Top 20 Economies in 2030 (GDP PPP)
According to Wikipedia, GDP comparisons using PPP are arguably more useful than those using nominal GDP (see List of countries by GDP (nominal)) 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.