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Educerie · IB Diploma · Economics
Unit 4 The Global Economy · 4.1 Benefits of international trade
What you must be able to do
| You must be able to | Level | What it looks like in the exam |
|---|---|---|
| Explain the nine benefits of international trade | SL, HL | "Explain two benefits of international trade" (4 marks) |
| Draw free trade with imports, world price below the domestic price | SL, HL | Any diagram question, or the diagram inside a 10-mark part (a) |
| Draw free trade with exports, world price above the domestic price | SL, HL | The same, with the world price line drawn above equilibrium |
| Calculate imports, exports, import expenditure and export revenue from a diagram | HL only | Paper 3, two or three marks each, working shown |
| Explain absolute and comparative advantage, its sources and the gains from trade | HL only | Paper 1 part (a), or a Paper 3 explanation |
| Calculate opportunity costs from data to identify comparative advantage | HL only | Paper 3, with a table you build yourself |
| Draw a linear PPC showing different opportunity costs and the gains from trade | HL only | Paper 3; full marks only with the trading line on it |
| Evaluate the limitations of the theory of comparative advantage | HL only | The evaluation half of a 15-mark part (b) |
Before you start
You need the production possibility curve from Unit 1, because the HL half is built on it, and opportunity cost as a number rather than a feeling. You also need supply, demand and equilibrium from Unit 2: every diagram here is an ordinary market diagram with one extra horizontal line across it.
1The idea in one paragraph
A country that trades is no longer stuck with what it can make. It can buy at the world price instead of its own, sell at the world price instead of its own, and move its workers and machines into whatever it is relatively good at. Two diagrams show what happens to one market when it opens, one for a good the country imports and one for a good it exports. The nine benefits are those two diagrams added up across a whole economy.
2Free trade, the world price, and what it does to a market
International trade is the exchange of goods and services across national borders, and free trade means trade with no government barrier in the way: no tariff, no quota, no licence. Section 4.2, Types of trade protection, adds the barriers, so this is the picture before any of that.
Autarky is a country with no trade at all, so its price is whatever its own supply and demand produce. The world price is what the good sells for on the world market, written P world on your diagram.
Assume the country is small enough that its own buying and selling does not move the world price. That is what lets you draw the world price as a flat horizontal line. Everything then follows from one comparison: is the world price below the domestic price, or above it?
3Imports: the world price is below the domestic price
Take the sugar market in one country. Its own supply and demand meet at $60 a tonne and 40 thousand tonnes a year. It opens to trade, and the world price turns out to be $30.
Read Figure 1 in three steps, in this order, every time.
The price falls to the world price. No domestic buyer pays $60 for sugar available at $30 from abroad.
Find the two quantities on the world price line. Read across to the supply curve: domestic firms supply 10 thousand tonnes at $30. Read across to the demand curve: buyers want 70 thousand. Call these Qs and Qd.
The gap is imports. Imports are the quantity a country buys from the rest of the world, 60 thousand tonnes here, drawn as the horizontal distance between the two curves at the world price.
Consumers pay less and get more. Domestic producers sell less, 10 instead of 40, and at a lower price. That split is why 4.3 exists: opening a market can make a country better off overall while making an identifiable group inside it worse off.
4Exports: the world price is above the domestic price
Now the same country's cotton market, where supply and demand meet at $50 a tonne and 40 thousand tonnes. The world price is $70.
The three steps run the same way, reversed. The price rises to $70, because no farmer sells at $50 at home when foreign buyers pay $70. At $70 domestic firms supply 60 thousand tonnes and domestic buyers want only 20 thousand. The gap of 40 thousand is exports, the quantity a country sells to the rest of the world, again a horizontal distance at the world price.
Producers now sell more at a higher price; consumers pay $70 for what cost $50. Opening a market to exports raises the domestic price, and students forget that constantly, because "exports are good" sounds as though it should be good for everybody.
5The nine benefits of international trade
The guide names nine. They are easier to hold sorted by who feels them, which is what Figure 3 does.
Increased competition. Firms that were the only sellers now face foreign rivals, so they can no longer set a price and be sure of it.
Lower prices. Figure 1 is this benefit drawn: $60 down to $30, because the good can be bought where it is made most cheaply.
Greater choice. A closed market carries what domestic firms make; an open one carries what the world makes.
Acquisition of resources. Trade brings in raw materials, components, equipment and skills a country cannot produce at home at a sensible cost. A country with no oil can still run a transport system.
More foreign exchange earnings. Exports are paid for in foreign currency, and those earnings buy the imports. A country short of foreign exchange cannot buy machinery, medicines or fuel however much it wants them.
Access to larger markets. A firm selling only at home is capped by its own population; a firm that exports sells to the world.
Economies of scale. Falls in average cost as output rises, following straight from the last benefit. Say the chain out loud: bigger market, bigger output, lower average cost, lower price.
More efficient resource allocation. Land, labour and capital move into the industries where they are worth most, rather than spread thinly across everything the country needs.
More efficient production. Once resources have moved, output rises with no new resources found at all.
The last two cause the other seven, so a strong answer reaches them.
6HLReading quantities and money off the trade diagram
SL students can stop here. HL students turn the diagram into numbers, and Paper 3 pays for the working as well as the answer.
Quantity of imports = Qd − Qs at the world price, so in Figure 1, 70 − 10 = 60 thousand tonnes. Quantity of exports = Qs − Qd at the world price, so in Figure 2, 60 − 20 = 40 thousand tonnes.
The money versions are rectangles.
Import expenditure = world price × quantity of imports. Export revenue = world price × quantity of exports.
The shaded rectangle in Figure 4 is 60 thousand tonnes wide and $30 tall, so import expenditure is $30 × 60,000 = $1,800,000 a year, money leaving for foreign suppliers.
In Figure 5, export revenue is $70 × 40,000 = $2,800,000 a year, money coming in.
Two traps cost marks. The rectangle runs from Qs to Qd, not from zero: it is the traded quantity, not the whole market. And its height is the world price, not the old domestic price.
7HLAbsolute and comparative advantage
Two countries, Marovia and Tessala. Using all its resources for a year, each could produce:
| Wheat (thousand tonnes) | Solar panels (thousands) | |
|---|---|---|
| Marovia | 120 | 240 |
| Tessala | 100 | 50 |
Absolute advantage is producing more of a good with the same resources. Marovia has it in both, 120 against 100 and 240 against 50. If that were the whole story these two would have no reason to trade.
Comparative advantage is producing a good at a lower opportunity cost than another country. Opportunity cost is what you give up, so the question is never "who is better at this?" but "who gives up least to do this?"
Marovia can have 120 thousand tonnes of wheat or 240 thousand panels, so one tonne of wheat costs it 240 ÷ 120 = 2 panels and one panel costs 120 ÷ 240 = 0.5 tonnes. Tessala can have 100 tonnes or 50 panels, so one tonne of wheat costs it 0.5 panels and one panel costs 2 tonnes.
| Opportunity cost of 1 tonne of wheat | Opportunity cost of 1 panel | |
|---|---|---|
| Marovia | 2 panels | 0.5 tonnes of wheat |
| Tessala | 0.5 panels | 2 tonnes of wheat |
Read down the columns, not across. Wheat costs Tessala less, so Tessala has the comparative advantage in wheat. Panels cost Marovia less, so Marovia has the comparative advantage in panels. That table, read down the columns, is where the calculation marks sit.
Specialise in what you give up least to produce, not in what you are best at producing.
Marovia's line lies entirely outside Tessala's: absolute advantage, more of everything. The lines have different slopes: comparative advantage. Trade is worth doing whenever the slopes differ, whichever line is higher.
Now the gains. Before trade, say Marovia produces 30 thousand tonnes of wheat and 180 thousand panels, and Tessala 60 thousand tonnes and 20 thousand panels: 90 thousand tonnes and 200 thousand panels between them. Each specialises. Marovia makes only panels, 240 thousand; Tessala only wheat, 100 thousand tonnes. Between them, 100 thousand tonnes and 240 thousand panels — ten thousand more tonnes and forty thousand more panels from the same resources. Nothing was invented; the work moved to where it cost least.
They trade at terms of trade of one panel for one tonne, swapping 35 thousand of each.
| Wheat before | Panels before | Wheat after | Panels after | |
|---|---|---|---|---|
| Marovia | 30 | 180 | 35 | 205 |
| Tessala | 60 | 20 | 65 | 35 |
Both end with more of both goods, and both consume outside their own production possibility curve, which no country manages alone. The dashed trading line makes the gain visible: it runs from the specialisation point with a slope equal to the terms of trade.
One detail decides full marks. The terms of trade must sit between the two opportunity costs, here between 0.5 and 2 panels per tonne. At exactly 2 Marovia gains nothing, at 0.5 Tessala gains nothing, and outside that range one country would rather not trade.
8HLWhere comparative advantage comes from
The theory says specialise where opportunity cost is lowest, but not why one country's is lower. The guide asks you to know the sources. Factor endowments: how much land, labour, capital and enterprise a country has, and of what kind. Climate and geography: growing seasons, rainfall, mineral deposits, a deep-water port. Technology and the capital stock, which lower the cost of one industry relative to others at home. Human capital, the education and skills of the workforce. Infrastructure and institutions — roads, power, ports, courts that enforce contracts — which lower costs unevenly and so change relative costs too.
Two of these are built rather than found: human capital and technology. That matters for 4.3, because it means comparative advantage is not fixed forever.
9HLThe limitations of the theory of comparative advantage
This section is AO3, so the exam wants judgement, not a list. The theory is not wrong; it is a model, and a model is a set of assumptions. Naming one and saying what happens when it fails is what an evaluation mark pays for.
Two countries and two goods. The real world has around two hundred countries and millions of products, many of them parts crossing borders repeatedly before they are finished. The principle survives; the neat table does not.
No transport costs. Freight, insurance and delay can swallow a small cost advantage, which is why heavy, cheap goods such as sand and bricks are traded far less than light, valuable ones.
Resources move freely between industries. This assumption fails hardest. When a country stops making steel and starts writing software, the steelworkers do not become programmers; they become unemployed, often in a region with no other large employer. The gains from trade are real and spread thinly across millions of consumers; the losses are real too and land heavily on particular people in particular places.
Constant opportunity costs. A straight PPC says the millionth tonne of wheat costs the same as the first. Costs usually rise as an industry expands, because the best land and workers go first, which is why countries rarely specialise completely as the model says they should.
No protection anywhere, and advantage is fixed. Tariffs, quotas and subsidies exist, and 4.2 is the whole reason why: an industry can be lost to a rival that is better subsidised rather than genuinely cheaper. And since advantage can be built, an industry that cannot compete today might have competed in twenty years — the infant industry argument you meet in 4.3.
Nothing is said about who gains inside a country. The theory compares national totals and is silent on distribution, working conditions, environmental damage, or whether a country wants to depend on a single crop.
10Where marks are lost
Shifting a curve when the world price arrives. Neither curve moves. Domestic S and D stay put and the world price line is drawn across them.
Measuring imports vertically. Imports and exports are a horizontal distance in units of the good, read along the world price line. A vertical gap here is a price difference.
Thinking exports lower the domestic price. They raise it, as Figure 2 shows. The good becomes worth more at home once it can be sold abroad.
Using absolute advantage to decide who specialises. The country better at both goods still gains by specialising. Answer the opportunity cost question.
Reading the opportunity cost table across instead of down. Compare the same good between the two countries. Comparing two goods within one country says nothing about who should trade with whom.
Multiplying by the wrong price or quantity. Import expenditure uses the world price and the imported quantity only, never the domestic price or total consumption.
Treating the limitations as proof the theory is worthless. An evaluation says where the model holds, where it does not, and what a government should conclude.
11Draw it right
- Axes labelled with the good and its units, price vertical: sugar in thousand tonnes per year, price in dollars per tonne.
- Domestic S and D labelled and crossing at the autarky price. Mark that price and quantity even when the question is about trade.
- The world price as a dashed horizontal line across the whole diagram, labelled P world.
- Both quantities marked on it: Qs where it cuts supply, Qd where it cuts demand, with dotted lines to the quantity axis.
- The gap between them labelled imports or exports, with an arrow and its size written in.
- For an HL money question, the rectangle shaded from Qs to Qd, from zero up to the world price, with the multiplication beside it.
- For a PPC question, both lines with numbered intercepts, the specialisation point marked, and the dashed trading line from it. Without that line the diagram cannot show a gain.
12Try it
Marks in brackets. Answers and marker's notes are at the end. Do them before you look.
Q1. Using a diagram, explain what happens to domestic production, domestic consumption and the domestic price when a country whose domestic price is above the world price opens to free trade. 4 marks
Q2. Explain two benefits, other than lower prices, that a country may gain from international trade. 4 marks
Q3 (HL). At the world price of $25 a crate, domestic firms supply 15 thousand crates a year and domestic consumers buy 55 thousand. Calculate the quantity of imports and the import expenditure. 4 marks
Q4 (HL). Using all its resources, Alta can produce 60 thousand tonnes of maize or 180 thousand bicycles a year, and Brema can produce 40 thousand tonnes of maize or 40 thousand bicycles. Calculate the opportunity cost of one tonne of maize in each country and identify which has the comparative advantage in maize. 4 marks
Q5 (HL). Explain two limitations of the theory of comparative advantage. 4 marks
13In one breath
Trade lets a country buy and sell at the world price instead of its own. If the world price is below the domestic price, the price falls, firms supply less, consumers buy more, and the gap is imported; if it is above, the price rises, firms supply more, consumers buy less, and the gap is exported. Both gaps are horizontal distances at the world price. The nine benefits are competition, lower prices, choice, resources, foreign exchange, larger markets, economies of scale, better allocation and more efficient production. HL: multiply either gap by the world price for import expenditure or export revenue; absolute advantage is producing more, comparative advantage is giving up less, and specialising on the second lets both countries consume outside their own PPC.
Answers
Q1. The domestic price falls to the world price, because no consumer pays more at home for a good available more cheaply abroad. At that lower price domestic producers move down the supply curve to Qs, while domestic consumers move along the demand curve to Qd. The difference is met by imports. The diagram shows domestic S and D crossing at the autarky price, a horizontal world price line below it, and the gap between the curves at that line labelled as imports. 1 for the price falling to the world price, 1 for domestic supply falling, 1 for domestic consumption rising, 1 for a correctly labelled diagram showing imports as the horizontal gap. An answer that shifts either curve scores a maximum of 2.
Q2. Any two, each named and then explained. For example: access to larger markets means a firm is no longer limited by the size of its own population, so it can sell worldwide and raise output. Economies of scale follow, because as output rises average cost per unit falls, allowing a lower price. 1 for naming each benefit from the guide's list, 1 for a developed explanation of each. Four benefits named with no explanation scores 2.
Q3 (HL). Imports = quantity demanded − quantity supplied at the world price = 55,000 − 15,000 = 40,000 crates a year. Import expenditure = world price × quantity of imports = $25 × 40,000 = $1,000,000 a year. 1 for the method for imports, 1 for 40,000 crates, 1 for the method for expenditure, 1 for $1,000,000 with units. Multiplying $25 by 55,000 scores 1, for method only.
Q4 (HL). In Alta, one tonne of maize costs 180 ÷ 60 = 3 bicycles. In Brema, one tonne costs 40 ÷ 40 = 1 bicycle. Brema gives up fewer bicycles per tonne, so Brema has the comparative advantage in maize, even though Alta has an absolute advantage in both goods. 1 for each opportunity cost correctly calculated with units, 1 for comparing the same good across the two countries, 1 for identifying Brema. Choosing Alta because its output is larger scores a maximum of 2.
Q5 (HL). Any two, each named and then developed. For example: the theory assumes resources move freely between industries, but workers released by a declining industry often lack the skills the expanding one needs, so specialisation can produce long-term structural unemployment rather than a smooth reallocation. It also assumes no transport costs, but freight and insurance can cancel a small cost advantage, which is why bulky low-value goods are traded far less than the theory alone predicts. 1 for naming each limitation, 1 for explaining the consequence of each. A list of assumptions with no consequences scores 2.
Educerie · written from the published IB Diploma Programme Economics guide, first assessment 2022, section 4.1 Benefits of international trade. Original text, examples and questions. Diagrams drawn by Educerie. Last reviewed 10 September 2026.