List of countries by GDP (nominal)
Gross domestic product (GDP) is the market value of all final goods and services from a nation in a given year. Countries are sorted by nominal GDP estimates from financial and statistical institutions, which are calculated at market or government official exchange rates. Nominal GDP does not take into account differences in the cost of living in different countries, and the results can vary greatly from one year to another based on fluctuations in the exchange rates of the country's currency. Such fluctuations may change a country's ranking from one year to the next, even though they often make little or no difference in the standard of living of its population.
List of countries by GDP (PPP)
GDP comparisons using PPP are arguably more useful than those using nominal GDP when assessing a nation's domestic market because PPP takes into account the relative cost of local goods, services and inflation rates of the country, rather than using international market exchange rates which may distort the real differences in per capita income. It is however limited when measuring financial flows between countries and when comparing quality of same goods among countries. PPP is often used to gauge global poverty thresholds and is used by the United Nations in constructing the human development index. These surveys such as the International Comparison Program include both tradable and non-tradable goods in an attempt to estimate a representative basket of all goods.