1、完全竞争市场分析第8章竞争性企业的供给行为8.1利润的定义Profits are net revenues,orProfits=total sales total costs若使用会计成本，则为会计利润；若使用经济成本，则为经济利润。经济利润等于0，并不表示资本没有收入。劳动得到了应得的工资，资本得到了应得的利息，土地得到了应得的租金，所有的要素都得到了应得的收入，资本也不例外。如果经济利润大于0，资本将获得超额收益。profitPQsalaryinterestrent=-竞争性企业的行为 Our analysis of perfectly competitive firms relies o
2、n two key assumptions.First,we will assume that our competitive firm maximizes profits.Second,we reiterate that perfect competition is a world of atomistic firms who are price-takers.利润最大化行为的说明完全竞争市场的特征 Perfect competition is the world of price-takers.A perfectly competitive firm sells a homogeneous
3、 product(one identical to the product sold by others in the industry).The firm is so small relative to its market that it cannot affect the market price;it simply takes the price as given.说明 一般教材关于完全竞争的假设：无数的买者与卖者(numerous buyers and sellers)；产品没有区别(homogeneous products)；自由进入和退出(free entry and exit)
4、；完美和完全信息(perfect or complete information)。DDSSddPQpqindustryfirm价格接受者说明 行业的需求曲线不能由将行业中所有企业的需求曲线相加而来。回忆一下：市场的需求曲线由个人的需求曲线横向加总得到。一个产品的需求弹性与该产品的替代品多少或替代的难易程度相关。如果各企业生产的产品都一样，那么产品之间可以完全相互替代。How would you describe the firms demand in terms of elasticity?边际收益 Marginal Revenue(MR)is the change in revenue t
5、hat is generated by additional unit of sales.MR=Salesq+1-SalesqMR=dR/dq说明 边际收益比较销售量为q1和销售量为q时的销售总额之差，而不是在销售量为q的基础上，再增加1单位销量的价格。例如，销售量为30时的边际收益，不能是卖出30件产品后，再多卖1件的价格。完全竞争市场的边际收益 So what must be the relationship between the industry market price and the firms marginal revenue in a perfectly competitive
6、 industry?P=MR完全竞争市场边际收益图示增加一单位销售增加的收益=边际收益=价格P价格销售量利润最大化条件 Maximum profit will occur when output is at that level where the firms marginal revenue is equal to its marginal cost.At the maximum-point:MR=MCMax =R(q)-C(q)利润最大化条件的说明产出变化收益损失利润变化增加 1 单位边际收益边际成本MRMC减少 1 单位边际成本边际收益MCMR因此，当 MRMC 时增加产量，MRMC 时
7、增加产量，MRMC 时减少产量都可以减少亏损，当 MR=MC 时，亏损达到最小化。零利润和停产价格QuantityPrice,AC,MCMCACAVCMMShutdown pointZero-profit pointddPS停产规则 The shutdown point(停产点)comes where revenues just cover variable costs or where loses are equal to fixed costs.PMCACAVC The higher the firms fixed costs,the more it has to lose by shut
8、ting down.固定成本的重要性 Which type of industry is more likely to incur such losses?(a)An industry with low fixed costs like coffee shops and dry cleaners(b)A capital-intensive industry with high fixed costs like automobiles and the airlines竞争性行业的供给行为8.2企业的供给曲线QuantityPrice,AC,MCACAVCShutdown pointSupply
9、curve市场供给曲线Quantity AQuantity BTotal quantityPricePricePriceFirm As SupplyFirm Bs SupplyMarket SupplySS说明 如果企业的供给之间相互关联时，不能简单地将各个企业的供给相加来得到市场供给。在完全竞争的市场上，各个企业的供给之间可以认为是没有关系的。不同时期的价格变化QuantityQuantityPricePriceShort-Run EquilibriumLong-Run Equilibrium长期供给曲线Industry quantityPriceQ=qThe firms use some
10、scarce factors which prices will be affected.The firms use general inputs without affecting the prices of those general inputs.如果利为正CompetitiveIndustryFree entryPriceand Profits如果利润为负CompetitiveIndustryFree exitPriceand Profits零利润长期均衡CompetitiveIndustryFree to entryFree to exitP=MC=ACZero-profit信用卡的
11、高利率信用卡的高利率摘自美克雷格彼得森，克里斯刘易斯：管理经济学第4版，第272-273页。信用卡行业符合完全竞争市场的多数特征，经济理论设想，信用卡发行者之间的竞争会驱使利率下降。但20世纪80年代和90年代初的事实表明，尽管其他利率在下降，信用卡的利率仍然很高。1998年，信用卡持有者的筹资费用一般为1314，而银行付给储蓄者和货币市场账户上的存款利率只有45。信用卡允许消费者在购物时不使用现金，如果款项在30天内支付，就不收筹资费用。在信用卡持有者中，有一小半人在规定的一个月期限内实际上支付了筹资费用；另有1/4的人预期他们不会有需要支付利息的透支余额。因此，只有剩下的1/4的持卡者，这
12、些人预期自己要支付筹资费用，因而往往是根据必须支付利率的高低来选择购买何种信用卡。因此，在为信用卡账户规定利率时，银行就要特别注意经常使用信用卡的那些人所带来的风险。而这些在信用卡上大量支付筹资费用的人往往是一些拖欠风险较高的消费者，他们无法按优惠条件在别处取得信用，他们不善于理财，或者他们的净资产相对很少。因此，为什么对信用卡上的余额索取高利率？解释是在规定利率时必须考虑这1/4的持卡人所带来的风险。竞争性市场的特殊情况8.3竞争市场的一般原则DDSSQuantityPriceDDSSQuantityPriceDemand ruleSupply rule不变成本Constant-cost s
13、upplySSPQQuantityPriceEEDDDD固定供给和经济租金SSPQQuantityPriceEEDDDDFixed supplyFactors with fixed supply earn rent.向后弯曲的供给曲线SSPQQuantityPriceEETLabor supply竞争性市场的效率和平等8.4效率的概念 The importance of this conclusion about long run equilibrium lies in its implications(含义)for the efficiency of the perfectly compet
14、itive market.We can think of efficiency in at least two dimensions of market performance(绩效):allocative efficiency(配置效率)and productive efficiency(生产效率).生产的有效性 Productive efficiency occurs when price equals minimum average total cost.This holds when a competitive industry is in long run equilibrium.配
15、置的有效性 Allocative efficiency is a slightly more difficult concept.You may encounter several different definitions of allocative efficiency.One of the most cumbersome is Pareto Optimality(帕累托最优性).帕累托最优性 如果没有可能让一些人好起来却不使另一些人坏下去，那么这时的资源配置就达到了帕累托最优（Pareto Optimal）。Vilfredo Pareto1848-1923生产可能性边界 An econo
16、my is clearly inefficient if it operates inside the PPF and no one need suffer a decline in utility by moving to the PPF.Therefore,at a minimum,an efficient economy is on its PPF.生产可能性边界 Nonetheless,allocative efficiency goes one step further and requires not only that the right mix of goods be prod
17、uced but also that these goods be allocated among consumers to maximize consumer satisfaction.竞争性均衡的效率效率生产的效率配置的效率资源配置效率产品配置效率完全竞争均衡时的效率 完全竞争的长期均衡可以同时满足：生产的效率和配置的效率（包括配置资源和配置产品）。证明思路：生产的社会边际利益是多少？生产的社会边际成本是多少？比较社会的边际利益与边际成本，如果相等，则社会利益最大化，也就是达到最优，或最有效率。净经济所得P*ABEOQ*PP生产付出的总成本(负效用)为AEQ*O面积，得到的总效用为BEQ*
18、O面积，净经济收益为BEA面积。FFMU=DD若规模扩大到F_F，经济收益减少。MC=SS众多消费者的均衡QuantityQuantityQuantityPricePricePricePerson APerson BIndustryP*需求曲线反映社会的利益 需求曲线反映了消费者的边际效用。在完全竞争市场中，所有消费者都按均衡价格支付，因此，均衡价格等于所有消费者的边际效用，即反映了社会的利益。众多生产者的均衡QuantityQuantityQuantityPricePricePriceFirm AFirm BIndustryP*供给曲线反映了社会的成本 供给曲线反映了生产者的边际成本。在完全
19、竞争市场中，所有生产者都按均衡价格得到补偿，因此，均衡价格等于所有生产者的边际成本，即反映了社会的成本。社会利益等与社会成本 The supply curve reflects the costs of production and therefore must reflect the social costs of producing the product.In a perfectly competitive market,equilibrium occurs where supply intersects(相交)demand so that social benefits equal s
20、ocial costs.Marginal Cost=Marginal Benefit At this equilibrium point,the marginal cost of production exactly equals the marginal benefit or utility of consumption.We know this to be true because from consumer theory,we know that consumers choose purchases up to the point where price equals marginal
21、utility.Therefore,MU or P must equal MC.众多市场的均衡 Utility-maximizing consumers spread their dollars among different goods until the marginal utility of the last dollar is equalized for each good consumed.Then the MUs,which are equal to the Ps,will be equal to the MCs.边际成本定价的中心作用 Only when prices are e
22、qual to marginal costs is the economy squeezing the maximum output and satisfaction from its scarce resources of land,labor,and capital.Only when price is equal to marginal cost for all firms will society be on its production-possibility frontier.真实的世界 There are two important areas where markets fai
23、l to achieve a social optimum.First,markets may be inefficient in situations where pollution or other externalities are present or when there is imperfect competition or information.Second,the distribution of incomes under competitive markets,even when it is efficient,may not be socially desirable o
24、r acceptable.不完全竞争 When a firm has market power in a particular market(say it has a monopoly because of a patented drug or a local electricity franchise),the firm can raise the price of its product above its marginal cost.外部性 Externalities arise when some of the side effects of production or consump
25、tion are not included in market prices.Not all externalities are harmful.Some are beneficial,such as the externalities that come from knowledge-generating activities.不完全信息 The invisible-hand theory assumes that buyers and sellers have complete information about the goods and services they buy and se
26、ll.Firms are assumed to know about all the production functions for operating in their industry.Consumers are presumed to know about the quality and prices of goods.完全竞争的两大优点 Weve proven that a perfectly competitive market yields the most efficient use and allocation of resources as embodied(使具体化)in
27、 productive and allocative efficiency.Yet still,there are several problems.公平问题 市场竞争的结果可以是有效率的，但未必是公平的。也就是说，如果你改变了收入分配，那么你就得到了一个不同的有效率的资源配置，同时也伴随一个不同的消费模式。巨大的收入差异可以是有效的 In a world of perfect competition,the system of prices and markets may be one in which a few people have most of the income and wea
28、lth,While the results can be a perfectly efficient outcome.EFFICIENT OR EQUITY什么样的结果更公平?That is a normative or prescriptive question,one that asks the question:“what should be?”Deciding such questions are more properly the domain of politicians and philosophers and voters at the ballot box-or revolu
29、tionaries in the jungle实证经济学 The more proper role of the economist is positive or descriptive.Positive economics can offer great insights about how different types of government policies can affect the distribution of income and consumption.Therefore,positive economic analysis is essential in many n
30、ormative policy debates.为什么研究完全竞争?Perfect competition gives us a benchmark against which to measure how our other three market structures perform:monopoly(垄断),oligopoly(寡头),and monopolistic competition(垄断竞争).It also gives us appropriate guidance as to when and how to intervene in the market to corre
31、ct market failures as well as how to measure our success or failure at doing so.结束结束利润最大化行为准则的说明 实际中企业的行为取决于企业的控制权掌握在所有者还是经营者手里。假定企业追求最大利润的理由：利润最大化行为准则便于理论分析；如果市场竞争机制是完善的，追求利润的企业更有可能在市场竞争中生存。规模(产量)利润O计划利润利润为正，生存利润为负，淘汰 只要市场的竞争淘汰机制是完善的，即便经营者可以完全控制企业，也不敢一味追求大的规模。经济学的假定需要合理性吗？如果一个理论的假定（假设）不合理，我们能够得出合理的
32、结论吗？我们的假定有可能都合理吗？经济学家的分歧 经济学家关于经济学的假定是否应该具有“经验内容”的看法是不一致的。有的经济学家认为，一个能够有效地解释经济现象的假定应该或多或少具有经验内容。有的经济学家认为，假定无须包含经验内容。一个好的假定往往是不合理的。张五常的张五常的“白痴与汽油站白痴与汽油站”有一群人，每个都是白痴。经济学者却假设他们每个人明智地争取最大的利益。事实上，这个经济假设显然是错了。这些白痴听说汽油站很好玩，於是每个人都开办油站了。因为是白痴，他们之中有些把油站建在荒山之上，有些建在密林之中，也有些建在海上的，但有几个却糊里糊涂地把汽油站建在公路旁。过不了多久，适者生存，不适者淘汰，只有在公路旁建油站的白痴能生存。事实上，白痴是不知自己所为的。经济学者假设他们懂得怎样争取最大利益，显然是错了的，但留存下来的油站，却刚刚与争取最大利益的假设不谋而合。假设白痴懂得怎样争取利益虽然是错了，但却准确地推测了白痴建油站在公路旁的行为，这些行为於是就被解释了。说他们不知所为，所以油站不会建在最有利可图的地方，是谬论。
