Comparative Advantage & Gains from Trade

You’ll be able to

Distinguish absolute advantage from comparative advantage
Calculate opportunity costs from output or input data to determine comparative advantage
Identify mutually beneficial terms of trade using the gains from specialization

Absolute vs. comparative advantage

When two producers can make the same goods, who should make what? Absolute advantage means producing more of a good with the same resources — being the outright more productive producer. But absolute advantage does not determine who should specialize. What matters is comparative advantage: producing a good at a lower opportunity cost than the other producer. A producer should specialize in the good for which it gives up the least, and then trade for the rest. Even a producer who is worse at everything (no absolute advantage) still has a comparative advantage in something, so trade can benefit both sides.

Finding comparative advantage from a table

Comparative advantage is decided by opportunity cost, so the first step is always to compute each producer’s opportunity cost for each good. With output data (units produced per period), the opportunity cost of good A is "how much B you give up per A" — that is, the other good’s output divided by this good’s output. The producer with the lower opportunity cost for a good holds the comparative advantage in it. Each producer will always have a comparative advantage in a different good (they cannot both be lower in both), which is exactly why specialization pays.

Opportunity cost from an output table

OC of 1 unit of Good A = (units of Good B produced) / (units of Good A produced)

Compute this ratio for each producer. Lower opportunity cost = comparative advantage. Remember "Other Over Own" when using output data.

Worked example

In one day, Country X can produce 10 wheat OR 20 cloth; Country Y can produce 8 wheat OR 8 cloth. Which country has the comparative advantage in each good, and what is a mutually beneficial trade rate for wheat?

1.Country X opportunity cost: 1 wheat = 20/10 = 2 cloth; 1 cloth = 10/20 = 0.5 wheat.
2.Country Y opportunity cost: 1 wheat = 8/8 = 1 cloth; 1 cloth = 8/8 = 1 wheat.
3.Wheat: X gives up 2 cloth, Y gives up 1 cloth → Y has the lower cost, so Y has the comparative advantage in wheat.
4.Cloth: X gives up 0.5 wheat, Y gives up 1 wheat → X has the lower cost, so X has the comparative advantage in cloth.
5.A beneficial trade rate for 1 wheat lies between the two opportunity costs: between 1 cloth (Y’s cost) and 2 cloth (X’s cost).

Answer: Country Y has the comparative advantage in wheat (cost 1 cloth vs. 2), and Country X in cloth (cost 0.5 wheat vs. 1). Any rate strictly between 1 and 2 cloth per wheat — for example 1.5 cloth per wheat — benefits both countries.

Checkpoint

In one hour Ana can make 6 pizzas or 3 salads; Ben can make 2 pizzas or 4 salads. Who has the comparative advantage in salads?

Watch out

Comparative advantage is decided by opportunity cost, not by who produces more. A producer with an absolute advantage in both goods still has a comparative advantage in only one — specialization is based on the lower-cost good for each.

Checkpoint

Two producers will both gain from trading one unit of good A for good B only if the agreed trade price is:

On the exam

On comparative-advantage problems, always compute opportunity costs first, then remember the shortcut for output tables: "Other over Own." Mixing up output and input data is the most common error — with input data (time or resources per unit) the ratio flips to "Own over Other."

Answer the 2 checkpoints as you read.