微观经济学第08章-完全竞争市场分析

1、完全竞争市场分析第8章1竞争性企业的供应行为8.123利润的定义Profits are net revenues, orProfits = total sales total costs假设运用会计本钱，那么为会计利润；假设运用经济本钱，那么为经济利润。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，一切的要素都得到了应得的收入，资本也不例外。假设经济利润大于0，资本将获得超额收益。4profitPQsalaryinterestrent=-竞争性企业的行为Our analysis of perfectly competitive firm

2、s relies on 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.5利润最大化行为的阐明6完全竞争市场的特征Perfect competition is the world of price-takers. A perfectly competitive firm sel

3、ls a homogeneous 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.7阐明普通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)；自在进入和退出

4、 (free entry and exit)；完美和完全信息 (perfect or complete information)。8DDSSddPQpqindustryfirm价钱接受者9阐明行业的需求曲线不能由将行业中一切企业的需求曲线相加而来。回想一下：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。假设各企业消费的产品都一样，那么产品之间可以完全相互替代。10QddFirm OutputPDSQ*P*qpIndustry OutputHow would you describe the firms demand in terms o

5、f elasticity?a) Elastic b) Inelastic c) Perfectly elastic11边沿收益Marginal Revenue (MR) is the change in revenue that is generated by additional unit of sales.MR = Salesq+1 - SalesqMR = dR / dq12阐明边沿收益比较销售量为q1和销售量为q时的销售总额之差，而不是在销售量为q的根底上，再添加1单位销量的价钱。例如，销售量为30时的边沿收益，不能是卖出30件产品后，再多卖1件的价钱。13完全竞争市场的边沿收益So

6、what must be the relationship between the industry market price and the firms marginal revenue in a perfectly competitive industry?a) P MRb) P = MRc) P MC 时添加产量，MRMC 时添加产量，MRMC 时减少产量都可以减少亏损，当 MR=MC 时，亏损到达最小化。零利润和停产价钱22QuantityPrice, AC, MCMCACAVCMMShutdown pointZero-profit pointddPS23停产规那么The shutdo

7、wn point (停产点) comes where revenues just cover variable costs or where loses are equal to fixed costs.PMCACAVC24The higher the firms fixed costs, the more it has to lose by shutting down.固定本钱的重要性Which type of industry is more likely to incur such losses?(a) An industry with low fixed costs like coff

8、ee shops and dry cleaners(b) A capital-intensive industry with high fixed costs like automobiles and the airlines竞争性行业的供应行为8.225企业的供应曲线26QuantityPrice, AC, MCACAVCShutdown pointSupply curve市场供应曲线27Quantity AQuantity BTotal quantityPricePricePriceFirm As SupplyFirm Bs SupplyMarket SupplySS28阐明假设企业的供应

9、之间相互关联时，不能简单地将各个企业的供应相加来得到市场供应。在完全竞争的市场上，各个企业的供应之间可以以为是没有关系的。不同时期的价钱变化29QuantityQuantityPricePriceShort-Run EquilibriumLong-Run Equilibrium30长期供应曲线Industry quantityPriceQ=qThe firms use some scarce factors which prices will be affected.The firms use general inputs without affecting the prices of tho

10、se general inputs.假设利为正31CompetitiveIndustryFree entryPriceand Profits32假设利润为负CompetitiveIndustryFree exitPriceand Profits零利润长期平衡33CompetitiveIndustryFree to entryFree to exitP=MC=ACZero-profit信誉卡的高利率摘自美克雷格彼得森，克里斯刘易斯：第4版，第272-273页。信誉卡行业符合完全竞争市场的多数特征，经济实际想象，信誉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年代初的现实阐明，虽然其

11、他利率在下降，信誉卡的利率依然很高。1998年，信誉卡持有者的筹资费用普通为1314，而银行付给储蓄者和货币市场账户上的存款利率只需45。34信誉卡允许消费者在购物时不运用现金，假设款项在30天内支付，就不收筹资费用。在信誉卡持有者中，有一小半人在规定的一个月期限内实践上支付了筹资费用；另有1/4的人预期他们不会有需求支付利息的透支余额。因此，只需剩下的1/4的持卡者，这些人预期本人要支付筹资费用，因此往往是根据必需支付利率的高低来选择购买何种信誉卡。35因此，在为信誉卡账户规定利率时，银行就要特别留意经常运用信誉卡的那些人所带来的风险。而这些在信誉卡上大量支付筹资费用的人往往是一些拖欠风险较

12、高的消费者，他们无法按优惠条件在别处获得信誉，他们不擅长理财，或者他们的净资产相对很少。因此，为什么对信誉卡上的余额索取高利率？解释是在规定利率时必需思索这1/4的持卡人所带来的风险。36竞争性市场的特殊情况8.33738竞争市场的普通原那么DDSSQuantityPriceDDSSQuantityPriceDemand ruleSupply rule39不变本钱Constant-cost supplySSPQQuantityPriceEEDDDD40固定供应和经济租金SSPQQuantityPriceEEDDDDFixed supplyFactors with fixed supply ea

13、rn rent.41向后弯曲的供应曲线SSPQQuantityPriceEETLabor supply竞争性市场的效率和平等8.442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 competitive market. We can think of efficiency in at least two dimensions of market performance (绩效):

14、 allocative efficiency (配置效率) and productive efficiency (消费效率). 4344消费的有效性Productive efficiency occurs when price equals minimum average total cost.This holds when a competitive industry is in long run equilibrium.45配置的有效性Allocative efficiency is a slightly more difficult concept.You may encounter s

15、everal different definitions of allocative efficiency.One of the most cumbersome is Pareto Optimality (帕累托最优性).帕累托最优性假设没有能够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到达了帕累托最优Pareto Optimal 。46Vilfredo Pareto1848-1923消费能够性边境An economy is clearly inefficient if it operates inside the PPF and no one need suffer a dec

16、line in utility by moving to the PPF.Therefore, at a minimum, an efficient economy is on its PPF. 47GunsButterU消费能够性边境Nonetheless, allocative efficiency goes one step further and requires not only that the right mix of goods be produced but also that these goods be allocated among consumers to maxim

17、ize consumer satisfaction.48GunsButter49竞争性平衡的效率效率消费的效率配置的效率资源配置效率产品配置效率50完全竞争平衡时的效率完全竞争的长期平衡可以同时满足：消费的效率和配置的效率包括配置资源和配置产品。证明思绪：消费的社会边沿利益是多少？消费的社会边沿本钱是多少？比较社会的边沿利益与边沿本钱，假设相等，那么社会利益最大化，也就是到达最优，或最有效率。净经济所得51P*ABEOQ*PP消费付出的总本钱(负成效)为AEQ*O面积，得到的总成效为BEQ*O面积，净经济收益为BEA面积。FFMU = DD假设规模扩展到F_F，经济收益减少。MC = SS52

18、众多消费者的平衡QuantityQuantityQuantityPricePricePricePerson APerson BIndustryP*53需求曲线反映社会的利益需求曲线反映了消费者的边沿成效。在完全竞争市场中，一切消费者都按平衡价钱支付，因此，平衡价钱等于一切消费者的边沿成效，即反映了社会的利益。54众多消费者的平衡QuantityQuantityQuantityPricePricePriceFirm AFirm BIndustryP*55供应曲线反映了社会的本钱供应曲线反映了消费者的边沿本钱。在完全竞争市场中，一切消费者都按平衡价钱得到补偿，因此，平衡价钱等于一切消费者的边沿本钱

19、，即反映了社会的本钱。56社会利益等与社会本钱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 social costs. Marginal Cost = Margina

20、l BenefitAt 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 utility. Therefore, MU or P mus

21、t equal MC.57众多市场的平衡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.58P = MC59边沿本钱定价的中心作用Only when prices are equal to marginal

22、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.60真实的世界There are two important areas where markets fail to achieve a

23、 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 or accepta

24、ble.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.6162外部性Externalities arise when some of the side effects of production or consumption

25、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 sell.

26、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.6364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 (使详细化)

27、 in productive and allocative efficiency. Yet still, there are several problems.65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，假设他改动了收入分配，那么他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方式。66宏大的收入差别可以是有效的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

28、 and wealth, While the results can be a perfectly efficient outcome.EFFICIENT OR EQUITY67什么样的结果更公平?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

29、box - or revolutionaries 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 normative policy debates.68为什么研讨完全竞争?Perfect competition gives us a benchmark against which to meas