Core lesson
Comparative Advantage and Trade Evidence
Comparative advantage compares opportunity costs, not wages, productivity levels or export totals alone.
A two-good calculation
With one unit of resources, North can make 12 tonnes of grain or 6 machines; South can make 8 tonnes of grain or 8 machines. North gives up 2 tonnes of grain per machine, while South gives up 1. South has comparative advantage in machines; North has comparative advantage in grain even though North produces more grain absolutely.
A terms-of-trade rate between 1 and 2 tonnes of grain per machine can make both sides better off relative to their modeled opportunity costs, before transport, adjustment and distribution costs.
The model is a benchmark
- Resources may not move quickly between sectors, and workers bear unequal adjustment costs.
- Scale economies, market power, supply-chain risk and environmental externalities can matter.
- A country-level gain does not mean every household or region gains.
- Policy evaluation should state tariff coverage, retaliation, exchange rates and comparison period.
Read trade data by definition
Gross exports count the full border value and can count imported inputs embedded in exports. Value-added measures allocate income generated at each production stage. A bilateral trade balance is not a welfare score, and mirror statistics can differ because of timing, valuation and routing.
Mini practice
- Compute each opportunity cost in the example.
- Would 2.5 tonnes of grain per machine benefit North as a machine importer?
- Name one reason gross exports overstate domestic production.
- North: 2 grain/machine; South: 1 grain/machine.
- No. North can produce a machine by giving up only 2 tonnes.
- Imported intermediate inputs are included in the export value.
Sources
- OpenStax: Absolute and Comparative Advantage.
- UN Comtrade: product-level trade records and metadata.
- OECD Trade in Value Added.
Sources accessed 10 October 2026. Quantities are a teaching scenario, not country data.