1. Public Goods and Common Resources11
Public Goods and Common Resources
Microeconomics
P R I N C I P L E S O F
N. Gregory Mankiw
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.
Premium PowerPoint Slides by Ron Cronovich

2. 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? 1

3. Introduction
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.
PUBLIC GOODS AND COMMON RESOURCES 2

4. 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
PUBLIC GOODS AND COMMON RESOURCES 3

5. 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
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.
PUBLIC GOODS AND COMMON RESOURCES 4

6. A C T I V E L E A R N I N G 1 Categorizing roads
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.
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

7. A C T I V E L E A R N I N G 1 Answers
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

8. The Different Kinds of Goods
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.
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9. Public Goods
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.
PUBLIC GOODS AND COMMON RESOURCES 8

10. Public Goods
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.
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11. Some Important Public Goods
National defense
Knowledge created through basic research
Fighting poverty
PUBLIC GOODS AND COMMON RESOURCES 10

12. Common Resources
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
PUBLIC GOODS AND COMMON RESOURCES 11

13. The Tragedy of the Commons
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.
PUBLIC GOODS AND COMMON RESOURCES 12

14. 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.
PUBLIC GOODS AND COMMON RESOURCES 13

15. A C T I V E L E A R N I N G 2 Policy options for common resources
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

16. A C T I V E L E A R N I N G 2 Answers
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

17. Policy Options to Prevent Overconsumption of Common Resources
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
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).
PUBLIC GOODS AND COMMON RESOURCES 16

18. Some Important Common Resources
Clean air and water
Congested roads
Fish, whales, and other wildlife
Regarding congested roads: please encourage your students to read the new “In the News” box entitled “A Solution to City Congestion.”
PUBLIC GOODS AND COMMON RESOURCES 17

19. CASE STUDY: “You’ve Got Spam!”
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!
“Spam” is named after everyone’s favorite delicacy.
This case study is not in the textbook.
PUBLIC GOODS AND COMMON RESOURCES 18

20. CONCLUSION
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.
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21. 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. 20

22. CHAPTER SUMMARY
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. 21

23. CHAPTER SUMMARY
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. 22