Gross domestic product
Gross domestic product (GDP) is a monetary measure of the market value of all the final goods and services produced in a period of time, often annually 
GDP (nominal) per capita does not, however, reflect differences in the cost of living and the inflation rates of the countries; therefore using a basis of GDP per capita at purchasing power parity (PPP) is arguably more useful when comparing differences in living standards between nations.
List of countries by GDP (PPP) in the nineteenth century
Due to the absence of sufficient data for nearly all economies until the 20th century, earlier GDP is only roughly estimated. In a first step, economic historians try to reconstruct the GDP per capita of a given political or geographical entity from the meagre evidence. This value is then multiplied by the estimated population size, another determinant for which as a rule only little ancient data is available.