What you will learn in this chapter:
1. Why models play a crucial role in economics?
2. Production possibility frontier (PPF)
3. Comparative advantage
4. Circular-flow diagram
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1. Models in Economics
A model is a simplified representation of a real situation that is used to better understand real-life situations.
 Ex: concept of equilibrium – example of how customers at a supermarket would rearrange themselves when a new cash register opens
The “other things equal” assumption means that all other relevant factors remain unchanged.
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2. Trade-offs: The Production Possibility
Frontier
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Increasing Opportunity Cost
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Economic Growth
The economy can now
A outward shift of the PPF because production E possibilities are expanded.
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3. Comparative Advantage and Gains from
Trade. Ex.: Tom and Hank
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3. Comparative Advantage and Gains from
Trade. Ex.: Tom and Hank
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Tom and Hank’s Opportunity Costs of
Fish and Coconuts
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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Comparative Advantage and Gains from Trade.
Ex.: Tom and Hank
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Comparative Advantage and Gains from Trade
Ex.: Tom and Hank
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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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3. 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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4. Transactions: The Circular-Flow
Diagram
Trade takes the form of barter (Tom & Hank example above) when people directly exchange goods or services that they have for goods or services that they want.
The circular-flow diagram is a model that represents the transactions in an economy by flows around a circle.
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The Circular-Flow Diagram
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Growth in the U.S. Economy from 1962…
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…to 1988
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Summary
1. Almost all economics are based on models,
“thought experiments” or simplified versions of reality. Important assumption: other things equal
2. Production possibility frontier: illustrates opportunity cost, efficiency, and economic growth
3. Comparative advantage: explains source of gains from trade. Often confused with absolute advantage
4. Circular-flow diagram: represents transactions occur in markets for goods and services & factor markets
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