IB Economics HL onlyTopic 4 — The Global EconomyPaper 1 & 3Core skill~10 min read
Absolute and Comparative Advantage
Here is the idea that surprises most students: a country can be worse at making everything and still have something worth selling. What matters is not who is better in absolute terms, but who gives up least to produce each good. Get the opportunity cost right and the whole topic falls into place.
📚 What you need to know
Absolute advantage: a country can produce more of a good using the same factors of production than another country.
Comparative advantage: a country can produce a good at a lower opportunity cost than another country.
The theory comes from David Ricardo (1817): countries should specialise where their opportunity cost is lowest, then trade.
A country can hold an absolute advantage in both goods and still gain from trade.
A country cannot have a comparative advantage in both goods — the opportunity costs are mirror images.
Sources of comparative advantage: natural resources, the labour force, technology, capital and infrastructure, economies of scale, and government policy.
The theory rests on strong assumptions, and those assumptions are where your evaluation marks come from.
Two countries, two goods
Take Northland and Southland, each able to produce wheat or steel. Using all of its resources, Northland can make 900 thousand tonnes of wheat or 300 thousand tonnes of steel. Southland can manage 400 thousand tonnes of wheat or 200 thousand tonnes of steel.
Northland’s frontier lies outside Southland’s everywhere, which is exactly what absolute advantage in both goods looks like.
Working out the opportunity costs
Take one country at a time. Northland gives up 900 wheat to get 300 steel, so one tonne of steel costs three tonnes of wheat. Turn it upside down for the other good.
Opportunity cost
cost of 1 unit of good X = total possible Y ÷ total possible X
Compare down the row, not across the table. You are asking which country sacrifices less to make the same thing.
Students lose marks by comparing the wrong pair of numbers. Never compare Northland’s steel cost with Northland’s wheat cost. Compare Northland’s steel cost with Southland’s steel cost.
Where comparative advantage comes from
Natural resources — fertile land, minerals, energy, a good climate for a particular crop.
The labour force — its size, skills and cost. Skilled workers help in technology; cheaper labour helps in labour-intensive work.
Technology — better methods and research capacity lower the cost of producing the same output.
Capital and infrastructure — ports, roads, power and communications that let goods be made and moved cheaply.
Economies of scale — large output spreads fixed costs, cutting the cost per unit.
Government policy — trade agreements, tax incentives, support for research, protection of intellectual property.
Comparative advantage is not permanent. It shifts as technology, wages and infrastructure change, which is why countries that once dominated an industry can lose it within a generation.
The limits of the theory
Limitation
Why it matters
Transport costs are ignored
The model assumes moving goods is free. For heavy or perishable goods it clearly is not
Perfect knowledge is assumed
Countries are supposed to know their own and everyone else’s costs, which is unrealistic
Factors move easily
Workers and machines cannot switch from one industry to another as smoothly as the model implies
Costs are constant
Straight-line frontiers ignore economies of scale and rising costs as output grows
Structural unemployment
When an industry closes, its workers may not find work in the industry that expands
Over-dependence
Relying on another country for food, energy or components is risky if relations sour
Environmental damage
Negative externalities from more production and more transport are not counted at all
Unequal gains
Total income rises, but it can be distributed very unevenly within and between countries
Worked examples
WORKED EXAMPLE
Identifying comparative advantage from output figures
Using all its resources, Northland can produce 900 thousand tonnes of wheat or 300 thousand tonnes of steel. Southland can produce 400 thousand tonnes of wheat or 200 thousand tonnes of steel. Determine which country should specialise in which good. [4]
Step 1: opportunity costs for Northland1 steel = 900 ÷ 300 = 3 wheat1 wheat = 300 ÷ 900 = 0.33 steelStep 2: opportunity costs for Southland1 steel = 400 ÷ 200 = 2 wheat1 wheat = 200 ÷ 400 = 0.5 steelStep 3: compare each good across the countries
Steel: 2 is less than 3, so Southland. Wheat: 0.33 is less than 0.5, so Northland.
Southland specialises in steel, Northland in wheatNorthland has the absolute advantage in both goods, and it changes nothing.
WORKED EXAMPLE
Checking that both countries actually gain
The two countries agree to trade 1 tonne of steel for 2.5 tonnes of wheat. Explain whether both countries gain from this rate. [4]
Step 1: what does Northland gain?
Making steel itself costs Northland 3 wheat per tonne. Buying it costs only 2.5 wheat.
Step 2: what does Southland gain?
Making 1 steel costs Southland 2 wheat of lost output. Selling it earns 2.5 wheat.
Step 3: state the condition
Both gain because the trading rate sits between the two opportunity costs (2 and 3).
Yes — both countries gainOutside that range, one country would be better off producing the good itself and would refuse to trade.
💡 Exam tip
Write out all four opportunity costs before deciding anything. It takes thirty seconds and prevents the classic error.
Compare like with like: steel against steel, wheat against wheat.
Say “gives up” out loud when you write the cost. It keeps you in the language of opportunity cost.
Keep fractions as decimals to 2 d.p. unless the question says otherwise.
Label your PPC axes with units and mark both intercepts. Straight lines are fine here.
For evaluation, attack an assumption — transport costs, structural unemployment or over-dependence are the easiest three to develop.
⚠ Common mix-up
Treating absolute advantage as the answer. Producing more does not decide who should specialise.
Comparing the two goods within one country instead of one good across two countries.
Saying a country has a comparative advantage in both goods. Mathematically it cannot.
Forgetting to invert when moving to the second good.
Assuming specialisation is costless. Workers in the shrinking industry often become structurally unemployed.
Presenting the theory as proof that free trade is always best. The assumptions do a lot of quiet work.
Up next: Tariffs — the first and most commonly examined way governments interfere with all of this, and the diagram examiners ask for most often.
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