National currency GDP is converted into U.S. dollars at the relevant year's conversion rate. However, where the official exchange rate is judged to diverge by an exceptionally large margin from the rate effectively applied to domestic transactions of foreign exchange and internationally traded products, a Bank-staff estimated exchange rate is used. Population Population is a World Bank estimate for mid-year population, based, in most cases, on a de facto definition, which counts all residents regardless of legal status or citizenship. Note, however, that refugees not permanently settled in the country of asylum are generally considered to be part of the population of their country of origin. Population estimates are usually based on national censuses, but the frequency and quality of these censuses vary by country.
Most countries conduct a complete enumeration no more than once a decade.
Precensus and postcensus estimates are interpolations or extrapolations based on demographic models. Moreover, the international comparability of population indicators is limited by differences in the concepts, definitions, data collection procedures, and estimation methods used by national statistical agencies and other organizations that collect population data. Current population estimates for developing countries that lack recent census-based population data, and precensus and postcensus estimates for countries with census data, are provided by national statistical offices or by the United Nations Population Division. The estimation methods require fertility, mortality, and net migration data, which are often collected from sample surveys, some of which may be small or have limited coverage. These estimates are the product of demographic modeling and so are also susceptible to biases and errors due to shortcomings of the model, as well as the data.