LECTURE 5 竞争性市场与一般均衡(平狄克,微观经济学-厦门大学,王瑞芳).ppt

微观经济学 (平狄克，鲁宾费尔德，第四版) LECTURE 5 竞争性市场与一般均衡 1 一、竞争性市场 2 完全竞争市场 n完全竞争市场的条件： n价格接受者： 单个厂商产出占市场总供给的很小份额，因此无法影响市 场价格； 单个消费者购买的产品占市场需求的很小份额，因此无法 影响市场价格。 n产品同质性： 所有厂商的产品是完全可替代的。 n自由进出入： 买方可无成本地从一个厂商转向另一个厂商； 厂商可无成本进入退出某个产业。 3 财富效应 n消费者剩余和厂商剩余： n在一个竞争性市场中的各自份额 ，PP5； n政府政策的财富效应： n因政府干预市场而导致的收益或损失，通过消费者 剩余和厂商剩余的增减得到衡量。 n政府制定价格高限，产生无谓损失。PP6 当消费者的需求具有足够低的弹性时，政府限价在降低厂 商剩余的同时，还可能给消费者带来消费者剩余的绝对下 降 。PP7 n政府制定价格低限，同样产生无谓损失。PP8 4 Producer Surplus Between 0 and Q0 producers receive a net gain from selling each product- producer surplus. Consumer Surplus Consumer and Producer Surplus Quantity 0 Price S D 5 Q0 Consumer C 10 7 Consumer BConsumer A Between 0 and Q0 consumers A and B receive a net gain from buying the product- consumer surplus 5 The loss to producers is the sum of rectangle A and triangle C. Triangle B and C together measure the deadweight loss. B A C The gain to consumers is the difference between the rectangle A and the triangle B. Deadweight Loss Change in Consumer and Producer Surplus from Price Controls Quantity Price S D P0 Q0 Pmax Q1Q2 Suppose the government imposes a price ceiling Pmax which is below the market-clearing price P0. 6 B A Pmax C Q1 If demand is sufficiently inelastic, triangle B can be larger than rectangle A and the consumer suffers a net loss from price controls. Example Oil price controls and gasoline shortages in 1979 S D Effect of Price Controls When Demand Is Inelastic Quantity Price P0 Q2 7 P2 Q3 A B C Q2 What would the deadweight loss be if QS = Q2? When price is regulated to be no lower than P2 only Q3 will be demanded. The deadweight loss is given by triangles B and C Welfare Loss When Price Is Held Above Market-Clearing Level Quantity Price S D P0 Q0 8 竞争性市场的效率 n市场失灵： n外部性： 市场价格无法反映的成本收益内容； n信息缺失： 不完美信息导致消费者无法做出效用最大化决策。 n在这种情况下政府干预市场将有可能增进效率 ；相反，在市场并未失灵的情况下政府干预将 导致市场效率降低和无谓损失。 9 B A The change in producer surplus will be A - C - D. Producers may be worse off. C D Price Minimum Quantity Price S D P0 Q0 Pmin Q3Q2 If producers produce Q2, the amount Q2 - Q3 will go unsold. 10 B The deadweight loss is given by triangles B and C. C A wmin L1L2 Unemployment Firms are not allowed to pay less than wmin. This results in unemployment. S D w0 L0 The Minimum Wage L w 11 价格支持和生产配额 n价格支持： n政府制定高于均衡价格的支持价格，再由政府 购买过剩的供给； n这一政策常与减产或限产的激励政策相结合。 n政府成本：Ps(Q2-Q1) n无谓损失：消费者剩余+厂商剩余-政府成本 =D-(Q2-Q1)ps 12 B D A To maintain a price Ps the government buys quantity Qg . The change in consumer surplus = -A - B, and the change in producer surplus is A + B + D D + Qg Qg Price Supports Quantity Price S D P0 Q0 Ps Q2Q1 13 D + Qg Qg B A Price Supports Quantity Price S D P0 Q0 Ps Q2Q1 The cost to the government is the speckled rectangle Ps(Q2-Q1) D Total Welfare Loss Total welfare loss D-(Q2-Q1)ps 14 价格支持和生产配额 n生产配额 ： n通过限制供给来提高商品价格。 n对农民而言，价格支持和生产配额无差别，都 使他们获得A+B+D的额外厂商剩余； n但对政府而言，两种政策就是有差别的，哪一 种政策代价更大，应比较B+C+D（配额）和 Ps(Q2-Q1)（价格支持）的大小。 15 B A C D Supply Restrictions Quantity Price D P0 Q0 S PS S Q1 Ps is maintained with and incentive Cost to government = B + C + D 16 Supply Restrictions B A Quantity Price D P0 Q0 PS S S D C n = A - C + B + C + D = A + B + D. nThe change in consumer and producer surplus is the same as with price supports. n = -A - B + A + B + D - B - C - D = -B - C. 17 进口限额和关税 n目的： n使进口商品国内价格高于国际价格，从而达到 限制进口的目的。 n进口配额或关税带来的福利损失： n国内厂商价格上涨，厂商剩余增加A； n消费者剩余损失由两部分构成，因国内商品价 格上升而导致的损失和因进口商品价格上升而 导致的损失：A+B+C+D 18 QSQD PW Imports A BC By eliminating imports, the price is increased to PO. The gain is area A. The loss to consumers A + B + C, so the deadweight loss is B + C. Import Tariff or Quota That Eliminates Imports Quantity Price How high would a tariff have to be to get the same result? D P0 Q0 S In a free market, the domestic price equals the world price PW. 19 D CB QSQDQSQD A P* Pw Import Tariff or Quota (general case) Quantity Price D S nThe increase in price can be achieved by a quota or a tariff. nArea A is again the gain to domestic producers. nThe loss to consumers is A + B + C + D. 20 Import Tariff or Quota (general case) nIf a tariff is used the government gains D, so the net domestic product loss is B + C. nIf a quota is used instead, rectangle D becomes part of the profits of foreign producers, and the net domestic loss is B + C + D. D CB QSQDQSQD A P* Pw Quantity D S Price 21 征税或补贴的影响 n征税： n买方价格卖方价格 n从量税征税后必须满足四个条件： 销售量和购买价格位于需求曲线上，QD = QD(Pb) 销售量和销售价格位于供给曲线上，QS = QS(Ps) 需求量=供给量，QD = QS 购买价与销售价之差为税收，Pb - PS = tax 22 D S B D A Buyers lose A + B, and sellers lose D + C, and the government earns A + D in revenue. The deadweight loss is B + C. C Incidence of a SpecificTax Quantity Price P0 Q0Q1 PS Pb t Pb is the price (including the tax) paid by buyers. PS is the price sellers receive, net of the tax. The burden of the tax is split evenly. 23 征税或补贴的影响 n征税： n税收影响取决于供给和需求弹性； n一般来说，如Ed/Es较小，税负主要由买方承 担，反之则由卖方承担。 n转嫁因子：ES/(ES - Ed) 转嫁因子趋近于1，税负主要由消费者承担； 转嫁因子趋近于0，税负主要由厂商承担。 24 Impact of a Tax Depends on Elasticities of Supply and Demand Quantity Quantity PricePrice S D S D Q0 P0 P0 Q0 Q1 Pb PS t Q1 Pb PS t Burden on BuyerBurden on Seller 25 征税或补贴的影响 n补贴： n补贴可视为负税收，分析方法与上面相同。 n在此种情况下，买方价格 m*. 77 Refundable Deposits Amount of Glass $ D Price falls to P and the amount of recycled glass increases to M*. Sv Sr S The supply of glass is the sum of the supply of virgin glass (Sr) and the supply of recycled glass (Sr). M1 P Without refunds the price of glass is P and Sr is M1. Sr S P M* With refunds Sr increases to Sr and S increases to S. 78 外部性和产权 n产权是描述人们或厂商可以对他们的财产做什么 的法律规则。 n议价与经济效率 n当受外部性影响的群体较少并且产权良好界定时，经 济效率将在没有政府干预的情况下实现。 n科斯定理：当各方能够无成本地讨价还价并对大家都 有利时，无论产权如何界定，最终结果都将是有效率 的。 n有成本的议价 n议价要求清晰界定的产权和规则。 n诉诸法律：对损害起诉 n对损害进行法律诉讼导致有效率的结果。 79 三、公共物品和公共资源 n私人物品： n排他性：只有对商品支付价格的人才能使用该商品； n竞用性：如某人已使用了某个商品，则其他人不能再 同时使用该商品。 n公共物品： n不具有排他性与竞用性的物品； n公共资源： n不具有排他性但却具有竞用性的物品。 80 共有资源 n每个人都可免费获得的资源；该资源倾向 于被过渡使用。 n解决办法：界定私有产权。 81 Common Property Resources Fish per Month Benefits, Costs ($ per fish) Demand However, private costs underestimate true cost. The efficient level of fish/month is F* where MSC = MB (D) Marginal Social Cost F* Private Cost FC Without control the number of fish/month is FC where PC = MB. 82 公共产品 n公共产品的特点： n非竞争性：给定任何生产水平，向一个额外消费者提 供该商品的边际成本为0； n非排他性：无法禁止人们消费该种商品。 n注意：并非所有政府生产的产品都是公共产品。 n公