Purchasing Power Parity

Purchasing power parity (PPP) compares currencies by what they can buy, rather than only by their foreign-exchange value. A PPP conversion factor adjusts for differences in countries' price levels, allowing expenditure or output to be expressed in a common unit with comparable purchasing power. This makes comparisons of material living standards more meaningful than comparisons based solely on market exchange rates.

Why exchange-rate comparisons can mislead

Converting national income into dollars at the market exchange rate does not necessarily show how much people can consume locally. Exchange rates reflect factors such as capital flows and currency-market conditions, while many goods and services have different prices across countries.

• Locally supplied services, such as haircuts, can cost substantially less in lower-price economies, so the same dollar-converted income can buy different quantities.
• Consequently, exchange-rate-based income comparisons can understate the purchasing power of residents of lower-price countries.

How PPP creates a common purchasing-power measure

PPP calculations compare prices of comparable goods and services across countries and aggregate them using expenditure weights. The International Comparison Program, coordinated globally by the World Bank, produces internationally comparable PPP estimates.

• In a simplified illustration, if an identical basket costs ₹2,000 in India and $100 in the United States, its implied PPP is ₹20 per dollar; this is not an actual estimate.
• Dividing expenditure in domestic currency by its PPP conversion factor removes differences attributable to national price levels.
• An international dollar has the purchasing power over GDP that a US dollar has in the United States.
• Unlike a market exchange rate, PPP is a statistical conversion factor, not a rate at which currency can necessarily be exchanged.

What PPP reveals about living standards, and its limits

PPP-adjusted GDP per capita compares average output per person after accounting for price-level differences. It therefore provides a better indication of relative material resources than GDP per capita converted at market exchange rates.

• PPP-adjusted household consumption can provide a more direct comparison of goods and services consumed by households than GDP, which also includes investment and other expenditure.
• An average does not reveal income distribution, so similar PPP-adjusted GDP per capita can coexist with different levels of poverty and inequality.
• PPP comparisons remain sensitive to price-data quality, product comparability and differences in consumption patterns.
• PPP-adjusted GDP is not a complete welfare measure: health, education, environmental quality and unpaid activities also matter for living standards.