The Balassa-Samuelson Effect

Purchasing power parity says that after converting currencies, the same basket of goods should cost roughly the same everywhere. In practice it systematically fails for one category: services like haircuts, restaurant meals, and rent are far cheaper in poor countries than in rich ones, even after adjusting for the exchange rate. The Balassa-Samuelson effect explains why: it is not that rich-country barbers are lazy or overpaid, it is that rich-country manufacturing workers are so productive that wages get bid up economy-wide, including for barbers whose actual productivity hasn't changed at all.

Why it matters for FX

Because rich, fast-growing economies see their tradable-sector productivity rise faster than poor economies, the Balassa-Samuelson effect predicts their currencies should appreciate in real terms over time — a currency isn't "overvalued" just because a coffee costs more there than in a developing country; some of that gap is a structural, productivity-driven feature, not a mispricing to bet against.

Worked example

A manufacturing worker in Country A produces $50 of tradable goods per hour, versus $10/hour in Country B — a 5x productivity gap. Wages in A's tradable sector rise to match, pulling up wages for A's baristas and hairdressers too, even though a barista's output per hour hasn't changed anywhere. A basket of local services that costs $8 in Country B might cost $35 in Country A, a gap far larger than the wage-productivity difference in services alone — exactly the pattern Balassa-Samuelson predicts.