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Why do countries trade, and how does comparative advantage explain the gains from specialisation?

International trade and comparative advantage: absolute and comparative advantage, the gains from trade and specialisation, the terms of trade, and the limitations of the theory.

An Eduqas A520 answer to the theory of international trade, covering absolute and comparative advantage, how opportunity-cost differences generate gains from specialisation and trade, the terms of trade, and the assumptions and limitations of comparative advantage.

Generated by Claude Opus 4.813 min answerUpdated 2026-06-02

Reviewed by: AI editorial process; not yet individually human-reviewed

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Absolute advantage exists when a country can produce a good using fewer resources (more output per unit of input) than another. Comparative advantage exists when a country can produce a good at a lower opportunity cost than another. The law of comparative advantage says that total world output rises if each country specialises in the good in which it has the lower opportunity cost and then trades, even if one country has an absolute advantage in both goods. Trade lets countries consume beyond their production possibility frontier. The terms of trade (the ratio of export prices to import prices) determine how the gains are split: mutually beneficial trade occurs at an exchange ratio between the two countries' domestic opportunity-cost ratios. The theory rests on strong assumptions (no transport costs, perfect factor mobility, constant returns, no trade barriers) and has real-world limitations.

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What this dot point is asking
Absolute and comparative advantage
The gains from trade
The terms of trade
Limitations of the theory
Examples in context
Try this

What this dot point is asking

Eduqas wants you to distinguish absolute from comparative advantage, show how differences in opportunity cost generate gains from specialisation and trade, define the terms of trade, and recognise the assumptions and limitations of the theory. Comparative advantage is the foundation of the whole trade-and-development area of study and a key quantitative skill.

Absolute and comparative advantage

The crucial insight (due to David Ricardo) is that even a country with an absolute advantage in both goods still gains from trade, because it should concentrate its resources where its advantage is greatest (its comparative advantage) and import the other good.

The gains from trade

The terms of trade

Finding comparative advantage and a mutually beneficial trade

Step 1: state the data

Using one unit of resource, Country X can produce either 20 units of cloth or 10 units of wine; Country Y can produce either 12 units of cloth or 12 units of wine.

Step 2: calculate opportunity costs

In Country X, 1 wine costs $\frac{20}{10} = 2$ cloth, and 1 cloth costs $\frac{10}{20} = 0.5$ wine. In Country Y, 1 wine costs $\frac{12}{12} = 1$ cloth, and 1 cloth costs 1 wine.

Step 3: identify comparative advantage

Country X gives up less wine per cloth (0.5 versus 1), so it has the comparative advantage in cloth. Country Y gives up less cloth per wine (1 versus 2), so it has the comparative advantage in wine. Each should specialise accordingly.

Step 4: find a beneficial exchange ratio

Trade benefits both if the price of wine in terms of cloth lies between the two domestic ratios, that is between 1 (Country Y's cost) and 2 (Country X's cost) cloth per wine. At, say, 1.5 cloth per wine, Country X gets wine more cheaply than its own cost of 2, and Country Y gets more than its own cost of 1 cloth per wine. Both gain, and total output of cloth and wine rises after specialisation.

Limitations of the theory

The theory of comparative advantage rests on simplifying assumptions that limit its real-world application:

It ignores transport costs, which can wipe out a small comparative advantage.
It assumes perfect mobility of factors, but workers in a declining industry cannot instantly move, causing structural unemployment.
It assumes constant returns to scale and no externalities.
Specialisation can leave a country over-dependent on a few products; primary-commodity exporters face volatile prices and a possible long-run deterioration in the terms of trade.
It says nothing about the distribution of the gains within a country: some groups lose even if the country as a whole gains.

These limitations are the basis for evaluation and for the case some make for selective protection.

Examples in context

China and manufacturing. A comparative advantage in labour-intensive manufacturing reshaped world trade and consumption patterns.
Commodity exporters. Countries reliant on a single commodity (oil, copper, cocoa) illustrate the danger of over-specialisation and volatile terms of trade.
Services trade. The UK's comparative advantage in financial and professional services shapes its export profile and current account.

Try this

Q1. Explain the difference between absolute and comparative advantage. [4 marks]

Cue. Absolute = producing more from given resources (or using fewer); comparative = producing at a lower opportunity cost. Comparative advantage drives the gains from trade.

Q2. Explain one limitation of the theory of comparative advantage. [4 marks]

Cue. For example transport costs eroding a small advantage, factor immobility causing structural unemployment, or over-dependence on volatile primary commodities.

Exam-style practice questions

Practice questions written in the style of WJEC Eduqas exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.

Eduqas Component 2 20204 marksCountry A can produce 10 units of wheat or 5 cars with one unit of resource; Country B can produce 6 units of wheat or 6 cars. Identify which country has the comparative advantage in cars and explain how you reached your answer.

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A short calculate question. Comparative advantage lies with the country that has the lower opportunity cost.

In Country A, the opportunity cost of 1 car is $\frac{10}{5} = 2$ units of wheat. In Country B, the opportunity cost of 1 car is $\frac{6}{6} = 1$ unit of wheat.

Country B sacrifices less wheat per car (1 versus 2), so Country B has the comparative advantage in cars and should specialise in cars, leaving Country A to specialise in wheat. Markers reward the two opportunity-cost calculations and the correct identification based on the lower opportunity cost.

Eduqas Component 3 Section C 202112 marksEvaluate the view that free trade based on comparative advantage always benefits all countries involved.

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A levels-of-response essay. Knowledge and application: explain comparative advantage (specialise where opportunity cost is lowest) and the gains from trade (higher world output and consumption beyond each country's PPF). Use a numerical or PPF example.

Analysis: develop how specialisation and trade raise total output and allow consumption outside the production possibility frontier.

Evaluation: weigh the limitations and losers: the theory assumes no transport costs, perfect mobility and constant returns; specialisation can leave a country over-dependent on a few products (especially primary-commodity exporters with volatile prices); structural unemployment in declining industries; and the distribution of the gains depends on the terms of trade. Conclude with a supported judgement that trade raises total welfare but the gains are unevenly shared and some groups lose.

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Sources & how we know this

Eduqas A Level Economics Specification (A520) — Eduqas (2015)