Trade and the global economy

Q: Do I need to draw a comparative advantage PPF for 8-mark questions?

Yes, if the question asks to illustrate gains from trade, a fully labelled PPF or opportunity cost table with before/after specialisation figures will earn full KAA marks, provided you link it explicitly to your analysis.

Q: What weight is evaluation in Unit 4 extended answers?

Evaluation makes up 30% of marks for Unit 4 (IA2) papers: 6 marks for 14-mark questions, and 8 marks for 20-mark questions. Top evaluation includes magnitude, PED, time lags, and clear, justified judgements.

Edexcel International A-Level Economics· 4.3.2 (2018 spec)· 35 min read

1. Specialisation and Comparative Advantage★★☆☆☆⏱ 8 min

📘 Definition

Comparative Advantage

When a country can produce a good or service at a lower domestic opportunity cost than another country, even if it does not have an absolute advantage in producing any good.

Example:

Country A can produce 10 cars or 20 wheat units per worker; Country B can produce 4 cars or 16 wheat units per worker. Country B has comparative advantage in wheat, with an opportunity cost of 0.25 cars per unit of wheat vs 0.5 cars for Country A.

📐 Worked Example

Using the output data below, show the gains from specialisation between Country X and Y if they specialise in their comparative-advantage good and trade at a rate of 1 car = 2 textiles. Output per worker: Country X = 8 cars or 8 textiles; Country Y = 4 cars or 12 textiles.

1
Calculate opportunity costs: Country X: 1 car = 1 textile, 1 textile = 1 car; Country Y: 1 car = 3 textiles, 1 textile = 1/3 car.
2
Identify comparative advantage: Country X has the lower opportunity cost for cars (1 textile vs 3), Country Y the lower opportunity cost for textiles (1/3 car vs 1).
3
Pre-specialisation (each country splits its worker equally between the two goods): X = 4 cars + 4 textiles; Y = 2 cars + 6 textiles. Total global output = 6 cars + 10 textiles.
4
Post-specialisation: X produces 8 cars, Y produces 12 textiles. Total global output = 8 cars + 12 textiles — more of BOTH goods than before specialisation.
5
Trade 3 cars from X to Y for 6 textiles (rate 1 car = 2 textiles, which lies between the two opportunity costs). X ends with 5 cars + 6 textiles (+1 car, +2 textiles vs no trade); Y ends with 3 cars + 6 textiles (+1 car, same textiles). Both countries now consume beyond their own production possibilities, so both gain from trade.

Exam tip:

For 6-mark analyse questions on comparative advantage limitations, link each limitation directly to reduced welfare gains from trade to earn full KAA marks.

2. Patterns and Volume of World Trade★★☆☆☆⏱ 6 min

Global trade volumes have grown 10x since 1980, driven by structural economic shifts, changes in comparative advantage, and policy changes. Trade flows now favour manufactured goods and services over primary products, with emerging economies accounting for 50% of global exports as of 2025.

Rise of emerging economies: China and India’s integration into global supply chains increased trade in manufactured goods and outsourced services
Changing comparative advantage: Deindustrialisation in advanced economies shifted mass manufacturing production to low-wage emerging economies
Trading blocs and bilateral agreements: Reduced tariff barriers between member states increased intra-bloc trade by 30% on average
Exchange rate movements: Undervalued currencies in export-led economies (e.g. China pre-2015) made their goods more competitive globally
Rising protectionism: US-China trade war tariffs post-2018 reduced global trade volumes by 5% between 2018 and 2023

📐 Worked Example

Explain how the growth of the ASEAN free trade area has changed global trade patterns.

1
ASEAN eliminated tariff barriers between 10 Southeast Asian member states, reducing trade costs for intra-bloc firms.
2
This increased intra-ASEAN trade in intermediate goods, as firms specialise in parts of the electronics and automotive supply chains across member states to exploit comparative advantage.
3
Extra-bloc trade also increased, as ASEAN firms gained cost competitiveness from economies of scale, increasing their exports of finished goods to the EU and US by 40% between 2015 and 2025.

Exam tip:

Always reference real-world contexts (e.g. ASEAN, US-China trade war) when answering trade pattern questions to earn context marks in extended responses.

3. Terms of Trade★★★☆☆⏱ 7 min

📘 Definition

Terms of Trade (ToT)

ToT = \frac{\text{Export Price Index}}{\text{Import Price Index}} \times 100

Measures the volume of imports a country can buy per unit of exports. An increase in the index is an improvement in ToT; a decrease is a deterioration.

📐 Worked Example

A country’s export price index is 120 in 2024, and its import price index is 150. Calculate its 2024 terms of trade, and explain the impact of a 10% rise in export prices on export revenues, assuming demand for exports is price inelastic (PED = -0.4).

1
$\text{2024 ToT} = \frac{120}{150} \times 100 = 80$
2
10% rise in export prices makes new export price index = 132. New ToT = \frac{132}{150} \times 100 = 88, an improvement of 10%.
3
If PED for exports = -0.4 (inelastic), the 10% rise in price leads to a 4% fall in quantity demanded. Total export revenue increases, as the percentage rise in price is larger than the percentage fall in quantity sold.

Key influences on terms of trade include relative inflation rates (higher domestic inflation raises export prices, improving ToT), productivity growth (higher productivity reduces export prices, worsening ToT), exchange rate movements (currency depreciation reduces export prices in foreign currency, worsening ToT), and global commodity price changes (commodity exporters see ToT improve when global commodity prices rise).

Exam tip:

For 4-mark calculate questions, always show your full working including the formula, to get partial marks even if your final answer is incorrect.

4. Trade Liberalisation and Trading Blocs★★★☆☆⏱ 7 min

📘 Definition

Trading Bloc

A group of countries that agree to reduce or eliminate trade barriers between member states to increase trade and economic integration, with four main levels of integration.

Bloc Type	Key Features	Example
Free Trade Area	No tariffs/quotas on intra-bloc trade, independent external tariffs for non-members	USMCA (formerly NAFTA)
Customs Union	Free intra-bloc trade + common external tariff for all non-members	Mercosur
Common Market	Customs union + free movement of labour and capital between members	European Economic Area
Economic and Monetary Union	Common market + shared currency and coordinated macroeconomic policy	Eurozone

📐 Worked Example

Analyse the difference between trade creation and trade diversion when a country joins a customs union.

1
Trade creation occurs when high-cost domestic production is replaced by lower-cost production from other member states, increasing consumer welfare through lower prices and higher consumption.
2
Trade diversion occurs when low-cost production from non-member states is replaced by higher-cost production from member states, because the common external tariff makes non-member goods more expensive, reducing overall global welfare.

The WTO promotes global trade liberalisation by enforcing non-discrimination rules and negotiating multilateral tariff reductions. Conflicts between trading blocs and the WTO arise because blocs use discriminatory external tariffs against non-members, which can violate WTO most-favoured-nation rules and reduce global trade through trade diversion effects.

Exam tip:

For 8-mark examine questions on trading bloc costs and benefits, always include both trade creation and trade diversion points, and link them directly to welfare impacts.

5. Restrictions on Free Trade★★★★☆⏱ 8 min

📘 Definition

Tariff

A tax imposed on imported goods, which raises the domestic price of imports, protects domestic producers, and raises government revenue. The tariff diagram is a core required diagram for this topic.

📐 Worked Example

Explain the impact of a 10% tariff on imported steel on domestic consumers, producers, and the government, using a tariff diagram.

1
The tariff shifts the world supply curve of steel upwards, raising the domestic price from $P_{w}$ to $P_{w + t}$ .
2
Domestic consumers pay higher prices and reduce their quantity demanded of steel, losing consumer surplus.
3
Domestic steel producers receive a higher price, increase their output, and gain producer surplus.
4
The government earns tariff revenue equal to the volume of imports after the tariff multiplied by the tariff rate, represented by a rectangle on the diagram.
5
Two deadweight loss triangles arise: one from inefficient domestic production replacing low-cost imports, and one from lost consumption of steel at the higher price.

Infant industry protection: Shield new domestic industries from foreign competition until they gain economies of scale to compete globally
Protect domestic employment: Reduce import competition to prevent job losses in declining domestic industries
National security: Protect strategic industries (energy, defence) from reliance on politically unstable foreign suppliers
Prevent dumping: Stop foreign firms selling goods below production cost to drive domestic firms out of business
Correct trade deficits: Reduce import volumes to reduce the size of a current account deficit
Raise government revenue: Tariffs are a simple source of revenue for low-income economies with weak domestic tax collection systems

Exam tip:

For 20-mark evaluate questions on protectionism, always include evaluation points such as: effectiveness depends on PED for imports, risk of retaliatory tariffs from trading partners, and risk of domestic industry inefficiency if protection is permanent.

6. Common Pitfalls

Wrong move:

Confusing absolute and comparative advantage when explaining gains from trade

Why:

Gains from trade depend only on comparative advantage (lower opportunity cost), not absolute advantage (lower total cost). Mixing these up leads to incorrect analysis of specialisation outcomes.

Correct move:

Always calculate opportunity costs first when answering comparative advantage questions, and explicitly distinguish between the two terms if asked.

Wrong move:

Stating that an improvement in terms of trade always improves the balance of trade

Why:

An improvement in ToT means export prices rise relative to import prices, which can reduce export volumes if demand for exports is price elastic, leading to lower export revenues and a worse trade balance.

Correct move:

Always link terms of trade changes to the price elasticity of demand for exports and imports when analysing impacts on the trade balance.

Wrong move:

Mixing up trade creation and trade diversion when evaluating trading blocs

Why:

Trade creation increases welfare while trade diversion reduces welfare, so mixing these terms leads to incorrect evaluation of trading bloc impacts.

Correct move:

Use the mnemonic: Creation = Cheaper bloc imports replace expensive domestic production; Diversion = Dearer bloc imports replace cheap non-bloc production.

Wrong move:

Forgetting to label all required areas on the tariff diagram

Why:

Unlabelled or incorrectly labelled diagrams lose up to 2 marks per question, even if your written analysis is fully correct.

Correct move:

Always label axes, domestic S/D curves, $P_{w}$ , $P_{w + t}$ , consumer surplus loss, producer gain, government revenue, and deadweight loss triangles on tariff diagrams.

Wrong move:

Only presenting one-sided arguments for or against protectionism in extended responses

Why:

Extended response questions require balanced analysis and evaluation to reach top level marks, and one-sided answers are capped at low KAA marks.

Correct move:

Always include 3-4 KAA points for, 2-3 KAA points against, plus 3 evaluation points (magnitude, time lags, context) for 14 and 20-mark questions.

7. Quick Reference Cheatsheet

Concept	Key Fact/Formula	Exam Application
Comparative Advantage	Opportunity cost = (output of good A)/(output of good B)	Calculate opportunity costs first to identify specialisation gains
Terms of Trade	$T o T = \frac{Export Price Index}{Import Price Index} \times 100$	Improvement = higher export prices relative to import prices
Trading Blocs	FTA < Customs Union < Common Market < EMU (increasing integration)	Trade creation = welfare gain; trade diversion = welfare loss
Tariff Diagram	$P_{w}$ = world price; $P_{w + t}$ = price after tariff	Label deadweight loss triangles for full diagram marks
Protectionism	6 core reasons: infant industries, employment, security, anti-dumping, deficit, revenue	Add evaluation (retaliation, inefficiency, PED) for extended answers

8. Frequently Asked

Do I need to draw a comparative advantage PPF for 8-mark questions?

Yes, if the question asks to illustrate gains from trade, a fully labelled PPF or opportunity cost table with before/after specialisation figures will earn full KAA marks, provided you link it explicitly to your analysis.

What weight is evaluation in Unit 4 extended answers?

Evaluation makes up 30% of marks for Unit 4 (IA2) papers: 6 marks for 14-mark questions, and 8 marks for 20-mark questions. Top evaluation includes magnitude, PED, time lags, and clear, justified judgements.

Going deeper

What's Next

Now that you have mastered core trade content, move on to the next Unit 4 topic: balance of payments and exchange rates, which builds on your understanding of trade flows and terms of trade impacts. You should also practise past paper extended response questions on trade to refine your analysis and evaluation chains, making sure to use real-world context and correctly labelled diagrams to maximise marks. Focus on 14 and 20-mark evaluate questions, as these are the highest weight questions on this topic, and practise making clear, justified judgements to reach top level 5 marks.