What is comparative advantage? Why trade helps both sides

Comparative advantage is the ability to produce something at a lower opportunity cost than someone else: giving up less of other things to make it. It explains why two people or two countries can both gain from trade even when one is better at making everything. Each should do more of what it gives up least to make, and trade for the rest. The idea is David Ricardo's, from 1817, and it is the core of the economics of trade.

In short

• Absolute advantage is making more with the same resources; comparative advantage is giving up less to make something. Only comparative advantage decides who should make what.
• In Ricardo's example, Portugal is better at both wine and cloth, yet both Portugal and England end up with more by specializing and trading.
• Trade raises a country's total income, but some workers and places lose, and the losses can be large and lasting.

What is the difference between absolute and comparative advantage?

Absolute advantage is about productivity: who can make more of something with the same resources. Comparative advantage is about opportunity cost: who gives up less of something else to make it. A country, a firm or a person can have an absolute advantage in everything, but it can't have a comparative advantage in everything, because a low opportunity cost in one good means a high one in the other.

A familiar picture: a lawyer who types faster than her assistant still hires the assistant to type. Every hour she spends typing is an hour of legal work not billed, so typing costs her far more in what she gives up than it costs him. She has the absolute advantage in typing, and he has the comparative advantage. The short example in the overview of economics shows the same logic with two people baking and knitting; Ricardo's version, below, is the one economists still teach.

How does Ricardo's wine and cloth example work?

In chapter 7 of On the Principles of Political Economy and Taxation, published in 1817, Ricardo imagined two countries and two goods, and stated how many workers it took for a year to make one unit of each:

	Cloth	Wine
England	100 workers	120 workers
Portugal	90 workers	80 workers

Portugal needs fewer workers for both, so it has the absolute advantage in both. Here is why trade still pays, step by step.

Step 1: the opportunity costs. In England, the 120 workers who make one unit of wine could instead make 1.2 units of cloth (120 ÷ 100). So one wine costs England 1.2 cloth. In Portugal, the 80 workers who make one wine could make 0.89 units of cloth (80 ÷ 90). So one wine costs Portugal only 0.89 cloth. Wine is cheaper for Portugal in what it gives up, and cloth, by the same reasoning, is cheaper for England: one cloth costs England 0.83 wine and Portugal 1.125 wine.

Step 2: without trade. Each country makes one unit of each good. England uses 220 workers, Portugal 170. The world has 2 cloth and 2 wine.

Step 3: with specialization. England puts all 220 workers into cloth and makes 2.2 units. Portugal puts all 170 into wine and makes 2.125 units. With the same workers, the world now has 2.2 cloth and 2.125 wine, more of both goods than before, from nothing but each country doing what costs it least to give up.

Step 4: trade. Suppose they swap one cloth for one wine. England keeps 1.2 cloth and gets 1 wine, so it ends with 0.2 more cloth than before. Portugal keeps 1.125 wine and gets 1 cloth, so it ends with 0.125 more wine. Both are better off. Any rate of exchange between England's 1.2 cloth per wine and Portugal's 0.89 cloth per wine leaves both ahead; where in that range the price lands decides how the gain is shared. OpenStax works the same result with modern numbers in its chapter on a country with an absolute advantage in all goods.

Why does comparative advantage matter?

It overturns the intuition that trade is a contest a less productive country must lose. A poorer country with lower productivity in everything still has goods where its disadvantage is smallest, and it gains by specializing in those. A rich country gains by buying them rather than moving its own workers out of the industries where they are most productive. The gain comes from the difference in opportunity costs, not from either side being cheap or skilled.

The same reasoning works inside a country, between regions, firms and households, and it is one reason specialization and the division of labor run through market economies. It also explains why rules on trade sit at the center of institutions such as the World Trade Organization and the IMF, and why most economists are wary of a tariff as a way to make a country richer overall.

What does the simple model leave out?

Ricardo's example has two goods, two countries, labor as the only input, no transport costs, and workers who can move instantly from cloth to wine. Each simplification hides a real cost:

The model assumes	In practice
Workers switch industries freely	Skills, homes and pensions tie people to jobs and places
Everyone stays employed	Job losses from imports can last years in the places hit
Gains and losses are spread evenly	Gains are spread across all buyers; losses fall on particular workers and towns
Countries are fixed in what they're good at	Comparative advantage shifts as countries invest, learn and grow
Trade is the only change	Exchange rates, technology and policy move at the same time

The best-known evidence on the second and third rows is the "China shock." David Autor, David Dorn and Gordon Hanson studied US local labor markets as imports from China rose after 1990. They found that rising import exposure raised unemployment, lowered labor force participation and reduced wages in the places most affected, and that, conservatively, it explained one quarter of the decline in US manufacturing employment over the period they studied. Government payments for unemployment, disability and health care rose sharply in those areas too.

Still argued

Economists broadly agree that trade based on comparative advantage raises a country's total income, and that it creates losers as well as winners. They argue over how big the losses are and what to do about them. One view, held by many trade economists, is that the gains are large and widely spread through lower prices, and that losses are best met with retraining, wage insurance and support for affected places, such as the US Trade Adjustment Assistance program created in 1962, rather than with barriers to trade. Another view, sharpened by the China-shock research, is that adjustment costs were underestimated, that help for displaced workers has been too small to make up for them, and that the pace and terms of opening to trade matter, not just the direction. Some economists, such as Ha-Joon Chang, argue that today's rich countries protected their industries while developing, and that comparative advantage at a given moment shouldn't lock a poor country into what it makes now. This note sets out the arguments; it takes no position on any current trade policy.

What does comparative advantage lead to?

Comparative advantage is the payoff of thinking in opportunity costs, and it builds on scarcity: because no one can make everything, the question is always what each side gives up. Later trade theory added differences in land, capital and skills, economies of scale, and trade between similar countries in similar goods, such as cars traded both ways between Germany and Japan. But the basic result has held since 1817: two sides with different opportunity costs can both gain from specializing and trading.

Check yourself

• In Ricardo's example, Portugal is better at making both goods. Why does it still gain by trading with England?
• What is the opportunity cost of one unit of wine in England and in Portugal, and how do you work it out?
• Why can trade raise a country's total income and still leave some of its workers worse off?

Sources

• On the Principles of Political Economy and Taxation — David Ricardo, 1817, Library of Economics and Liberty
• 33.2 What Happens When a Country Has an Absolute Advantage in All Goods — OpenStax, Principles of Economics 3e, 2022
• The China Syndrome: Local Labor Market Effects of Import Competition in the United States — Autor, Dorn and Hanson, NBER, 2012
• Comparative advantage — Wikipedia