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Microeconomics Topic 2: “Explain the principle of comparative advantage and how it leads to specialization and gains from trade.”
Reference: Gregory Mankiw’s Principles of Microeconomics , 2nd^ edition, Chapter 3.
Why People and Countries Trade
This section lays the foundation for why countries and individuals gain from trade. Countries usually trade to buy goods that are produced at a lower cost elsewhere. Countries and people have different costs of production or (to put it differently) different abilities in producing goods. They can take advantage of their differences in order to make themselves better off. When they do this, they experience gains from trade.
The following concepts are important in understanding gains from trade:
- Opportunity cost: a cost that is measured in terms of what you give up of some other good. Time spent producing cars is time taken away from producing bread, and vice versa. Note that when we discuss gains from trade, the opportunity cost is not measured in dollars but in units of some good or activity that is given up. For a review of opportunity cost, see the notes for Micro Topic 1.
- Absolute advantage: The person or country that produces a good with a smaller quantity of inputs, or that produces more output per unit of input, is said to have an absolute advantage in producing that good.
- Comparative advantage: The person or country that has the smaller opportunity cost of producing a good is said to have a comparative advantage in producing that good. Comparative advantage determines which country will specialize in which good.
The gains from trade are only based on comparative advantage , not on absolute advantage. A country or person can have an absolute advantage in both goods or activities, and yet still gain from trade by specializing in the good or activity in which it has a comparative advantage.
We will go over an example very carefully, step by step, to highlight all the important concepts associated with the topic of “gains from trade and comparative advantage.”
Calculating Absolute and Comparative Advantage
Martha and Sheldon wallpaper and paint rooms. In one week, Martha can paint 20 rooms or wallpaper 5 rooms. In the same amount of time, Sheldon can paint 10 rooms or wallpaper 4 rooms. The information is usually summarized in a table like this one:
Table 1: Production Possibilities for 1 Week Rooms Finished in 1 Week
Paint Wallpaper Martha 20 5 Sheldon 10 4
If they want, Martha and Sheldon can also split their time between activities. For example, Martha could spend 50% of her week on painting and 50% of her week on wallpapering, to produce 10 painted rooms and 2.5 wallpapered rooms.
Using the information here, we can determine absolute advantage. Since Martha can produce more painted rooms than Sheldon in the same amount of time (20 > 10), she has the absolute advantage in painting. Since she can produce more wallpapered rooms than Sheldon in the same amount of time (5 > 4), she also has the absolute advantage in wallpapering.
The goal of this exercise is to show you that Martha and Sheldon are better off if they specialize in the good in which they have a comparative advantage and then trade, rather than trying to produce everything for themselves and not trading. This is true even though Martha has the absolute advantage in both activities.
Let’s start with the case of no trade, and assume that each person spends half a week on each activity. The resulting output is given in Table 2.
Table 2: Production without Specialization Martha Sheldon Rooms Painted Rooms Wallpapered Rooms Painted Rooms Wallpapered 10 2.5 5 2
For future reference, notice that the total production is 15 (10 + 5) rooms painted and 4. (2.5 + 2) rooms wallpapered.
Remember that the person who has the smaller opportunity cost is said to have a comparative advantage. Therefore, we need to calculate the opportunity cost of each activity for each person. This is a very crucial step, so make sure you understand how it is done!
Let us start with the opportunity cost of painting. By looking at Table 1, we can see that when Martha paints 20 rooms, she gives up wallpapering 5 rooms. Divide both numbers by 20 and we find that when Martha paints 1 room, she gives up wallpapering 5/20 or 0.25 rooms. So for Martha, the opportunity cost of 1 painted room is 0.25 wallpapered rooms.
Now we repeat the process for Sheldon. For him, painting 10 rooms means not wallpapering 4 rooms. Dividing both numbers by 10, we find that when Sheldon paints 1 room, he gives up wallpapering 0.4 rooms. So for Sheldon, the opportunity cost of 1 painted room is 0.4 wallpapered rooms.
4.5), but more rooms painted now (14 + 2.5 = 16.5). We have increased the number of rooms painted by 1.5 without lowering the number of rooms wallpapered! This is the gain from specialization.
But even if the total production is higher, does that mean both Martha and Sheldon are better off specializing? The answer is yes, if they engage in trade.
In the real world, trade is accomplished by selling goods at market prices. But since we don’t have dollar prices in this example, we need to figure out the exchange price of painting in terms of wallpapering and the exchange price of wallpapering in terms of painting. Logic tells us that the seller of the activity will never voluntarily sell for a price below her opportunity cost, as she would lose money. Similarly, the buyer of an activity will never voluntarily pay a price higher than her opportunity cost, as she could just produce the activity herself at lower cost.
In our case, the “price” of, say, wallpapering will be between the range of 2.5 rooms painted (opportunity cost of the seller, Sheldon) and 4 rooms painted (opportunity cost of the buyer, Martha). The exact exchange price will depend on the bargaining powers of the traders. Let’s assume that Sheldon and Martha will exchange 1 room wallpapered for 3 rooms painted.
Note: the exchange price (the price of good X in terms of good Y) must lie somewhere between the opportunity costs (of good X in terms of good Y) of the two traders. You will always be given the exact exchange price because it cannot be determined from the information given here.
Think of the exchange price in this way: Martha will go to Sheldon’s house and paint 3 rooms, while Sheldon will go to Martha’s house and wallpaper 1 room. That’s the trade. The resulting exchange will provide the following outputs in one week:
Table 5: Consumption with Specialization and Trade Martha Sheldon Rooms Painted Rooms Wallpapered Rooms Painted Rooms Wallpapered 14 – 3 = 11 1.5 + 1 = 2.5 2.5 + 3 = 5.5 3 – 1 = 2
Notice that Martha is better off with specialization and trade than she was without trade (in Table 2), because she has just as many wallpapered rooms (2.5) but one more painted room (11). Sheldon is also better off with specialization and trade, because he has just as many wallpapered rooms (2) but one-half more painted rooms (5.5). So Martha and Sheldon both gain from trade.
Major insights: Martha’s absolute advantage in wallpapering and painting means that she is better at both activities than Sheldon is. Yet, even though Sheldon is worse at painting and wallpapering, he has a comparative advantage in wallpapering -- the activity in which he is the least inefficient. Thus, Martha can gain by having Sheldon wallpaper 1 of her rooms even though she could have wallpapered the room faster than Sheldon did. This
exchange allowed Martha to specialize in painting -- the activity in which she is even more efficient.
We have focused on trade between individuals, but our insights apply to trade between nations as well. The gains from trade are obvious when one country is better at producing one good and its trading partner is better at producing another. It is less obvious, but also true, that if one country is better at producing everything, then both countries can still gain from trade.
