The GNP per capita figures are calculated according to the World Bank Atlas method of converting data in national currency to US dollars. In this method, the conversion factor for any year is the average exchange rate for that year and the two preceding years, adjusted for differences in rates of inflation between the country and the United States. This averaging smooths fluctuations in prices and exchange rates. The resulting estimate of GNP in US dollars is divided by the midyear population to obtain the per capita GNP in current US dollars.
Formulas describing the procedure for computing the conversion factor for year t, and for calculating per capita GNP in US dollars for year t are available.
The conversion factor line on each country page reports the underlying annual observations used for this Atlas method. As a rule, it is the official exchange rate reported in the IMF'sInternational Financial Statistics (IFS), line rf.
Exceptions arise where World Tables recasts IFS style measures to report on a fiscal year basis or to average multiple exchange rates; in highly exceptional cases, further refinements are made by Bank staff. Country Conversion Factors lists all three exceptions).
Where multiple exchange rate practices are of ficially maintained and the spread between rates is analytically significant a transactions-weighted average is given, if possible. However, no account of unofficial parallel market rates is taken in the calculations. When the official exchange rate, including any multiple rate, is judged to diverge by an exceptionally large margin from the rate effectively applied to international transactions, a different conversion factor is used by the Bank. Where national compilers used an official exchange rate to assign a national currency value to international transactions, however, that rate must be used to convert the same items to dollars, regardless of whether it was the rate actually applied to international transactions. In these cases, country pages report both the conversion factor, underlying the Atlas method of converting values of international transactions, and an additional conversion factor underlying the Atlas method of converting the remaining components of GNP.
Current population estimates and estimates of fertility and mortality are made by the World Bank from data provided by the UN Population Division, the UN Statistical Office, country statistical offices, and other sources. In many cases, the data take into account the results of recent population censuses. Refugees not permanently settled in the country of asylum are generally considered to be part of the population of their country of origin.
Statistical background for the estimates is available in the UN annual Population and Vital Statistics Report and the Bank's annual World Population Projections.