IB Economics: Free Trade & Comparative Advantage FAQ

You need the theory of comparative advantage (opportunity cost, not absolute output), how to calculate it from a production possibilities table, and the case for and against free trade — tariffs, quotas, subsidies, trading blocs, WTO rules. HL students also need the terms of trade diagram and PPC-based numerical proof.

Absolute advantage means producing more output with the same resources than another country. Comparative advantage means producing at a lower opportunity cost — giving up less of another good to make one unit of this good. Trade theory rests on comparative, not absolute, advantage: even a country worse at everything can still gain from trade.

Divide the output of one good by the output of the other, for each country, to find each country's opportunity cost. Whichever country has the lower opportunity cost for a given good holds the comparative advantage in producing it. Compare both goods to confirm each country specialises in a different one.

The model assumes constant opportunity costs (a straight-line PPC), no transport costs, perfect factor mobility within a country but zero mobility between countries, no externalities, and only two countries producing two goods. Real trade never fully matches these, which is exactly why evaluation marks reward you for questioning them.

Draw two PPCs, one per country, with the specialised good on the x-axis. Mark the pre-trade consumption point inside the PPC, then the post-trade consumption point outside it — this shows the country consuming beyond its own production possibilities. Label both axes, both points, and the direction of specialisation clearly.

For: lower prices, greater choice, efficiency gains from specialisation, economies of scale, and technology transfer. Against: structural unemployment in import-competing industries, over-reliance on a narrow export base, infant industries getting crushed before they mature, and environmental or labour-standard concerns in producing countries. Strong essays weigh these against the specific context in the question.

Paper 1 (SL and HL) tests it through data-response and essay questions — usually asking you to explain the theory and evaluate free trade using a real-world extract. Paper 3 (HL only) adds quantitative demands: calculating opportunity costs from a table, plotting the terms of trade, and interpreting numerical trade data under time pressure.

The most common one I see is confusing absolute advantage with comparative advantage in the opening paragraph — an instant loss of the knowledge and understanding marks. Others: forgetting to state which good each country should specialise in, and giving generic evaluation ("it depends") instead of a specific, contextualised limitation of the theory.

Tariffs and quotas are protectionist tools governments use precisely because unrestricted free trade based on comparative advantage can hurt specific domestic industries. A tariff diagram shows the welfare loss to society even as domestic producers and government revenue gain — the classic deadweight loss triangles examiners want you to shade and label.

Because total welfare gains don't guarantee gains for every group — free trade typically benefits consumers and export sectors while concentrated job losses hit import-competing workers hard and fast. Governments protect industries for political, strategic (national security, food security) and infant-industry reasons, even when the net welfare effect of doing so is negative.

Use examples you can actually explain in opportunity-cost terms rather than name-dropping countries. Bangladesh's textile specialisation, Chile's copper exports, or a regional trading bloc like the African Continental Free Trade Area all work well if you can state what each economy gives up to produce its specialised good.

It's conceptually simple but easy to get wrong under exam pressure — the opportunity cost calculation is basic arithmetic, but mixing it up with absolute advantage or misdrawing the trade diagram costs real marks. Students who drill the calculation and diagram until they're automatic tend to find this one of the more reliable topics for scoring well.

SL students need the theory, the diagram and qualitative evaluation of free trade. HL students need all of that plus the quantitative side: calculating comparative advantage from PPC tables, deriving terms of trade, and answering the structured calculation-based questions unique to Paper 3.

Past-paper Paper 1 essays give you the evaluation practice; Paper 3 past papers (HL) give you the calculation drilling you can't get any other way. On RevisionPrep, Topical Worksheets on international economics and the accompanying Revision Notes cover both the theory and the numerical PPC method with worked examples.