厦门大学微观经济学 (3).ppt

微观经济学 (平狄克，鲁宾费尔德，第四版) LECTURE 3 消费者理论 1 一、消费者行为 2 基本概念 w市场篮子、无差异曲线、无差异曲线图 、边际替代率、效用、基数效用函数和 序数效用函数、预算约束、预算线、拐 点解、显示性偏好、边际效用、消费者 物价指数（CPI）、拉氏指数、派氏指数 、连锁权重物价指数 w消费者行为研究的三个步骤： n消费者偏好-预算约束-结合前面二者确定消 费者选择 3 消费者偏好 w基本假设： n偏好的完全性、可传递性，以及“多总比少好”。 w无差异曲线的特征： n向下倾斜 n其右上和左下分别表示偏好于和不偏好于 n每条无差异曲线绝不相交 n边际替代率（无差异曲线的斜率）递减（无差异曲 线是凸的）。 w完全替代品和完全互补品，图PP5，6。 w思考：BADS，无差异曲线将是怎么样的？ w序数排列就足以解释大多数消费者决策是如何做出的 。 4 Consumer Preferences Orange Juice (glasses) Apple Juice (glasses) 2341 1 2 3 4 0 Perfect Substitutes 5 Consumer Preferences Right Shoes Left Shoes 2341 1 2 3 4 0 Perfect Complements 6 预算约束 w预算线的斜率反映了两种商品的相对价格，是 两种商品价格比取负；截距表示使用已有收入 能够购买的最多单种商品。 w收入变化： n收入增加/减少使预算线向外/内平移。图PP8； w价格变化： n一种商品价格变化，预算线以另一种商品的截距点 为原点旋转。图：PP9； n两种商品价格发生同比变化，预算线斜率不变，向 外或向内平移。 7 Budget Constraints Food (units per week) Clothing (units per week) 8012016040 20 40 60 80 0 A increase in income shifts the budget line outward (I = $160) L2 (I = $80) L1 L3 (I = $40) A decrease in income shifts the budget line inward 8 Budget Constraints Food (units per week) Clothing (units per week) 8012016040 40 (PF = 1) L1 An increase in the price of food to $2.00 changes the slope of the budget line and rotates it inward. L3 (PF = 2) (PF = 1/2) L2 A decrease in the price of food to $.50 changes the slope of the budget line and rotates it outward. 9 消费者选择 w最大化消费者满足的市场篮子必须具备两个条 件： n应在预算线上， n应给予消费者最受偏好的商品和劳务组合。 w根据无差异曲线的斜率MRS=-C/F，预算线 斜率为-Pf/Pc，最大化条件是MRS=Pf/Pc w因此，当边际替代率等于两种商品价格比时， 消费者获得最大满足。图 PP11。 w拐点解： n发生在无差异曲线与横轴或纵轴相切时，此时 MRSPa/Pb。图 PP12。 10 U2 Consumer Choice Pc = $2 Pf = $1 I = $80 Budget Line A At market basket A the budget line and the indifference curve are tangent and no higher level of satisfaction can be attained. At A: MRS =Pf/Pc = .5 Food (units per week) Clothing (units per week) 408020 20 30 40 0 11 A Corner Solution Ice Cream (cup/month) Frozen Yogurt (cups monthly) B A U2U3U1 A corner solution exists at point B. 12 边际效用与消费者选择 w边际效用递减法则 w相等边际原则： n边际效用与无差异曲线： n又，在无差异曲线上：MRS=-C/F n因此 n又根据消费者最大化其满足感时有MRS=Pf/Pc n因此有效用最大化条件（相等边际原则）： 13 生活成本指数 w拉氏指数VS派氏指数： n两种指数都涉及基期和当前的价格水平对比 ； n拉氏指数立足于基期消费构成，派氏指数立 足于当前消费构成； n拉氏指数倾向于高估生活成本，派氏指数倾 向于低估生活成本。 14 二、个体需求和市场需求 15 个体需求 w需求曲线的两个特点： n沿曲线移动时可获得的效用发生变化； n曲线上的每点消费者都是通过实现两种商品的边际替 代率等于其价格比来实现效用最大化的。 w收入-消费曲线 n描画出与每种收入水平相联系的效用最大化商品组合 。 n收入增/减将使预算线右/左移，并使消费点沿收入-消 费曲线右/左移；同时使需求曲线右/左移。 n当收入-消费曲线有正的斜率时，需求随收入增加而增 加，需求的收入弹性为正，此种商品为正常商品； n当收入-消费曲线有负的斜率时，需求随收入增加而减 少，需求的收入弹性为负，此种商品为劣质商品。 16 An Inferior Good Hamburger (units per month) Steak (units per month) 15 30 U3 C Income-Consumption Curve but hamburger becomes an inferior good when the income consumption curve bends backward between B and C. 10520 5 10 A U1 B U2 Both hamburger and steak behave as a normal good, between A and B. 17 个体需求 w恩格尔曲线： n将商品的消费量与收入联系起来。 n正常商品的恩格尔曲线向上倾斜; n劣质商品的恩格尔曲线则向下倾斜。 18 Engel Curves Engel curves slope backward bending for inferior goods. Inferior Normal Food (units per month) 30 4812 10 Income ($ per month) 20 160 19 个体需求 w替代品VS互补品 n一种商品价格上涨/下跌导致另一种商品需求上升/ 下降，这两种商品是替代品； n一种商品价格上涨/下跌导致另一种商品需求下降/ 上升，这两种商品是互补品。 n价格消费曲线如向下倾斜，则两种商品被视为替代 品；该曲线向上倾斜，则两种商品被视为互补品； n值得注意的是，两种商品可能在一定条件下是前者 ，一旦条件改变（如收入变化）则变成后者。 20 Price-Consumption Curve 替代品VS互补品 Food (units per month) Clothing (units per month) 4 5 6 U2 U3 A B D U1 41220 A-B,替代品；B-D,互补品 21 个体需求 w替代效应与收入效应: n替代效应：在效用保持恒定的条件下因一种商品价 格变化而改变对该种商品的消费数量，一般是价格 下跌，消费数量增加。 n收入效应：在价格水平保持恒定的条件下因购买力 变化而改变对该种商品的消费数量，收入增加，对 某种商品的消费可能上升或下降。 n即便是劣质商品，收入效应也很少有可能大于替代 效应。 n吉芬商品：收入效应大于替代效应，导致对某种商 品的需求曲线向上倾斜。 22 Income and Substitution Effects: Normal Good Food (units per month)O Clothing (units per month) R F1S C1 A U1 The income effect, EF2, ( from D to B) keeps relative prices constant but increases purchasing power. Income Effect C2 F2T U2 B When the price of food falls, consumption increases by F1F2 as the consumer moves from A to B. E Total Effect Substitution Effect D The substitution effect,F1E, (from point A to D), changes the relative prices but keeps real income (satisfaction) constant. 23 Food (units per month) O R Clothing (units per month) F1SF2T A U1 E Substitution Effect D Total Effect Since food is an inferior good, the income effect is negative. However, the substitution effect is larger than the income effect. B Income Effect U2 Income and Substitution Effects: Inferior Good 24 市场需求 w市场需求曲线： n更多消费者进入市场将使市场需求曲线右移 ；影响众多消费者需求的因素也将影响市场 需求。 w需求的价格弹性： n需求的点弹性： n需求的弧弹性： w消费者剩余：图PP26 25 Demand Curve Consumer Surplus Actual Expenditure Consumer Surplus for the Market Demand Consumer Surplus Rock Concert Tickets Price ($ per ticket) 23456 13 01 14 15 16 17 18 19 20 Market Price 26 市场需求 w连带外部效应: n攀比效应: w原因：互相攀比，赶时髦。 w图 PP28-31. n虚荣效应: w原因：物以稀为贵。 w图 PP32-33. 27 Positive Network Externality: Bandwagon Effect Quantity (thousands per month) Price ($ per unit) D20 2040 When consumers believe more people have purchased the product, the demand curve shifts further to the the right . D40 60 D60 80 D80 100 D100 28 Demand Positive Network Externality: Bandwagon Effect Quantity (thousands per month) Price ($ per unit) D20 20406080100 D40D60D80D100The market demand curve is found by joining the points on the individual demand curves. It is relatively more elastic. 29 Demand Positive Network Externality: Bandwagon Effect Quantity (thousands per month) Price ($ per unit) D20 20406080 100 D40D60D80D100 Pure Price Effect 48 Suppose the price falls from $30 to $20. If there were no bandwagon effect, quantity demanded would only increase to 48,000 $20 $30 30 Demand Positive Network Externality: Bandwagon Effect Quantity (thousands per month) Price ($ per unit) D20 20406080 100 D40D60D80D100 Pure Price Effect $20 48 Bandwagon Effect But as more people buy the good, it becomes stylish to own it and the quantity demanded increases further. $30 31 Negative Network Externality: Snob Effect Quantity (thousands per month) Price ($ per unit) Demand 2 D2 $30,000 $15,000 14 Pure Price Effect Originally demand is D2, when consumers think 2000 people have bought a good. 468 D4 D6 D8 However, if consumers think 6,000 people have bought the good, demand shifts from D2 to D6 and its snob value has been reduced. 32 Negative Network Externality: Snob Effect Quantity (thousands per month) 2468 The demand is less elastic and as a snob good its value is greatly reduced if more people own it. Sales decrease as a result. Examples: Rolex watches and long lines at the ski lift. Price ($ per unit) D2 $30,000 $15,000 14 D4 D6 D8 Demand Pure Price Effect Snob Effect Net Effect 33 三、不确定条件下的选择 34 描绘风险 w正确计量风险必须了解： n行为可能导致的所有结果， n每种结果发生的概率。 w主观判断VS客观判断 w几个基本概念: n期望值: n方差 n标准差： 35 风险的偏好 w预期效用： n是各种结果根据发生概率进行加权的平均。 w风险规避VS风险中性VS风险偏好 n风险规避: w收入带来的边际效用递减的个体是风险规避型的 ； w对保险的运用体现了风险规避行为; w例子:PP37-42 n风险中性： 图PP43; n风险偏好: 图PP44. 36 一个例子 wA Scenario nA person can have a $20,000 job with 100% probability and receive a utility level of 16. nThe person could have a job with a .5 chance of earning $30,000 and a .5 chance of earning $10,000. Risk Averse 37 一个例子 wExpected Income = (0.5)($30,000) + (0.5)($10,000) = $20,000 Risk Averse 38 一个例子 wExpected income from both jobs is the same - risk averse may choose current job Risk Averse 39 一个例子 wThe expected utility from the new job is found: nE(u) = (1/2)u ($10,000) + (1/2)u ($30,000) nE(u) = (0.5)(10) + (0.5)(18) = 14 wE(u) of Job 1 is 16 which is greater than the E(u) of Job 2 which is 14. Risk Averse 40 一个例子 wThis individual would keep their present job since it provides them with more utility than the risky job. wThey are said to be risk averse. Risk Averse 41 Income ($1,000) Utility The consumer is risk averse because she would prefer a certain income of $20,000 to a gamble with a .5 probability of $10,000 and a .5 probability of $30,000. E 10 101520 13 14 16 18 0 1630 A B C D 一个例子 42 Income ($1,000) 1020 Utility 030 6 A E C 12 18 The consumer is risk neutral and is indifferent between certain events and uncertain events with the same expected income. Risk Neutral 43 Income ($1,000) Utility 0 3 102030 A E C 8 18 The consumer is risk loving because she would prefer the gamble to a certain income. Risk Loving 44 风险的偏好 w风险溢价： n结果可能的变动越大，风险就越大，风险溢 价也越大。 n例:PP46-51. 45 风险溢价举例 wA Scenario nThe person has a .5 probability of earning $30,000 and a .5 probability of earning $10,000 (expected income = $20,000). nThe expected utility of these two outcomes can be found: wE(u) = .5(18) + .5(10) = 14 wQuestion nHow much would the person pay to avoid risk? 46 Income ($1,000) Utility 0 1016 Here , the risk premium is $4,000 because a certain income of $16,000 gives the person the same expected utility as the uncertain income that has an expected value of $20,000. 10 18 3040 20 14 A C E G 20 F Risk Premium 风险溢价举例 47 风险溢价举例(续) wVariability in potential payoffs increase the risk premium. wExample: nA job has a .5 probability of paying $40,000 (utility of 20) and a .5 chance of paying 0 (utility of 0). 48 风险溢价举例(续) wExample: nThe expected income is still $20,000, but the expected utility falls to 10. nExpected utility = .5u($) + .5u($40,000) = 0 + .5(20) = 10