Comparative Advantage

Comparative advantage is the ability of a country, firm or person to produce a good or service at a lower opportunity cost than someone else, meaning it gives up less of other goods to make it. The principle shows that two parties can both gain from trade even when one of them is more efficient at producing everything, provided each concentrates on what it gives up least to make. It is the core idea of international trade theory.

The principle is usually credited to David Ricardo's On the Principles of Political Economy and Taxation (1817), with Robert Torrens stating a version two years earlier. It refined Adam Smith's absolute advantage, which compares raw efficiency, and it remains the standard economic argument for free trade. It sits within classical economics but has been extended by every later school of trade theory.

Think of a senior lawyer who also types faster than her assistant. She could do her own typing, but every hour spent typing is an hour not spent advising clients, which is worth far more. The assistant types a little slower, yet giving up nothing as valuable to do it. Both end up better off if she sticks to legal work and he does the typing, even though she is better at both tasks. Her decision is a classic trade-off: because her hours are limited, every extra hour of typing means an hour less of far more valuable legal work.

Countries work the same way. A country may be better at making cars and growing wheat than its neighbor, but if it is far better at cars and only slightly better at wheat, it should make cars and buy wheat. What matters is not who is best, but who sacrifices least.

The opportunity cost of good X in terms of good Y is the amount of Y given up to make one more unit of X. With labor as the only input:

• $a_{X}$ is the labor hours needed to make one unit of X.
• $a_{Y}$ is the labor hours needed to make one unit of Y.
• $\text{OC}_{X}$ is the units of Y forgone per unit of X.

Suppose country A needs 2 hours for a shirt and 4 hours for a tonne of wheat, while country B needs 6 hours for a shirt and 8 hours for a tonne of wheat. A is more efficient at both. A shirt costs A $2 \div 4 = 0.5$ tonnes of wheat, but costs B $6 \div 8 = 0.75$ tonnes. A tonne of wheat costs A $4 \div 2 = 2$ shirts, but costs B only $8 \div 6 \approx 1.33$ shirts. So A has the comparative advantage in shirts and B in wheat. At any trade price between 0.5 and 0.75 tonnes of wheat per shirt, both gain.

Ricardo's own example used England and Portugal, with Portugal more efficient at both wine and cloth but relatively more so at wine. The real-world counterpart of the trade price is the terms of trade.

• Technology differences. The Ricardian model puts trade down to different productivity across industries.
• Factor endowments. The Heckscher–Ohlin model, developed by Eli Heckscher and Bertil Ohlin, says countries export goods that use their abundant factors of production intensively: labor-rich countries export labor-intensive goods, capital-rich countries capital-intensive ones. Ohlin shared the 1977 Nobel prize in economics.
• Scale and variety. Paul Krugman's work on trade with economies of scale, recognized with the 2008 Nobel prize, explains why similar rich countries trade similar goods with each other.
• Acquired skills. Learning, clusters and industrial policy can create advantages over time, as the infant industry argument holds.

Opportunity costs before trade cannot be observed directly, so researchers look at trade data instead. The common measure is Bela Balassa's revealed comparative advantage (RCA) index from 1965:

Here $x_{ij}$ is country i's exports of product j, $X_{i}$ its total exports, and the $w$ terms are the same for the world. A value above 1 suggests a comparative advantage. If textiles make up 50% of a country's exports but 5% of world exports, its RCA is $0.50 \div 0.05 = 10$, a strong revealed advantage, as seen in the export profiles of Pakistan and Bangladesh.

Paul Samuelson, the 1970 Nobel laureate, called comparative advantage one of the few ideas in social science that is both true and not obvious. Even supporters note its limits. The gains are national totals, so workers and firms in import-competing industries can lose, and research on the rise of Chinese imports into the United States after 2001 found lasting job and wage losses in exposed regions. The model assumes full employment and easy movement of workers between industries, which real labor markets lack. Critics in the protectionist and developmentalist traditions argue that static comparative advantage can lock poorer countries into raw materials, and that developing countries should build new advantages deliberately. Others point out that mobile capital and multinational supply chains blur the idea of a national advantage. Most economists still accept the principle while debating how to share the gains, for example through welfare and retraining.

• David Ricardo, On the Principles of Political Economy and Taxation (Project Gutenberg)
• The Nobel Prize in Economic Sciences 2008