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1、第四章 个人需求和市场需求,Chapter 4,Slide 1,本章讨论的主题,个人需求收入效应与替代效应市场需求消费者需求连带外部效应,Chapter 4,Slide 2,4.1 个人需求,价格变化运用前几章学习的图形，通过无差异曲线，我们可以说明食品价格变化对需求量产生的影响。,Chapter 4,Slide 3,价格变化的影响,Chapter 4,Slide 4,食物,衣服,价格变化的影响,Chapter 4,Slide 5,价格消费曲线,食物,衣服,4,5,6,U2,U3,A,B,D,U1,4,12,20,价格消费曲线将与食物的每一种价格相对应的效用最大化的商品组合连结起来。,需求曲线
2、,Chapter 4,Slide 6,食物数量,食物的价格,4.1 个人需求,个人需求曲线的两大特征1)当我们沿着需求曲线向下移动时，我们所能获得效用水平不断增加。2）当我们沿着需求曲线下移时，食物对衣服的MRS逐渐下降。当消费者购买更多食物的时候，食物的相对价值便下降了。,Chapter 4,Slide 7,个人需求曲线,价格变化的影响,Chapter 4,Slide 8,食物数量,食物价格,个人需求,收入变化利用前几章学习的图形，收入变化对消费的影响可以通过无差异曲线表现出来。,Chapter 4,Slide 9,收入变化的影响,Chapter 4,Slide 10,食物,衣服,在价格不变
3、的条件下，收入的提高会导致消费者改变其市场篮子。,假设:Pf=$1 Pc=$2 I=$10,$20,$30,收入变化的影响,Chapter 4,Slide 11,食物数量,食物的价格,在价格不变的情况下，收入的提高会导致消费者的需求曲线向右移动。,4.1 个人需求,收入变化收入消费曲线描述了在每一个收入水平下，使消费者效用实现最大化的衣服与食物的所有组合。收入的增加使得预算线向右移动，沿着收入消费曲线向上，消费量也增加了。同时，随着收入的增加，需求曲线也向右移动。,Chapter 4,Slide 12,4.1 个别需求,收入变化如果收入消费曲线的斜率为正，意味着:需求量随着收入的提高而增加。商
4、品需求的收入弹性为正值。这种商品就是正常商品（normal good）。,Chapter 4,Slide 13,正常商品与低档商品,4.1 个别需求,如果收入消费需求的斜率为负，这意味着：需求量随着收入的提高而减少。商品需求的收入弹性为负值。这种商品就是低档商品（inferior good）。,Chapter 4,Slide 14,一种劣等商品,Chapter 4,Slide 15,汉堡包,牛排,收入消费曲线,但是，在B和C之间，收入消费曲线向后弯曲，汉堡包就成了劣等商品。,4.1 个别需求,恩格尔曲线恩格尔曲线（Engel curves）将一种商品的消费量与收入联系起来。如果一种商品是正常商
5、品，恩格尔曲线是向上倾斜的。如果一种商品是劣等商品，恩格尔曲线就是向下倾斜的。,Chapter 4,Slide 16,恩格尔曲线,Chapter 4,Slide 17,食物,30,4,8,12,10,收入,20,16,0,恩格尔曲线,Chapter 4,Slide 18,食物,30,4,8,12,10,收入,20,16,0,例4.1 美国的消费支出,娱乐52089411851602201825654007自有住房854137021223314445056169736租用住房164221281978188418021514748保健护理1034164717321881201220542703食物
6、2461319839714706555662738137衣服867106813941778221523163668,支出项目 10,0001,000-20,000-30,000-40,000-50,000-70,000-以下19,00029,00039,00049,00069,000以上,收入组(1993年美元),4.1 个别需求,1)如果一种商品的价格上涨（下跌）导致另一种商品需求量的上升（下降），那么，这两种商品就是替代品。例如，电影票与录像带,Chapter 4,Slide 20,替代品和互补品,4.1 个别需求,2)如果一种商品的价格上涨（下跌）导致另一种商品需求量的下降（上升），那么
7、，这两种商品就是互补品。例如，汽油与机油,Chapter 4,Slide 21,4.1 个别需求,3)如果一种商品价格的变化对另一种商品的需求量没有影响，那么，这两种商品就是独立的。,Chapter 4,Slide 22,4.1 个别需求,要分清商品是替代品或互补品，可以观察价格消费曲线。如果价格消费曲线是向下倾斜的，那么，两种商品是替代品。如果价格消费曲线是向上倾斜的，那么，两种商品是互补品。,Chapter 4,Slide 23,4.2 收入效应和替代效应,一种商品价格的变化有两种效应:收入效应与替代效应收入效应（Income Effect）：一种商品的价格下降导致消费者的实际购买力提高。
8、替代效应（Substitution Effect）：消费者倾向于更多地购买那些相对变得便宜的商品，而减少购买那些变得相对较贵的商品。,Chapter 4,Slide 24,4.2 收入效应和替代效应,收入效应收入效应（income effect）是在一种价格保持不变的情况下购买力的增加造成的该商品消费方面的变化。正常品，当一个消费者的收入增加时，他对商品的需求量会增加。低档品，收入增加，需求量减少。,Chapter 4,Slide 25,4.2 收入效应和替代效应,替代效应替代效应是在效应水平保持不变的情况下，与一种商品的价格变化相联系的该商品消费量的变化。当一种商品价格下降，替代效应往往导致
9、该商品的需求量增加。,Chapter 4,Slide 26,收入效应与替代效应,Chapter 4,Slide 27,食物,O,衣服,E,总效应,替代效应,D,改变商品相对价格，但保持实际收入（满足程度）不变，替代效应F1E（从A点移动到D点）。,对于正常物品替代效应与价格成反方向变化，收入效应也与价格成反方向变化，在它们共同作用下，总效应必定与价格成反方向变动。正因为如此，正常物品的需求曲线向右下方倾斜。,Chapter 4,Slide 28,收入效应与替代效应：低档商品,Chapter 4,Slide 29,食物,O,R,衣服,F1,S,F2,T,A,U1,E,替代效应,D,对于低档物品，
10、替代效用与价格成反方向变动，收入效应与价格成同方向变动，在大多数场合，收入效应的作用小于替代效应的作用，所以总效用成反方向变动。需求曲线向右下方倾斜。,Chapter 4,Slide 30,收入效应与替代效应,一个特例吉芬商品英国人吉芬在19世纪提出。在理论上，收入效应可以大到使某种商品的需求曲线向上倾斜，这种商品称为吉芬商品。,Chapter 4,Slide 31,例4.2 汽油税的影响,假设需求的价格弹性=-0.5收入=9,000美元汽油价格=1美元,Chapter 4,Slide 32,例4.2 汽油税的影响,Chapter 4,Slide 33,Gasoline Consumption
11、(gallons/year),其他商品的支出,A,C,最初，消费者在C点消费，汽油1200，其他支出7800。,U2,1200,原预算线,B,D,U1,900,征收汽油税后的预算线。,E,征收0.5汽油税后，消费汽油900加仑。,J,F,H,913.5,征收汽油税又加上退还后的预算线,U3,退税450美元，面临新的预算线，消费者满足下降。,4.3 市场需求,市场需求曲线市场需求曲线描述了在商品的每一个价格水平下所对应的所有消费者的需求总量。,Chapter 4,Slide 34,从个别需求到市场需求,市场需求曲线的确定,161016322481325326101840471150246,Cha
12、pter 4,Slide 35,价格个人A个人B个人C市场($)(units)(units)(units)(units),通过加总获得市场需求曲线,Chapter 4,Slide 36,数量,1,2,3,4,价格,0,5,5,10,15,20,25,30,4.3 市场需求,应注意的两点：1)当更多的消费者进入市场时，市场需求曲线将会右移。2)影响许多消费者需求的因素也会影响市场需求。,Chapter 4,Slide 37,4.3 市场需求,需求弹性,Chapter 4,Slide 38,价格弹性和消费支出,需求如果价格上涨,如果价格下降,开支:开支:,Chapter 4,Slide 39,缺乏
13、弹性(Ep 1)减少增加,4.3 市场需求,需求的点弹性在价格变化较大时（如20%），弹性值的大小有赖于需求曲线上不同点的价格与数量。,Chapter 4,Slide 40,4.3 市场需求,需求的点弹性点弹性（Point elasticity）衡量需求曲线某一特定点的价格弹性。其公式为：,Chapter 4,Slide 41,4.3 市场需求,运用点弹性存在的问题我们或许需要计算需求曲线某一段的弹性而不仅仅只是某一点的弹性。采用不同的价格与数量作为初始值将影响需求的价格弹性的大小。,Chapter 4,Slide 42,4.3 市场需求,需求的弧弹性弧弹性（Arc elasticity）计算
14、需求的某一段价格弹性。弧弹性公式为：,Chapter 4,Slide 43,4.3 市场需求,需求的弧弹性,Chapter 4,Slide 44,The Aggregate Demand For Wheat,The demand for U.S.wheat is comprised of domestic demand and export demand.,Chapter 4,Slide 45,An Example:,The Aggregate Demand For Wheat,The domestic demand for wheat is given by the equation:QDD
15、=1700-107PThe export demand for wheat is given by the equation:QDE=1544-176P,Chapter 4,Slide 46,The Aggregate Demand For Wheat,Domestic demand is relatively price inelastic(-0.2),while export demand is more price elastic(-0.4).,Chapter 4,Slide 47,The Aggregate Demand For Wheat,Chapter 4,Slide 48,Whe
16、at(million bushels/yr.),Price($/bushel),0,2,4,6,8,10,12,14,16,18,20,1000,2000,3000,4000,Consumer Surplus,Consumer Surplus The difference between the maximum amount a consumer is willing to pay for a good and the amount actually paid.,Chapter 4,Slide 49,Consumer Surplus,Chapter 4,Slide 50,Consumer Su
17、rplus 6+5+4+3+2+1=21,Rock Concert Tickets,Price($perticket),2,3,4,5,6,13,0,1,14,15,16,17,18,19,20,Consumer Surplus,The stepladder demand curve can be converted into a straight-line demand curve by making the units of the good smaller.,Chapter 4,Slide 51,Consumer Surplus,Chapter 4,Slide 52,Consumer S
18、urplusfor the Market Demand,Rock Concert Tickets,Price($perticket),2,3,4,5,6,13,0,1,14,15,16,17,18,19,20,Consumer Surplus,Combining consumer surplus with the aggregate profits that producers obtain we can evaluate:1)Costs and benefits of different market structures2)Public policies that alter the be
19、havior of consumers and firms,Chapter 4,Slide 53,The Value of Clean Air,Air is free in the sense that we dont pay to breathe it.The Clean Air Act was amended in 1970.Question:Were the benefits of cleaning up the air worth the costs?,Chapter 4,Slide 54,An Example:,The Value of Clean Air,People pay mo
20、re to buy houses where the air is clean.Data for house prices among neighborhoods of Boston and Los Angeles were compared with the various air pollutants.,Chapter 4,Slide 55,Valuing Cleaner Air,Chapter 4,Slide 56,Network Externalities,Up to this point we have assumed that peoples demands for a good
21、are independent of one another.If fact,a persons demand may be affected by the number of other people who have purchased the good.,Chapter 4,Slide 57,Network Externalities,If this is the case,a network externality exists.Network externalities can be positive or negative.,Chapter 4,Slide 58,Network E
22、xternalities,A positive network externality exists if the quantity of a good demanded by a consumer increases in response to an increase in purchases by other consumers.Negative network externalities are just the opposite.,Chapter 4,Slide 59,Network Externalities,The Bandwagon EffectThis is the desi
23、re to be in style,to have a good because almost everyone else has it,or to indulge in a fad.This is the major objective of marketing and advertising campaigns(e.g.toys,clothing).,Chapter 4,Slide 60,Positive NetworkExternality:Bandwagon Effect,Chapter 4,Slide 61,Quantity(thousands per month),Price($p
24、er unit),Positive NetworkExternality:Bandwagon Effect,Chapter 4,Slide 62,Demand,Quantity(thousands per month),Price($per unit),D20,20,40,60,80,100,D40,D60,D80,D100,The market demandcurve is found by joiningthe points on the individual demand curves.It is relativelymore elastic.,Positive NetworkExter
25、nality:Bandwagon Effect,Chapter 4,Slide 63,Demand,Quantity(thousands per month),Price($per unit),D20,20,40,60,80,100,D40,D60,D80,D100,Pure PriceEffect,48,Suppose the price fallsfrom$30 to$20.If there were no bandwagon effect,quantity demanded wouldonly increase to 48,000,$20,$30,Positive NetworkExte
26、rnality:Bandwagon Effect,Chapter 4,Slide 64,Demand,Quantity(thousands per month),Price($per unit),D20,20,40,60,80,100,D40,D60,D80,D100,Pure PriceEffect,$20,48,BandwagonEffect,But as more people buythe good,it becomes stylish to own it and the quantity demandedincreases further.,$30,Network Externali
27、ties,The Snob EffectIf the network externality is negative,a snob effect exists.The snob effect refers to the desire to own exclusive or unique goods.The quantity demanded of a“snob”good is higher the fewer the people who own it.,Chapter 4,Slide 65,Negative NetworkExternality:Snob Effect,Chapter 4,S
28、lide 66,Quantity(thousandsper month),Price($per unit),Negative NetworkExternality:Snob Effect,Chapter 4,Slide 67,Quantity(thousandsper month),2,4,6,8,The demand is less elastic and as a snob good its value is greatlyreduced if more people ownit.Sales decrease as a result.Examples:Rolex watches and l
29、ong 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,Network Externalities and the Demands for Computers and Fax Machines,Examples of Positive Feedback ExternalitiesMainframe computers:1954-1965Microsoft Windows PC operating syste
30、mFax-machines and e-mail,Chapter 4,Slide 68,Empirical Estimation of Demand,The most direct way to obtain information about demand is through interviews where consumers are asked how much of a product they would be willing to buy at a given price.,Chapter 4,Slide 69,Empirical Estimation of Demand,Pro
31、blemConsumers may lack information or interest,or be mislead by the interviewer.,Chapter 4,Slide 70,Empirical Estimation of Demand,In direct marketing experiments,actual sales offers are posed to potential customers and the responses of customers are observed.,Chapter 4,Slide 71,Empirical Estimation
32、 of Demand,The Statistical Approach to Demand EstimationProperly applied,the statistical approach to demand estimation can enable one to sort out the effects of variables on the quantity demanded of a product.“Least-squares”regression is one approach.,Chapter 4,Slide 72,Demand Data for Raspberries,Y
33、earQuantity(Q)Price(P)Income(I),Chapter 4,Slide 73,1988424101989720101990817101991131717199216101719931515171994191220199520920199622520,Empirical Estimation of Demand,Assuming only price determines demand:Q=a-bPQ=28.2-1.00P,Chapter 4,Slide 74,Estimating Demand,Chapter 4,Slide 75,Quantity,Price,0,5,
34、10,15,20,25,15,10,5,25,20,Estimating Demand,Chapter 4,Slide 76,Adjusting for changes in income,Empirical Estimation of Demand,For the demand equation:Q=a-bPElasticity:,Chapter 4,Slide 77,Estimating Elasticities,Empirical Estimation of Demand,Assuming:Price&income elasticity are constantThe isoelasti
35、c demand=The slope,-b=price elasticity of demandConstant,c=income elasticity,Chapter 4,Slide 78,Estimating Elasticities,Empirical Estimation of Demand,Using the Raspberry data:Price elasticity=-0.24(Inelastic)Income elasticity=1.46,Chapter 4,Slide 79,Estimating Elasticities,Empirical Estimation of D
36、emand,Substitutes:b2 is positiveComplements:b2 is negative,Chapter 4,Slide 80,Estimating Complements and Substitutes,The Demand for Ready-to-Eat Cereal,What Do You Think?Are Grape Nuts&Spoon Size Shredded Wheat good substitutes?,Chapter 4,Slide 81,The Demand for Ready-to-Eat Cereal,AnswerEstimated d
37、emand for Grape Nuts(GN)Price elasticity=-2.0Income elasticity=0.62Cross elasticity=0.14,Chapter 4,Slide 82,Summary,Individual consumers demand curves for a commodity can be derived from information about their tastes for all goods and services and from their budget constraints.Engel curves describe
38、 the relationship between the quantity of a good consumed and income.,Chapter 4,Slide 83,Summary,Two goods are substitutes if an increase in the price of one good leads to an increase in the quantity demanded of the other.They are complements if the quantity demanded of the other declines.,Chapter 4
39、,Slide 84,Summary,Two goods are substitutes if an increase in the price of one good leads to an increase in the quantity demanded of the other.They are complements if the quantity demanded of the other declines.The effect of a price change on the quantity demanded can be broken into a substitution e
40、ffect and an income effect.,Chapter 4,Slide 85,Summary,The market demand curve is the horizontal summation of the individual demand curves for all consumers.The percent change in quantity demanded that results from a one percent change in price determines elasticity of demand.,Chapter 4,Slide 86,Summary,There is a network externality when one persons demand is affected directly by the purchasing decisions of other consumers.A number of methods can be used to obtain information about consumer demand.,Chapter 4,Slide 87,End of Chapter 4,Individual andMarket Demand,
