Real versus nominal value (economics)
Gross domestic product (GDP) is a measure of aggregate output. Nominal GDP in a particular period reflects prices which were current at the time, whereas real GDP compensates for inflation. Price indices and the U.S. National Income and Product Accounts are constructed from bundles of commodities and their respective prices. In the case of GDP, a suitable price index is the GDP price index. In the U.S. National Income and Product Accounts, nominal GDP is called "GDP in current dollars" (that is, in prices current for each designated year), and real GDP is called "GDP in [base-year] dollars" (that is, in dollars that can purchase the same quantity of commodities as in the base year).
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.