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chapter:

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Krugman/Wells

©2009 Worth Publishers

Economic Models: Trade-offs and Trade

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WHAT YOU WILL LEARN IN THIS CHAPTER

Why models? Simplified representations of reality—play a crucial role in economics

Two simple but important models:

production possibility frontier

circular-flow diagram

The difference between positive economics and normative economics

When economists agree and why they sometimes disagree

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Models in Economics

A model is a simplified representation of a real situation that is used to better understand real-life situations.

Create a real but simplified economy Ex.: Cigarettes in World War II prison camps Simulate an economy on a computer Ex.: Tax models, money models…

The “other things equal” assumption means that all other relevant factors remain unchanged.

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Trade-offs: The Production Possibility Frontier

The production possibility frontier (PPF) illustrates the trade-offs facing an economy that produces only two goods. It shows the maximum quantity of one good that can be produced for any given production of the other.

The PPF improves our understanding of trade-offs by considering a simplified economy that produces only two goods by showing this trade-off graphically.

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The Production Possibility Frontier

2820 400

30

9

15

Quantity of coconuts

Production possibility frontier

A

B

D

C

Feasible and efficientin production

Not feasible

PPF

Quantity of fish

Feasible butnot efficient

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Increasing Opportunity Cost

A

PPF

10 20 30 40 500

35

30

25

20

15

10

5

Producing the first 20 fish . . .

…requires giving up 25 more coconuts…

…requires giving up 5 coconuts

But producing 20 more fish . . .

Quantity of coconuts

Quantity of fish

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Economic Growth

Economic growth results in an outward shift of the PPF because production possibilities are expanded.

The economy can now produce more of everything.

Production is initially at point A (20 fish and 25 coconuts), it can move to point E (25 fish and 30 coconuts).

A

10 20 25 30 40 500

35

30

25

20

15

10

5

E

NewPPF

Original

PPF

Quantity of coconuts

Quantity of fish

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Production Possibilities for Two Castaways

28 400

30

9

(a) Tom’s Production Possibilities

Tom’s consumptionwithout trade

Tom’sPPF

Quantity of coconuts

Quantity of fish

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Production Possibilities for Two Castaways

1060

20

8

Hank’s

PPF

Quantity of coconuts

Quantity of fish

(a) Hank’s Production Possibilities

Hank’s consumptionwithout trade

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Tom and Hank’s Opportunity Costs

Tom’s Opportunity Cost

Hank’s Opportunity Cost

One fish 3/4 coconut 2 coconuts

One coconut

4/3 fish 1/2 fish

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Specialize and Trade

Both castaways are better off when they each specialize in what they are good at and trade.

It’s a good idea for Tom to catch the fish for both of them, because his opportunity cost of a fish in terms of coconuts not gathered is only 3/4 of a coconut, versus 2 coconuts for Hank.

Correspondingly, it’s a good idea for Hank to gather coconuts for the both of them.

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Comparative Advantage and Gains from Trade

28 400

30

910

1060

20

810

(a) Tom’s Production and Consumption

Tom’s consumption without trade

30

Tom'sPPF

Hank'sPPF

Quantity of coconuts Quantity of coconuts

Quantity of fishQuantity of fish

Tom’s consumption with trade

Tom’s production with trade

(b) Hank’s Production and Consumption

Hank’s production with trade

Hank’s consumption with trade

Hank’s consumption without trade

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How the Castaways Gain from Trade

Both Tom and Hank experience gains from trade:

Tom’s consumption of fish increases by two, and his consumption of coconuts increases by one.

Hank’s consumption of fish increases by four, and his consumption of coconuts increases by two.

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Comparative vs. Absolute Advantage

An individual has a comparative advantage in producing a good or service if the opportunity cost of producing the good is lower for that individual than for other people.

An individual has an absolute advantage in an activity if he or she can do it better than other people. Having an absolute advantage is not the same thing as having a comparative advantage.

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Tom vs. Hank – Absolute vs. Comparative

Tom has an absolute advantage in both activities: he can produce more output with a given amount of input (in this case, his time) than Hank.

But we’ve just seen that Tom can indeed benefit from a deal with Hank because comparative, not absolute, advantage is the basis for mutual gain.

So Hank, despite his absolute disadvantage, even in coconuts, has a comparative advantage in coconut gathering.

Meanwhile Tom, who can use his time better by catching fish, has a comparative disadvantage in coconut-gathering.

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Comparative Advantage and International Trade

0

1,500

1,000

Quantity of pork (millions of tons)

Quantity of aircraft

(a) The U.S. Production Possibilities Frontier

321 0

3,000

2,000

1,500

10.5 1.5

U.S.PPF

CanadianPPF

Quantity of pork (millions of tons)

Quantity of aircraft

(b) Canadian Production Possibilities Frontier

U.S. consumption without trade U.S.

consumption with trade

U.S. production with trade

Canadian production with trade

Canadian consumption with trade

Canadian consumption without trade

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Comparative Advantage and International Trade

Just like the example of Tom and Hank, the U.S. and Canada can both achieve mutual gains from trade.

If the U.S. concentrates on producing pork and ships some of its output to Canada, while Canada concentrates on aircraft and ships some of its output to the U.S., both countries can consume more than if they insisted on being self-sufficient.

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PITFALLS

Misunderstanding Comparative Advantage

A common mistake is to confuse comparative advantage with absolute advantage.

Ex.: U.S. vs. Japan in 1980s:

Commentators: “U.S. might soon have no comparative advantage in anything”

Wrong! They meant “absolute advantage”

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Trade takes the form of barter when people directly exchange goods or services they have for goods or services they want.

The circular-flow diagram is a model that represents the transactions in an economy by flows around a circle.

Transactions: The Circular-Flow Diagram

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The Circular-Flow Diagram

Money

FactorsGoods

andservices

Factors

Households

Firms

Markets for goods and services

Factor Markets

Goodsand

services

Money Money

Money

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Circular-Flow of Economic Activities

A household is a person or a group of people that share their income.

A firm is an organization that produces goods and services for sale.

Firms sell goods and services that they produce to households in markets for goods and services.

Firms buy the resources they need to produce—factors of production—in factor markets.

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Circular-Flow of Economic Activities

Ultimately, factor markets determine the economy’s income distribution, how total income is divided among the owners of the various factors of production.

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Using Models

Positive economics is the branch of economic analysis that describes the way the economy actually works.

Normative economics makes prescriptions about the way the economy should work.

A forecast is a simple prediction of the future.

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Using Models

Economists can determine correct answers for positive questions, but typically not for normative questions, which involve value judgments.

The exceptions are when policies designed to achieve a certain prescription can be clearly ranked in terms of efficiency.

It is important to understand that economists don’t use complex models to show “how clever they are,” but rather because they are “not clever enough” to analyze the real world as it is.

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When and Why Economists Disagree

There are two main reasons economists disagree:

Which simplifications to make in a model

Values

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SUMMARY

1. Almost all economics is based on models. An important assumption in economic models is the other things equal assumption, which allows analysis of the effect of a change in one factor by holding all other relevant factors unchanged.

2. One important economic model is the production possibility frontier. It illustrates: opportunity cost, efficiency, and economic growth. There are two basic sources of growth: an increase in factors of production, resources such as land, labor, capital, and human capital, inputs that are not used up in production, and improved technology.

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SUMMARY

3. Another important model is comparative advantage, which explains the source of gains from trade between individuals and countries. Everyone has a comparative advantage in something. This is often confused with absolute advantage, an ability to produce a particular good or service better than anyone else.

4. In the simplest economies, people barter or trade goods and services for one another—rather than trade them for money, as in a modern economy. The circular-flow diagram represents transactions within the economy as flows of goods, services, and money between households and firms. These transactions occur in markets for goods and services and factor markets.

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SUMMARY

5. Economists use economic models both for positive economics, which describes how the economy works, and for normative economics, which prescribes how the economy should work. Positive economics often involves making forecasts. Economists can determine correct answers for positive questions, but typically not for normative questions, which involve value judgments.

6. There are two main reasons economists disagree. One, they may disagree about which simplifications to make in a model. Two, economists may disagree—like everyone else—about values.

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The End of Chapter 2

Coming attractionChapter 3:

Supply and Demand