4.1 Benefits of international trade | IB DP Economics

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Why do countries trade, and who gains? This page covers the benefits of international trade, the two free-trade diagrams (world price below and above the domestic price) that underpin every protection diagram in 4.2, and at HL the theory of absolute and comparative advantage: the surprising result that a country gains from trade even if it is worse at producing everything.

🎯What you need to be able to do

Explain the benefits of international trade: competition, lower prices, greater choice, access to resources, foreign exchange, larger markets, economies of scale, and more efficient resource allocation and production.
Draw free-trade diagrams showing exports when the world price is above the domestic price, and imports when it is below.
HL Calculate from a diagram the quantity of exports and imports, import expenditure and export revenue.
HL Explain absolute and comparative advantage, opportunity costs, gains from trade and the sources of comparative advantage; draw linear PPCs showing gains from specialization; calculate opportunity costs to identify comparative advantage; evaluate the limitations of the theory.

📚The economics

Benefits of international trade

Increased competition: domestic firms face foreign rivals, so they must cut costs and innovate; monopoly power is reduced.
Lower prices for consumers, from cheaper imports and competitive pressure.
Greater choice: goods that cannot be made at home (Indonesian consumers buy wheat, which the tropics grow poorly; Europeans buy coffee and cocoa).
Acquisition of resources: countries lacking oil, minerals, technology or capital goods can obtain them.
More foreign exchange earnings from exports, which pay for imports of capital goods and help development.
Access to larger markets: firms can sell far beyond a small domestic market.
Economies of scale: producing for world markets lowers average costs.
More efficient resource allocation and production: countries specialize in what they do relatively best (comparative advantage), so world output rises.
Also: transfer of technology and ideas, and closer political ties.

Free trade diagrams

Start from a domestic market with domestic demand and supply. With free trade, a small country can buy or sell as much as it likes at the world price (P_w), which is set in world markets.

Left: the world price of 4 dollars is below the domestic equilibrium; domestic firms supply 50, consumers demand 80, and 30 are imported at a cost of 120 dollars. Right: the world price of 6 dollars is above the domestic equilibrium; firms supply 90, consumers buy 60, and 30 are exported earning 180 dollars. — Below the world price the country imports; above it the country exports.

World price below domestic equilibrium: imports
Domestic quantity supplied falls to Q_s; quantity demanded rises to Q_d; the gap Q_d − Q_s is imported. Consumers gain (lower price); domestic producers lose. HL Import expenditure = P_w × imports.

World price above domestic equilibrium: exports
Domestic producers expand to Q_s; domestic consumers buy only Q_d; the excess Q_s − Q_d is exported. Producers gain, domestic consumers pay more. HL Export revenue = P_w × exports.

In both cases total social surplus is greater than without trade: the gains to the winners exceed the losses to the losers.

Absolute and comparative advantage HL

Absolute advantage
a country can produce more of a good with the same resources than another country (or the same amount with fewer resources). Adam Smith’s argument for trade.

Comparative advantage
a country can produce a good at a lower opportunity cost than another country. David Ricardo (1817) showed that trade based on comparative advantage benefits both countries, even if one has an absolute advantage in everything.

Gains from trade: if each country specializes (fully or partly) in the good in which it has a comparative advantage and trades, total world output rises, and both countries can consume outside their own PPC. The terms of trade must lie between the two countries’ opportunity costs for both to gain.

Sources of comparative advantage: differences in factor endowments (land, climate, natural resources: Indonesia’s palm oil and nickel; labour abundance for labour-intensive goods); human capital and technology; infrastructure; institutions; and experience/economies of scale built over time (dynamic comparative advantage).

Limitations of the theory:

Assumptions: constant opportunity costs (straight-line PPCs), no transport costs, perfect mobility of factors within a country, perfect competition and information, no trade barriers. In reality costs rise with specialization, transport is costly, and resources are not easily moved from rice farming to electronics.
Structural unemployment in industries that lose out.
Overspecialization makes a country vulnerable to price swings or demand collapses (commodity dependence, 4.9).
Static: a country may lock itself into low-value primary production when it could develop new advantages.
Distribution: gains may be unevenly shared within and between countries.
Ignores externalities (the environmental cost of producing the export) and strategic goods (food and energy security).

✏️Worked example HL

Using all their resources, Country A can produce 120 tonnes of rice or 60 bales of cloth; Country B can produce 40 tonnes of rice or 40 bales of cloth. Before trade, each splits its resources evenly.
(a) Identify absolute and comparative advantage.
(b) Show that specialization and trade at 1 bale = 1.5 tonnes can benefit both.

(a) A has an absolute advantage in both goods (120 > 40, 60 > 40). Opportunity costs:

A: 1 rice costs 60 ÷ 120 = 0.5 cloth; 1 cloth costs 2 rice

B: 1 rice costs 40 ÷ 40 = 1 cloth; 1 cloth costs 1 rice

A has the lower opportunity cost of rice: comparative advantage in rice. B has the lower opportunity cost of cloth (1 < 2): comparative advantage in cloth.

(b) Before trade: A produces and consumes (30 cloth, 60 rice); B (20 cloth, 20 rice). Total: 50 cloth, 80 rice. After specialization: B produces only cloth (40), A produces 10 cloth and 100 rice. Total: 50 cloth, 100 rice: 20 tonnes more rice with the same cloth. A exports 30 rice for 20 cloth (1 cloth = 1.5 rice):

A consumes 30 cloth, 70 rice: +10 rice

B consumes 20 cloth, 30 rice: +10 rice

Two straight-line PPCs. Country A: from 120 rice to 60 cloth; before trade at 30 cloth and 60 rice, it produces 10 cloth and 100 rice and consumes 30 cloth and 70 rice, outside its PPC. Country B: from 40 rice to 40 cloth; before trade at 20 and 20, it produces 40 cloth and consumes 20 cloth and 30 rice, also outside its PPC. — After trade, both countries consume at points outside their own PPCs.

Check it. The terms of trade (1 cloth = 1.5 rice) lie between B’s cost of cloth (1 rice) and A’s (2 rice), so both gain. Consumption totals match production: rice 70 + 30 = 100, cloth 30 + 20 = 50.

Using absolute advantage to decide specialization. A is better at both, yet should still import cloth. Compare opportunity costs, and compute each one the same way (cost of 1 unit of the same good in both countries).

📝Practise

Tagged questions are modelled on a real IB question from that session, with our own wording, numbers and context.

1. [2 marks, Paper 2 style] Define the term comparative advantage.

The ability of a country to produce a good at a lower opportunity cost than another country.

2. HL [Paper 3 style] Domestic demand for wheat is 90 million tonnes and domestic supply 30 million tonnes at the world price of $250 per tonne. Calculate imports and import expenditure.

Imports = 90 − 30 = 60 million tonnes. Import expenditure = 60 m × $250 = $15 billion.

3. HL Country X can make 50 phones or 25 laptops; Country Y can make 30 phones or 10 laptops. Identify each country’s comparative advantage.

OC of 1 laptop: X = 50 ÷ 25 = 2 phones; Y = 30 ÷ 10 = 3 phones. X has the comparative advantage in laptops. OC of 1 phone: X = 0.5 laptop; Y = 0.33 laptop, so Y has the comparative advantage in phones (even though X has the absolute advantage in both).

4. [10 marks, Paper 1 (a) — modelled on November 2023 HL Paper 1 Q3(a)] Using a numerical example, explain why two countries can both gain from trade even if one is more productive in every good.

Define comparative advantage and opportunity cost. Numerical example or two linear PPCs; show each country specializing in its lower-opportunity-cost good; total output rises; trade at terms between the two opportunity costs lets both consume beyond their PPC. Explain why terms of trade must fall between the two costs, and note the assumptions.

5. [10 marks, Paper 1 (a) — modelled on May 2022 HL Paper 1 Q3(a)] Explain why a country that specializes according to its comparative advantage may still face economic problems.

Unrealistic assumptions (constant costs, no transport costs, factor mobility, no barriers); structural unemployment and adjustment costs; overspecialization and vulnerability to price shocks (diagram of volatile commodity prices); static view locking poor countries into primary production; unequal distribution of gains; strategic and environmental concerns. Explain each with an example.

6. [4 marks, Paper 2 style] Using a free-trade diagram, explain how cheaper world prices of soybeans affect domestic soybean farmers and tofu makers in Indonesia.

A fall in P_w (below the domestic equilibrium) reduces the price in Indonesia: domestic quantity supplied falls (farmers lose revenue and producer surplus; some leave the crop), quantity demanded rises, imports increase. Tofu and tempeh makers, who use soybeans as an input, gain from lower costs. Diagram: D, S, P_w1 and lower P_w2, Q_s falls, Q_d rises, imports widen.

🔗Go deeper — other people’s work

These are external resources, not mine. If one stops working, tell me and everything above it on this page still stands.

The Atlas of Economic Complexity (Harvard Growth Lab) — what each country exports and how that has changed.
WTO — World Trade Statistical Review.
Paul Krugman, Ricardo’s Difficult Idea — a short essay on why comparative advantage is so often misunderstood.