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1、第三章 市场与福利,前面说明了供给和需求的力量如何决定了物品和劳务的价格和销售量，本章将分析这些市场配置是否令人满意的问题。福利经济学（welfare economics）：研究资源配置如何影响经济福利的一门学问。,一、消费者剩余（consumer surplus）,买者愿意为某种物品支付的最高量称为支付意愿（willingness to pay）。买者愿意为一种物品支付的量减去买者为此实际支付的量为消费者剩余。消费者剩余衡量了买者从一种物品中得到的自己感觉到的利益。衡量方法：需求曲线以下和价格以上的面积衡量市场的消费者剩余。,第一节 消费者、生产者与市场效率,价格如何影响消费者剩余,数量,价
2、格,0,需求,原来的消费者剩余,二、生产者剩余（producer surplus),卖者出售一种物品得到的量减去卖者的成本。衡量买者从参与市场中得到的利益。衡量方法：供给曲线以上和价格以下的面积衡量市场的生产者剩余。,价格如何影响生产者剩余,数量,价格,0,供给,原来的生产者剩余,市场均衡时的消费者剩余和生产者剩余,价格,均衡价格,0,数量,均衡数量,A,供给,C,B,需求,D,E,生产者剩余,消费者剩余,P,0,Q,均衡数量,S,D,卖者的成本,买者的评价,买者的评价,卖者的成本,买者的评价大于卖者的成本,买者的评价小于卖者的成本,三、均衡数量的效率,市场结果,（1）自由市场把物品的供给分配
3、给对这些物品评价最高的买者。（2）自由市场将物品的需求分配给能够以最低成本生产这些物品的卖者。（3）自由市场生产出使消费者剩余和生产者剩余的总和最大的物品量。总之，市场结果使消费者剩余和生产者剩余之和达到最大化。即均衡的结果是资源的有效配置。但是，在存在市场势力或外部性等市场失灵的情况下，市场不能有效地配置资源。,第二节 税赋的福利分析,Q,0,P,D,S,Q1,Q2,税赋减少的消费者剩余=B+C 税赋减少的生产者剩余=D+E,税赋收入=B+D,无谓损失=(C+E),无谓损失：税收引起的总剩余的减少。图中（C+E）。,税收引起的无谓损失是因为它使买者和卖者不能实现某些贸易的好处,Q,0,P,D
4、,S,Q1,PB,P1没有税收时的价格,PS,Q2,无谓损失,Q,P,D,S,0,(a)缺乏弹性的供给,决定无谓损失的因素供给和需求的价格弹性,税收扭曲与弹性,Q,P,D,S,0,(b)富有弹性的供给,税收扭曲与弹性,Q,P,D,S,0,(c)缺乏弹性的需求,税收扭曲与弹性,Q,P,D,S,0,(d)富有弹性的需求,供给和需求的弹性越大，税收的无谓损失也越大。,无谓损失和税收收入随税收规模的变动,PB,Q,Q2,0,P,Q1,D,S,PS,(a)小额税,D,S,PB,Q,Q2,0,P,Q1,PS,(b)中额税,PB,Q,Q2,0,P,Q1,D,S,PS,(c)大额税,无谓损失随税收规模的变动,
5、无谓损失,0,税收规模,税收收入随税收规模的变动,税收收入,0,税收规模,第三节 国际贸易与福利,1.国际贸易如何影响经济福利？2.在各国的经济贸易中谁受益？谁受损？3.如何比较利益和损失？,没有贸易时的均衡,0,数量,均衡数量,国内供给,国内需求,生产者剩余,消费者剩余,一、决定贸易的因素,世界价格和比较优势,1.世界价格：一种物品在世界市场上所通行的价格。2.比较贸易之前的世界价格和国内价格可以知道一国在一种物品的生产上是否有比较优势。3.各国之间贸易建立在比较优势的基础上。,0,纺织品数量,国内需求,出口国的国际贸易,国内供给,二、贸易的赢家和输家,0,Quantity,of Steel
6、,Worldprice,Domesticdemand,贸易对出口国福利的影响,Domesticsupply,Price after trade,Price before trade,A,B,C,D,Exports,出口国国际贸易后的福利变化,面积 D表示总剩余的增加，并代表贸易的利益,贸易前,贸易后,变动,消费者剩余,A+B,A,-B,生产者剩余,C,B+C+D,+(B+D),总剩余,A+B+C,A+B+C+D,+D,结论：,1.当一国允许贸易并成为一种物品的出口者时，国内该物品生产者的状况变好，而国内该物品消费者的状况变坏。2.贸易增加了国家总体的经济福利。,进口国的国际贸易,0,纺织品数量
7、,国内供给,国内需求,贸易对进口国福利的影响,0,Quantity,of Steel,Domesticsupply,World Price,Domestic demand,Price after trade,Price before trade,A,B,C,D,Imports,进口国国际贸易的福利变化,面积D表示总剩余增加，并代表贸易的利益。,贸易前,贸易后,变动,消费者剩余,A,A+B+D,+(B+D),生产者剩余,B+C,C,-B,总剩余,A+B+C,A+B+C+D,+D,The analysis of an importing country yields two conclusions
8、:,1.Domestic producers of the good are worse off,and domestic consumers of the good are better off.2.Trade raises the economic well-being of the nation as a whole because the gains of consumers exceed the losses of producers.,The Gains and Losses from Free International Trade,The gains of the winner
9、s exceed the losses of the losers.The net change in total surplus is positive.,Tariffs,Tariffs are taxes on imported goods.Tariffs raise the price of imported goods above the world price by the amount of the tariff.,The Effects of a Tariff.（关税的影响）,0,Quantity,of Steel,Domestic supply,Domestic demand,
10、The Effects of a Tariff.,0,Quantity,of Steel,Domestic supply,Domestic demand,World price,Q1S,Q1D,Price without tariff,Imports without tariff,The Effects of a Tariff.,0,Quantity,of Steel,Domestic supply,Domestic demand,Tariff,World price,Q1S,Q2S,Q2D,Q1D,Price without tariff,Price with tariff,Imports
11、without tariff,Imports with tariff,The Effects of a Tariff.,0,Quantity,of Steel,Domestic supply,Domestic demand,Tariff,World price,Q1S,Q2S,Q2D,Q1D,Imports without tariff,Imports with tariff,The Effects of a Tariff.,0,Quantity,of Steel,Domestic supply,Domestic demand,Tariff,World price,Q1S,Q2S,Q2D,Q1
12、D,Imports without tariff,Imports with tariff,Price with tariff,Price without tariff,The Effects of a Tariff.,0,Quantity,of Steel,Domestic supply,Domestic demand,Tariff,World price,Q1S,Q2S,Q2D,Q1D,Price without tariff,Price with tariff,Imports without tariff,Imports with tariff,A,B,C,E,G,Changes in W
13、elfare from a Tariff,The area D+F shows the fall in total surplus and represents the deadweight loss of the tariff.,The Effects of a Tariff,A tariff reduces the quantity of imports and moves the domestic market closer to its equilibrium without trade.With a tariff,total surplus in the market decreas
14、es by an amount referred to as a deadweight loss.,Other Benefits of International Trade,Increased variety of goodsLower costs through economies of scaleIncreased competitionEnhanced flow of ideas（加强了思想交流）,三、各种限制贸易的观点（The Arguments for Restricting Trade）,Jobs（工作岗位论）National Security（国家安全论）Infant Indu
15、stry（幼稚产业论）Unfair Competition（不公平竞争论）Protection as a Bargaining Chip（作为讨价还价筹码的保护论）,Summary（内容提要）,The effects of free trade can be determined by comparing the domestic price without trade to the world price.A low domestic price indicates that the country has a comparative advantage in producing the g
16、ood and that the country will become an exporter.A high domestic price indicates that the rest of the world has a comparative advantage in producing the good and that the country will become an importer.,Summary,When a country allows trade and becomes an exporter of a good,producers of the good are
17、better off,and consumers of the good are worse off.When a country allows trade and becomes an importer of a good,consumers of the good are better off,and producers are worse off.,Summary,A tariff a tax on imports moves a market closer to the equilibrium than would exist without trade,and therefore r
18、educes the gains from trade.Import quotas（限额）will have effects similar to those of tariffs.,Summary,There are various arguments for restricting trade:protecting jobs,defending national security,helping infant industries,preventing（防止）unfair competition,and responding to foreign trade restrictions.Economists,however,believe that free trade is usually the better policy.,作业,解释概念：消费者剩余P165 6,
