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Chapter 03

Why Everybody Trades: Comparative Advantage

Overview

This chapter extends the analysis of international trade to consider trade in a multiple-product economy. An economy composed of two products is useful to bring out insights about international trade. This general equilibrium approach explicitly shows the effects of resource reallocations between industries. The chapter culminates in showing the importance of comparative advantage for understanding why countries trade.

The story begins with Adam Smith and absolute advantage. (A box on mercantilism summarizes the view that Smith opposed and shows how mercantilist thinking continues today.) The analysis focuses on the productivity of labor (output per hour) in producing each of two products (wheat and cloth) in two countries (the United States and the rest of the world). Smith examined the case of absolute advantage, in which labor productivity in producing one product is higher in one country and labor productivity in producing the other product is higher in the other country. With no trade each country must produce both products to meet national demands. The discussion of the Smith case focuses on the increase in global production efficiency achieved by shifting production in each country toward the product in which it has the higher labor productivity. National demands can be met by international trade—apparently excess supplies can be exported and apparently excess demands can be met by imports. The increase in total world production is the evidence of gains from international trade.

Smith's approach does not indicate what would happen if the same country has absolute advantage in both products. Ricardo took up this case and demonstrated the principle of comparative advantage—a country will export products that it can produce at low opportunity cost and import products that it would otherwise produce at high opportunity cost. The Ricardian example is developed in more detail. The ratio of resource costs (or labor hour input-output coefficients, the inverse of labor productivities) indicates the opportunity costs or relative prices of the products in each country with no trade. The difference in prices with no trade sets up the opportunity for arbitrage, with each good being exported from the initially low-price country and imported by the initially high-price country. The shift to a free trade equilibrium results in an equilibrium international price. Without information on demand, we cannot say exactly what this price will be, but we do know that it is in the range bordered by the two no-trade price ratios.