消费者选择理论.ppt

Chapter 4 THE THEORY OF CONSUMER CHOICEPeople face trade-offs.The theory of consumer choice examines how consumers facing these trade-offs make decisions and how they respond to changes in their environment.如何做出选择，如何对环境的变化做出反应The Budget Constraint:what the consumer can affordSuppose the consumer has an income of$1,000 per month and he spends his entire income on pizza and Pepsi.假定收入1000美元，花费全部收入The price of a pizza is$10,and the price of a pint of Pepsi is$2.If the consumer spends all his income on pizza,how much pizzas he can eat during the month?全部购买比萨饼，能吃多少？If the consumer spends all his income on Pepsi,how much Pepsi he can drink during the month?全部购买百事可乐，能喝多少？ConsumptionBundle商品组合Quantityof Pizza比萨饼Quantityof Pepsi百事可乐Total spending总支出A05001000B204001000C403001000D602001000E10001000Budget constraint05003002040D20060100ABCEQuantityof PepsiQuantityof Pizza400lBudget constraint means the limit on the consumption bundles that a consumer can afford.l 预算约束线指对消预算约束线指对消费者可以支付得起的费者可以支付得起的消费组合的限制。消费组合的限制。Budget constraintn The slope of the budget constraint equals Quantityof Pizza0D500300200204060100ABCEQuantityof Pepsi400The slope of the budget constraintn the opportunity cost of one good measured by the other good.机会成本n the rate at which the consumer can trade one good for the other.交换比率n the relative price of the two goodsthe price of one good compared to the price of the other.两种商品的相对价格The equation of budget constraint0Quantityof X2 Quantityof X1 I=P1X1+P2X2Consumers income:I Two kinds of goods:X1,X2 Shifts in the budget constraintIf the income increases form$1000 to$1100 n an increase in income leads to a parallel shift in the budget constraint 平行移动Quantityof Pizza0D500300200204060100ABCEQuantityof Pepsi400If the price of Pepsi rises from$2 to$4 per pint.Quantityof Pizza0D500300200204060100ABCEQuantityof Pepsi400n a rise in the price of any good shifts the budget constraint inward.向里转动250Shifts in the budget constraintPreferences:what the consumer wantsMarket bundle(or basket)refers to a list with specific quantities of one or more goods.商品束指一种或几种商品的特定组合Preference means desire or liking for one thing rather than another.偏好意味着对一件东西比另一件更喜欢。Some basic assumptions about preferencesPreference are assumed to be complete.完备性For any two bundle A and B,a consumer will prefer A to B(AB),will prefer B to A(BA),or will be indifferent between the two(A=B).Preference are transitive.传递性If AB，and BC Then ACMore is better than less.Goods are assumed to be good,非饱和性if A(X1，Y1)，B(X1，Y2)，and Y1Y2 Then ABRepresenting preferences with indifference curvesQuantityof Pizza0ABCQuantityof Pepsil Indifference curve is a curve that shows consumption bundles that give the consumer the same level of satisfaction 无差异曲线一条表示给消费者相同满意程度的消费 组合的曲线The slope at any point on an indifference curve equals the Marginal rate of substitution,which is the rate at which a consumer is willing to trade one good for another.Quantityof X10BCQuantityof X2 amount of X2 willing to give upadditional unit of X1=-无差异曲线上任意一点的斜率表示边际无差异曲线上任意一点的斜率表示边际替代率，即指消费者愿意以一种物品交替代率，即指消费者愿意以一种物品交换另一种物品的比率。换另一种物品的比率。Marginal rate of substitutionFour properties of indifference curves Property 1:Higher indifference curves are preferred to lower ones.对较高无差异曲线的偏好大于较低的对较高无差异曲线的偏好大于较低的Quantityof Pizza0Quantityof PepsiABCDy1x1x2Consumers usually prefer more of something to less of it.I1I2Property 2:Indifference curves are downward sloping.右下方倾斜右下方倾斜Four properties of indifference curves Quantityof Pizza0Quantityof PepsiACy1x1x2y2Property 3:Indifference curves do not cross.不相交不相交Four properties of indifference curves I1I2BACQuantityof PepsiQuantityof Pizza0y1y2x1x2I1:A and B equally happyI2:B and C equally happy A and C would make the consumer equally happy,But A has more of both goods compared to C.Property 4:Indifference curves are bowed inward.凸向原点凸向原点Four properties of indifference curves 0DCBQuantityof PepsiQuantityof PizzaFrom D to CMRS=412348422.5From B to AMRS=0.5A People are more willing to trade away goods that they have in abundance and less willing to trade away goods of which they have little.愿意用多的去交换少的，不愿意用少的交换多的商品 The MRS diminishes along the curve.边际替代率递减Two extreme examples of indifference curves Perfect Substitutes:two goods with straight line indifference curves完全替代品，无差异曲线是直线the marginal rate of substitution is constant 边际替代率是常数I1 I2 I3milk1 2 33210coffeePerfect Complements:two goods with right angle indifference curves.完全互补品，直角形无差异曲线I1I2spectacle glass 眼镜片spectacle frame 眼镜架01 2 3 421Optimization:what the consumer choosesConsumers want to get the combination of goods on the highest possible indifference curve.最高可能无差异曲线上However,the consumer must also end up on or below his budget constraint.必须达到或低于预算约束线The highest indifference curve that the consumer can reach is the one that just barely touches his budget constraint.The point at which this indifference curve and the budget constraint touch is called the optimum.可以达到的最高无差异曲线与预算约束线相切，切点为最优点。The Consumers Optimumthe consumers valuation equals the markets valuation.消费者评价等于市消费者评价等于市场评价场评价Ethe MRS equals the relative price.Quantityof PizzaQuantityof Pepsi0Budget constraintI1I3OptimumABI2 假定假定MRSMRS1212=1/21/1=P=1/21/1=P1 1/P/P2 2=一元钱买苹果会比买梨多出半个苹果的满意度，一元钱买苹果会比买梨多出半个苹果的满意度，消费者会减少梨的购买而增加苹果的购买。消费者会减少梨的购买而增加苹果的购买。随苹果的不断增加，梨不断的减少，随苹果的不断增加，梨不断的减少，一个苹果的满意度逐渐降低，一个梨的满意度越来越高。一个苹果的满意度逐渐降低，一个梨的满意度越来越高。MRS MRS1212（=苹果苹果/梨）梨）逐渐变大，直至等于价格比，逐渐变大，直至等于价格比，达到最优状态。达到最优状态。假定假定MRSMRS1212=2/1=2/11/1=P1/1=P1 1/P/P2 2=一元钱买梨会比买苹果多出半个梨的满意度，一元钱买梨会比买苹果多出半个梨的满意度，消费者会减少苹果的购买而增加梨的购买。消费者会减少苹果的购买而增加梨的购买。随梨不断增加，苹果不断减少，随梨不断增加，苹果不断减少，一个梨的满意度逐渐降一个梨的满意度逐渐降低，一个苹果的满意度越来越高。低，一个苹果的满意度越来越高。MRSMRS1212逐渐变小，直至等于价格比，达到最优状态。逐渐变小，直至等于价格比，达到最优状态。某消费者收入为某消费者收入为30003000美元，一杯红酒美元，一杯红酒3 3美元，一磅美元，一磅奶酪奶酪6 6美元，画出该消费者的预算约束线，这条预美元，画出该消费者的预算约束线，这条预算约束线的斜率是多少？算约束线的斜率是多少？0奶酪奶酪 红酒红酒 5001000-P1/P2=-3/6=-0.5画出消费者对红酒和奶酪的无差异曲线。描述无差画出消费者对红酒和奶酪的无差异曲线。描述无差异曲线的四个特征。异曲线的四个特征。0I1奶酪奶酪红酒红酒选出红酒和奶酪无差异曲线上的一点，说明边际替选出红酒和奶酪无差异曲线上的一点，说明边际替代率，边际替代率告诉我们什么？代率，边际替代率告诉我们什么？I1奶酪奶酪红酒红酒0BC利用预算约束线和无差异曲线，说明最优消费选利用预算约束线和无差异曲线，说明最优消费选择。最优选择时，边际替代率是多少？择。最优选择时，边际替代率是多少？E0最优点最优点I1奶酪奶酪红酒红酒5001000How Changes in Income Affect the Consumers ChoicesAn increase in income shifts the budget constraint outward.收入增长使预算线向外移动The consumer is able to choose a better combination of goods on a higher indifference curve.消费者能够在更高的无差异曲线上选择更好的组合How Changes in Income Affect the Consumers Choices Normal versus Inferior GoodsIf a consumer buys more of a good when his or her income rises,the good is called a normal good.随收入增长，消费的数量增长-正常品If a consumer buys less of a good when his or her income rises,the good is called an inferior good。收入增长，消费的数量减少-劣等品消费红酒和奶酪的消费者收入增加到消费红酒和奶酪的消费者收入增加到40004000美元，说美元，说明如果红酒和奶酪都是正常品，收入增长对它们产明如果红酒和奶酪都是正常品，收入增长对它们产生什么影响生什么影响?A0最优点最优点I1奶酪奶酪红酒红酒I2新的最优点新的最优点C消费数量都增加消费数量都增加5001000消费红酒和奶酪的消费者收入增加到消费红酒和奶酪的消费者收入增加到40004000美元，如美元，如果奶酪是果奶酪是低档物品低档物品，收入增长又会对奶酪的消费量，收入增长又会对奶酪的消费量产生什么影响。产生什么影响。A0最优点最优点I1奶酪奶酪红酒红酒I2新的最优点新的最优点C低档物品数量减少低档物品数量减少5001000一磅一磅6 6美元上升到一磅美元上升到一磅1010美元美元价格不变，一杯价格不变，一杯3 3美元美元你的收入仍然是你的收入仍然是30003000美元，奶酪是正常物品，美元，奶酪是正常物品，你会如何调整对它的购买？你会如何调整对它的购买？How Changes in Prices Affect Consumers ChoicesA rise in the price of any good rotates the budget constraint outward and changes the slope of the budget constraint.商品价格上升，使预算线向外旋转，改变了预算线的斜率。C0新最优点新最优点I1奶酪奶酪红酒红酒I2最优点最优点A正常物品价格正常物品价格上升后，需求上升后，需求量减少量减少5001000300400150500价格变动产生两种影响价格变动产生两种影响:奶酪价格上升，红酒相对便宜，消费者会在维持奶酪价格上升，红酒相对便宜，消费者会在维持满意程度不变的条件下，用一定的红酒替代一定满意程度不变的条件下，用一定的红酒替代一定的奶酪，产生的奶酪，产生替代效应替代效应 奶酪价格上升，消费者收入相对减少，对于正常奶酪价格上升，消费者收入相对减少，对于正常品，奶酪的消费数量会减少，产生品，奶酪的消费数量会减少，产生收入效应收入效应 所以，价格上升后，奶酪需求数量减少。所以，价格上升后，奶酪需求数量减少。C0新最优点新最优点I1奶酪奶酪红酒红酒I2最优点最优点AyCyA总效应总效应:y yC Cy yA A 00补偿预算线，平补偿预算线，平行于新预算线，行于新预算线，与原无差异曲线与原无差异曲线相切相切ByB替代效应替代效应:y yB B y yA A 00收入效应收入效应:y yC C y yB B 0 0总效应总效应-替代效应替代效应=正常品：替代效应与价格反向，收入正常品：替代效应与价格反向，收入效应与价格反向，价格升，量减少。效应与价格反向，价格升，量减少。The Substitution Effectthe change in consumption that results when a price change moves the consumer along a given indifference curve to a point with a new marginal rate of substitution.当一个价格变动使消费者沿着既定的无差异曲线，移动到有新的边际替代率的一点时所引起的消费变动。Income and Substitution EffectsIncome and Substitution EffectsThe Income Effectthe change in consumption that results when a price change moves the consumer to a higher or lower indifference curve 一种价格变动使消费者移动到更高或更低无差异曲线时所引起的消费的变动。奶酪的价格由一磅奶酪的价格由一磅6 6美元上升到一磅美元上升到一磅1010美元，红酒美元，红酒的价格不变，对一个收入是的价格不变，对一个收入是30003000美元的消费者，如美元的消费者，如果奶酪是低档物品，他奶酪的消费会怎么变？果奶酪是低档物品，他奶酪的消费会怎么变？A0新最优点新最优点I1奶酪奶酪红酒红酒I2最优点最优点C低档物品价格上低档物品价格上升后，数量减少升后，数量减少A0新最优点新最优点I1奶酪奶酪红酒红酒I2最优点最优点C总效应总效应:y yC Cy yA A 00替代效应替代效应:y yB B y yA A 00 0总效应总效应-替代效应替代效应=低档品：替代效应与价格反向，收入低档品：替代效应与价格反向，收入效应与价格同向，价格升，量减少。效应与价格同向，价格升，量减少。yCyAyB补偿预算线，平补偿预算线，平行于新预算线，行于新预算线，与原无差异曲线与原无差异曲线相切相切B奶酪价格上升有可能使消费者购买更多的奶酪吗？奶酪价格上升有可能使消费者购买更多的奶酪吗？解释原因。解释原因。价格上升，替代效应会使奶酪数量下降，价格上升，替代效应会使奶酪数量下降，如果奶酪是低档品，则收入效应使奶酪数量上升，如果奶酪是低档品，则收入效应使奶酪数量上升，如果收入效应绝对值大于替代效应绝对值，则奶酪如果收入效应绝对值大于替代效应绝对值，则奶酪消费数量会增加，消费数量会增加，即价格上升，需求量增加，即价格上升，需求量增加，需求曲线呈现右上方倾斜的特点，需求曲线呈现右上方倾斜的特点，此时奶酪往往被称为吉芬商品，一类特殊的低档物此时奶酪往往被称为吉芬商品，一类特殊的低档物品。品。Giffen Good英国人吉芬于英国人吉芬于1919世纪发现，世纪发现，18451845年爱尔兰发生灾年爱尔兰发生灾荒，土豆价格上升，但是土豆的需求量却反而增荒，土豆价格上升，但是土豆的需求量却反而增加了。加了。Giffen goods are goods for which an increase in the price raises the quantity demanded.吉芬商品是指当价格上升，需求量增加的商品。Giffen goods is a kind of inferior good.The income effect dominates the substitution effect.是一种劣质商品，收入效应超过替代效应。A Giffen Good-the price increase Quantityof MeatQuantity ofPotatoes0I2I1DABOptimum with lowprice of potatoesOptimum with highprice of potatoesCA1.An increase in the price ofpotatoes rotates the budgetconstraint inward.ByAyByC总效应总效应:yC yA0收入效应收入效应:yC yB0替代效应替代效应:yB yA 0 TU上升上升MU=0 TU最大最大MU0 TU下降下降l边际效用与总效用边际效用与总效用Utility:An Alternative Way to DescribePreferences and Optimizationn消费者均衡消费者均衡Consumer Equilibrium 在消费者收入和商品价格既定的前提下，在消费者收入和商品价格既定的前提下，所购买的商品组合使消费者能获得最大效用的所购买的商品组合使消费者能获得最大效用的状态。状态。n 效用最大化原则（消费者均衡条件）效用最大化原则（消费者均衡条件）消费者购买的各种商品的边际效用与商品消费者购买的各种商品的边际效用与商品 价格成比例。价格成比例。Utility:An Alternative Way to DescribePreferences and Optimization前提：偏好（嗜好）既定前提：偏好（嗜好）既定 货币的边际效用假定不变货币的边际效用假定不变MU1P1=MU2P2=P1X1+P2X2=I消费者效用最大化的均衡条件：消费者效用最大化的均衡条件：商品价格既定，收入既定，消费者应使自己花费在商品价格既定，收入既定，消费者应使自己花费在各种商品购买上的最后一元钱的边际效用相等。各种商品购买上的最后一元钱的边际效用相等。Utility:An Alternative Way to DescribePreferences and Optimization某同学即将参加研究生入学考试，现只有6天时间复习，每门课的复习时间与对应的预期成绩如下表：天数0123456数学30446575838890政治40526270778388英语70808890919293为使预期成绩最高，应如何安排复习时间？天数0123456数学142110852政治12108765英语1082111 为什么像水那样对生命如此不可缺少的东为什么像水那样对生命如此不可缺少的东西只有很低的价格，而对于生命并非必不可少西只有很低的价格，而对于生命并非必不可少的钻石却极其昂贵？的钻石却极其昂贵？亚当亚当斯密的斯密的“价值悖论价值悖论”商品价格取决于商品的边际效用，一商品价格取决于商品的边际效用，一单位水的边际效用远远小于一单位钻石的单位水的边际效用远远小于一单位钻石的边际效用。边际效用。Five consumers have the following marginalutility of apples and pears:Marginal Utility Marginal Utility of Apples of PearsJerry 12 6George 6 6Elaine 6 3Kramer 3 6Newman 12 3The price of an apple is$2,and the price of a pear is$1.Which,if any,如果有的话，of these consumers are optimizing over their choice of fruit?For those who are not,how should they change their spending?这些消费者最优的水果选择是哪一个？对那些没有最优选择的人，如何改变支出？