate about one intercept.When the price of food falls fr
33、om $1.00 to $0.50, the budget line rotates outward from L1 to L2.However, when the price increases from $1.00 to $2.00, the line rotates inward from L1 to L3.The Effects of Changes in Income and PricesThe Effects of Changes in Income and PricesBudget constraints 预算约束预算约束The maximizing market basket
34、must satisfy two conditions:1. It must be located on the budget line.2. It must give the consumer the most preferred combination of goods and services.Consumer Choice 消费者选择消费者选择The consumer aims to maximise utility.increasingpreference subject to the budget constraint x2x1Constraint setl A*Indiffere
35、nce mapConsumer Choice 消费者选择At A point, the budget line and indifference curve U2 are tangent.No higher level of satisfaction (e.g., market basket D) can be attained.At B, however, because the MRS (10/10) = 1 is greater than the price ratio (1/2), satisfaction is not maximized.At A, the point of max
36、imization, the MRS between the two goods equals the price ratio.MRS =goods price ratio= PF/PCmarginal benefit Benefit from the consumption of one additional unit of a good.marginal cost Cost of one additional unit of a good. Using these definitions, we can then say that satisfaction is maximized whe
37、n the marginal benefit is equal to the marginal cost. The marginal benefit is measured by the MRS. The marginal cost is measured by the slope of the budget line.Satisfaction is maximized (given the budget constraint) at the point where MRS = PF/PC.Consumer Choice of Automobile AttributesThe consumer
38、s in (a) are willing to trade off a considerable amount of interior space for some additional acceleration. Given a budget constraint, they will choose a car that emphasizes acceleration. The opposite is true for consumers in (b).Figure 3.14Corner Solutions 角点解the consumer maximizes satisfaction by
39、consuming only one of the two goods.the MRS (of ice cream for frozen yogurt) is greater than the ratio of the price of ice cream to the price of frozen yogurt.Situation in which the marginal rate of substitution for one good in a chosen market basket is not equal to the slope of the budget line.思考课后
40、复习题，第4题，第100页When given a college trust fund that must be spent on education, the student moves from A to B, a corner solution.If, however, the trust fund could be spent on other consumption as well as education, the student would be better off at C.显示性偏好显示性偏好理论(Revealed Preference Theory )是由P.Samue
41、lson提出来的，其基本精神是：消费者在一定价格条件下的购买行为暴露了或显示了他内在的偏好倾向。因此我们可以根据消费者的购买行为来推测消费者的偏好。这是一种不基于“偏好关系（效用函数）消费者选择”的逻辑思路，而是一个相反的过程，即“消费者选择偏好关系”。Revealed PreferenceA is revealed preferred to B.And A is preferred to all market baskets in the green-shaded area.the bundle x* is chosen when the bundle y is affordable. Th
42、en x* is directly revealed preferred to y (otherwise y would have been chosen) （x直接显示性偏好于y）.Revealed PreferenceD is not affordable when A is chosen.A is not affordable when D is chosen.So A and D cannot be compared directly.Revealed PreferenceA is revealed preferred to B.B is revealed preferred to D
43、.Then A is indirectly revealed preferred to D.A is preferred to all market baskets in the green-shaded area.Suppose x is revealed directly preferred to y, and y is revealed directly preferred to z. Then, by transitivity, x is indirectly revealed preferred to z. （x间接显示性偏好于z）Facing budget line l3 the
44、individual chooses E, which is revealed preferred to A.Likewise, facing line l4, the individual chooses G which is also revealed preferred to A.Whereas A is preferred to all market baskets in the green-shaded area, all market baskets in the pink-shaded area are preferred to A.Revealed PreferenceTake
45、 any consumption bundle, A.Take any consumption bundle, A.Construct two other bundles, one with Better than A, one with WorseThere is a set of points like W, and a set like BAx1x2 B Wbetter than A?worse than A?what about the boundary points between the two?then we get.The indifference curveThe Weak
46、Axiom of Revealed The Weak Axiom of Revealed Preference (WARP)Preference (WARP)弱显示性偏好弱显示性偏好If the bundle x is directly revealed preferred to the bundle y then it is never the case that y is directly r e v e a l e d p r e f e r r e d t o x ; i . e . x y not (y x).如果消费束x直接显示偏好于消费束y，那么消费束y不可能直接显示偏好于消费束
47、x显示偏好的弱公理Dp pDp pWARP rules out this preference pattern. Take the original equilibriumx2Ax1Mondays pricesMondays choiceBA is chosen when B is availableso A is directly revealed preferred to B.Now let prices and the budget change.x2Ax1Mondays pricesMondays choiceTuesdays pricescan still afford the or
48、iginal choiceBBB violates WARP B does notB is chosen when A is availableso Bis directly revealed preferred to A.Choose A and B are inconsistent with each other.WARP rules out this preference pattern.but not thisYou need the strong axiom ofrevealed preference to getany further on this one.The Strong
49、Axiom of Revealed Preference (SARP)如果消费束x直接或者间接显示偏好于y且x y, 那么消费束y不可能直接或者间接显示偏好于; 即 x y or x ynot ( y x or y x ).Dp pDp pIp pIp pmarginal utility (MU) Additional satisfaction obtained from consuming one additional unit of a good.边际效用度量了从消费额外一单位的商品中所获得的额外的满足。边际意味着“增量”.商品的边际效用 是总效用的改变量与 消费量的改变量之比Margin
50、al Utility and Consumer ChoiceiixUMUu0U(x1,x2)x2x1Now take a vertical section.l U（x1）ux1good 1 is essentialTake the relationship between utility and good 1.nKeep all but one good constant nMeasure change in utility with regard to this goodx1uU(x)u1 falls with x1 “law of diminishing marginal utility”
