Comparable measures of economic act

Comparable measures of economic activity, wealth and living standards are useful for many purposes. Foreign investors, traders, and potential immigrants want to know an economy’s market size, productivity and prices. The globalization of markets for goods, services, finance, labor and ideas reinforces the interdependence of economies and the need to measure them on a common scale. Countries cannot share responsibilities for global public goods—the environment, security, development assistance and global governance—without meaningful assessments of the real size of their economies and the wealth of their people. But comparing the real size of economies is not easy. Even in an integrated global economy, large differences in the costs of goods and services persist. Exchange rates can be used to convert values in one currency to another, but since they do not fully reflect differences in price levels, they cannot measure the real volume of output. Exchange rates are determined by the demand for and supply of currencies used in international transactions, ignoring domestic economic sectors where prices are set in relative isolation from the rest of the world—thus the familiar experience of international travelers, who discover that they can buy more, or less, of the same goods in different countries when converting their money using the prevailing exchange rates.