In this chapter, look for the answers to these questions:

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0 Public Goods and Common Resources
11 Public Goods and Common Resources 公共物品与公共资源 This chapter is shorter than average. (In many other textbooks, a single chapter combines this material with externalities.) It’s also less analytically challenging than average, so most students find it less difficult – especially when covered immediately after the externalities chapter. Most instructors are able to cover this chapter in a single class session. This PowerPoint presentation includes a case study on Spam . This case study does not appear in the textbook.

1 In this chapter, look for the answers to these questions:
What are public goods? What are common resources? Give examples of each. Why do markets generally fail to provide the efficient amounts of these goods? How might the government improve market outcomes in the case of public goods or common resources? 什么是公共物品？什么是公共资源？各举出一些例子 为什么市场在提供这些物品的有效率数量上总是失败？ 在公共物品或公共资源上，政府怎么做才能改善市场结果？ 1

2 Introduction 我们消费许多无需支付价格的物品：公园，国防，清洁的空气与水 当物品没有价格时，正常分配资源的市场力量失效
We consume many goods without paying: parks, national defense, clean air & water. When goods have no prices, the market forces that normally allocate resources are absent. The private market may fail to provide the socially efficient quantity of such goods. One of the Ten Principles from Chapter 1: Governments can sometimes improve market outcomes. 我们消费许多无需支付价格的物品：公园，国防，清洁的空气与水 当物品没有价格时，正常分配资源的市场力量失效 私人市场可能不能提供有社会效率的这些物品的数量 第一章的十大原理之一： 政府有时可以改善市场结果 2

3 Important Characteristics of Goods
A good is excludable if a person can be prevented from using it. Excludable: fish tacos, wireless internet access Not excludable: FM radio signals, national defense A good is rival in consumption if one person’s use of it diminishes others’ use. Rival: fish tacos Not rival: An MP3 file of Kanye West’s latest single 一种物品具有排他性是指该物品具有的可以阻止一个人使用它的特性 排他性：炸玉米饼，无线网络接口 非排他性：调频广播信号，国防 一种物品具有消费中的竞争性 是指一个人使用该物品将减少 其他人对它的使用的特性 竞争性：炸玉米饼 非竞争性：MP3文件的Kanye West的最新单曲 3

4 The Different Kinds of Goods
Private goods: excludable, rival in consumption Example: food Public goods: not excludable, not rival Example: national defense Common resources: rival but not excludable Example: fish in the ocean Natural monopolies: excludable but not rival Example: cable TV 私人物品：在消费者既有排他性又有竞争性 例如：食品 公共物品：非竞争性，非排他性 例如：国防 公共资源：在消费中有竞争性，但没有排他性 例如：海洋中的鱼 自然垄断：在消费中有排他性，但没有竞争性 例如：有线电视 Using the two characteristics on the preceding slide, we can classify most goods in one of the four categories on this slide. As each example displays, explain why it belongs to its category/classification. E.g., food is a private good because: 1) It is excludable: you cannot have any unless you buy it. 2) It is rival in consumption: if you eat that fish taco, I won’t be able to eat it. 4

5 A C T I V E L E A R N I N G 1 Categorizing roads 道路的分类
A road is which of the four kinds of goods? Hint: The answer depends on whether the road is congested or not, and whether it’s a toll road or not. Consider the different cases. 道路是这四种物品中的哪一类？ 提示：答案取决于物品是否是拥挤的，以及它是否收费。考虑不同的情形 This brief exercise gives students practice applying the definitions of rival and excludable and the four different types of goods. Suggestion: Tell students they have 1-2 minutes to formulate an answer, then another 2 minutes to compare their answer with that of one student sitting near them. Then ask for students to volunteer their responses. If you’re pressed for time, you can safely omit this exercise. Students can get this information from a careful reading of the chapter. 5

6 A C T I V E L E A R N I N G 1 Answers
消费中的竞争性？仅当道路是拥挤的时候 排他性？仅当道路收费时 四种可能性： 不拥挤也不收费：公共物品 不拥挤但收费：自然垄断 拥挤但不收费：公共资源 供给也收费：私人物品 Rival in consumption? Only if congested. Excludable? Only if a toll road. Four possibilities: Uncongested non-toll road: public good Uncongested toll road: natural monopoly Congested non-toll road: common resource Congested toll road: private good 6

7 The Different Kinds of Goods
本章主要考察公共物品与公共资源 对两者而言，外部性的产生是由于有价值的东西没有价格 由于这些外部性，关于消费和生产的私人决策会引起无效率的资源配置 公共政策可以潜在地增进经济的福利 This chapter focuses on public goods and common resources. For both, externalities arise because something of value has no price attached to it. So, private decisions about consumption and production can lead to an inefficient outcome. Public policy can potentially raise economic well-being. 7

8 Public Goods 公共物品难以在私人市场上提供，这是因为搭便车者问题 搭便车者：得到一种物品的利益但避开为此付费的人
如果物品具有非排他性，人们就会有激励成为搭便车者。这是因为企业不能阻止不付费者消费该物品 结果：这种物品不会被生产，即使买者对于物品的集体评价要大于提供它的成本 Public goods are difficult for private markets to provide because of the free-rider problem. Free rider: a person who receives the benefit of a good but avoids paying for it If good is not excludable, people have incentive to be free riders, because firms cannot prevent non-payers from consuming the good. Result: The good is not produced, even if buyers collectively value the good higher than the cost of providing it. The textbook exposits these ideas using a simple example – a fireworks display in Smalltown, U.S.A. The Study Guide offers another example, in which the cost of installing a streetlight in a neighborhood is less than the collective benefits of the people who live on that street – yet, no one takes the initiative to provide it. 8

9 Public Goods 如果政府确信一种公共物品的总利益大于成本，它就可以提供该公共物品，并用税收收入对其进行支付，从而可以使每个人的状况变好 问题：衡量利益通常是困难的 成本—收益分析：比较提供一种公共物品的社会成本与社会收益的研究 成本-收益分析是不精确的，因此提供有效率的公共物品的难度要远远大于提供有效率的私人物品的难度 If the benefit of a public good exceeds the cost of providing it, govt should provide the good and pay for it with a tax on people who benefit. Problem: Measuring the benefit is usually difficult. Cost-benefit analysis: a study that compares the costs and benefits of providing a public good Cost-benefit analyses are imprecise, so the efficient provision of public goods is more difficult than that of private goods. 9

10 Some Important Public Goods
National defense Knowledge created through basic research Fighting poverty 国防 基础研究创造的知识 反贫困 10

11 Common Resources 与公共物品一样，公共资源也没有排他性 不能阻止搭便车者的使用 企业没有激励提供这种物品
Like public goods, common resources are not excludable. Cannot prevent free riders from using Little incentive for firms to provide Role for govt: seeing that they are provided Additional problem with common resources: rival in consumption Each person’s use reduces others’ ability to use Role for govt: ensuring they are not overused 与公共物品一样，公共资源也没有排他性 不能阻止搭便车者的使用 企业没有激励提供这种物品 政府的角色：确定它们的供给 公共资源的附加问题：消费中的竞争性 一个人的使用会减少另一个人对它的享用 政府的角色：确保它们不被过度使用 11

12 The Tragedy of the Commons公地悲剧
A parable that illustrates why common resources get used more than is socially desirable. Setting: a medieval town where sheep graze on common land. As the population grows, the # of sheep grows. The amount of land is fixed, the grass begins to disappear from overgrazing. The private incentives (using the land for free) outweigh the social incentives (using it carefully). Result: People can no longer raise sheep. 寓言说明了为什么公共资源的使用大于合意的水平 背景：一个中世纪小镇，大家在公地上放羊 镇上的人看增加，公地上的羊也在增加 土地的数量是固定的，由于过度放牧，土地上的青草开始减少 私人激励（免费使用土地）超过社会激励（有保护的使用） 结果：人们不能再放羊 12

13 The Tragedy of the Commons
The tragedy is due to an externality: Allowing one’s flock to graze on the common land reduces its quality for other families. People neglect this external cost, resulting in overuse of the land. 悲剧的产生是因为外部性：当一个家庭的羊群在公地上吃草时，它降低了其他家庭可以得到的土地质量 人们不考虑这种外部成本，导致了对公地的过度使用 13

14 A C T I V E L E A R N I N G 2 Policy options for common resources
小镇桑的人们（或者他们的政府）能为防止这种悲剧做点什么？ 尝试想出两种或三种办法 What could the townspeople (or their government) have done to prevent the tragedy? Try to think of two or three options. If you’re pressed for time, you can safely omit this exercise. Its contents will be covered in a subsequent slide, and students can learn this material from a careful reading of the chapter. This exercise has several objectives: 1) It gets students to anticipate the policy solutions to the common resource problem based on what they have just learned about the problem. 2) After giving students a big hint on the preceding slide, it tests to see whether they make the connection between the common resource problem and the policies to deal with negative externalities they learned in the preceding chapter. To get through this activity quickly, display the question, give students a quiet moment to formulate their responses, then ask for students to share their answers. If you can spare an extra couple of minutes, have them work in pairs – two minutes should suffice – and then ask students to share their answers with the class. 14

15 A C T I V E L E A R N I N G 2 Answers
对土地的使用征收一种矫正性税收，使“外部性内部化” 管制公地的使用（“命令与控制”的方法） 拍卖使用土地的权利 把土地分成小块，并出售给家庭；每个家庭将会有不过度放牧的激励 Impose a corrective tax on the use of the land to “internalize the externality.” Regulate use of the land (the “command-and-control” approach). Auction off permits allowing use of the land. Divide the land, sell lots to individual families; each family will have incentive not to overgraze its own land. All of these policy options have been used in modern times to deal with the common resource problem. The following slide shows a few examples. 15

16 Policy Options to Prevent Overconsumption of Common Resources 防止公共资源过度消费的政策选择
Regulate use of the resource Impose a corrective tax to internalize the externality example: hunting & fishing licenses, entrance fees for congested national parks Auction off permits allowing use of the resource example: spectrum auctions by the U.S. Federal Communications Commission If the resource is land, convert to a private good by dividing and selling parcels to individuals 管制资源的使用 征收矫正性税收，使外部性内在化 例如：打猎与捕鱼的许可证，对拥挤的国家公园收门票 拍卖使用资源的许可证 例如：美国联邦通信委员会的频谱拍卖 如果资源是土地，将土地分为小块，并出售给个人，使之成为私人物品 The electromagnetic frequency spectrum is a common resource. It is not excludable: anyone with the right equipment can use it. It is rival in consumption: there’s a limited amount of spectrum available. The U.S. FCC has been auctioning licenses to use parts of the spectrum since These auctions raise substantial revenue for the federal government, and help allocate spectrum efficiently (firms that can use it most productively bid the most in the auctions). 16

17 Some Important Common Resources
Clean air and water Congested roads Fish, whales, and other wildlife 清洁的空气和水 拥挤的道路 鱼，鲸和其他野生物 Regarding congested roads: please encourage your students to read the new “In the News” box entitled “A Solution to City Congestion.” 17

18 CASE STUDY: “You’ve Got Spam!” “你有一封垃圾邮件!”
Some firms use spam s to advertise their products. Spam is not excludable: Firms cannot be prevented from spamming. Spam is rival: As more companies use spam, it becomes less effective. Thus, spam is a common resource. Like most common resources, spam is overused – which is why we get so much of it! 一些企业使用垃圾邮件来 推广它们的产品 垃圾邮件没有排他性： 企业不能阻止垃圾邮件 垃圾邮件有竞争性：随着更多 的公司使用垃圾邮件来推广产品，它会变得越来越没有效果 因此，垃圾邮件是一种公有资源 像大部分公有资源一样，垃圾邮件被过度使用—这就是为什么我们经常收到它的原因！ This case study is not in the textbook. 18

19 CONCLUSION 公共物品往往供给不足，而公共资源却过度消费 这些问题的产生源于产权没有很好的建立：
Public goods tend to be under-provided, while common resources tend to be over-consumed. These problems arise because property rights are not well-established: Nobody owns the air, so no one can charge polluters. Result: too much pollution. Nobody can charge people who benefit from national defense. Result: too little defense. The govt can potentially solve these problems with appropriate policies. 公共物品往往供给不足，而公共资源却过度消费 这些问题的产生源于产权没有很好的建立： 没有人拥有空气的产权，因此没人能对污染者收费。结果：太多的污染 没人能对从国防中获益的人收费。结果：太少的防卫 政府能够用合适的政策潜在的解决这些问题 19

20 CHAPTER SUMMARY A good is excludable if someone can be prevented from using it. A good is rival in consumption if one person’s use reduces others’ ability to use the same unit of the good. Markets work best for private goods, which are excludable and rival in consumption. Markets do not work well for other types of goods. 一种物品具有排他性是说阻止一些人使用该物品是可能的。如果一个人对某种物品的使用减少了其他人对同一物品的使用，这种物品就具有竞争性 市场运行最适用于既有排他性又有竞争性的私人物品。市场运行不适用于其他类型的物品 20

21 CHAPTER SUMMARY 公共物品，比如国防和基础知识，既不具有排他性，也不具有消费中的竞争性
Public goods, such as national defense and fundamental knowledge, are neither excludable nor rival in consumption. Because people do not have to pay to use them, they have an incentive to free ride, and firms have no incentive to provide them. Therefore, the government provides public goods, using cost-benefit analysis to determine how much to provide. 公共物品，比如国防和基础知识，既不具有排他性，也不具有消费中的竞争性 由于人们无需对这些物品的使用付费，因此他们有搭便车的激励，企业则没有提供这些物品的激励 因此，政府提供公共物品，并以成本-收益分析为基础做出关于每种物品供给量的决策 21

22 CHAPTER SUMMARY 公共资源在消费中有竞争性但无排他性。例子包括公有的草地清洁的空气和拥挤的道路
Common resources are rival in consumption but not excludable. Examples include common grazing land, clean air, and congested roads. People can use common resources without paying, so they tend to overuse them. Therefore, governments try to limit the use of common resources. 公共资源在消费中有竞争性但无排他性。例子包括公有的草地清洁的空气和拥挤的道路 由于不能向使用公共资源的人收费，他们往往会过度地使用公共资源。因此，政府努力用各种方法限制公共资源的使用 22