Public data, with its sources attached.

Published by the World Bank in English.

Statistical concept and methodology

Methodology: Population estimates are usually based on national population censuses, and estimates of fertility, mortality and migration. Errors and undercounting in census occur even in high-income countries. In developing countries errors may be substantial because of limits in the transport, communications, and other resources required to conduct and analyze a full census. The quality and reliability of official demographic data are also affected by public trust in the government, government commitment to full and accurate enumeration, confidentiality and protection against misuse of census data, and census agencies' independence from political influence. Moreover, comparability of population indicators is limited by differences in the concepts, definitions, collection procedures, and estimation methods used by national statistical agencies and other organizations that collect the data. The currentness of a census and the availability of complementary data from surveys or registration systems are objective ways to judge demographic data quality. Some European countries' registration systems offer complete information on population in the absence of a census. The United Nations Statistics Division monitors the completeness of vital registration systems. Some developing countries have made progress over the last 60 years, but others still have deficiencies in civil registration systems. International migration is the only other factor besides birth and death rates that directly determines a country's population change. Estimating migration is difficult. At any time many people are located outside their home country as tourists, workers, or refugees or for other reasons. Standards for the duration and purpose of international moves that qualify as migration vary, and estimates require information on flows into and out of countries that is difficult to collect. One of the major data sources of this indicator is UN Population Division's World Population Prospects, which use the cohort component method to produce population estimates and projections. Population projections, starting from a base year are projected forward using assumptions of mortality, fertility, and migration by age and sex through 2050, based on the UN Population Division's World Population Prospects database medium variant. Statistical concept(s): Estimates of total population describe the size of total population. Population estimates are dependent on the demographic components of change that are fertility, mortality and migration. As the size of population continues to change throughout the time even within a year, a reference time in the year that the estimate refers to is needed, such as mid-year, end-year or beginning of year. The values shown are midyear estimates.

Limitations and exceptions

Current population estimates for developing countries that lack (i) reliable recent census data, and (ii) pre- and post-census estimates for countries with census data, are provided by the United Nations Population Division and other agencies. The cohort component method - a standard method for estimating and projecting population - requires fertility, mortality, and net migration data, often collected from sample surveys, which can be small or limited in coverage. Population estimates are from demographic modeling and so are susceptible to biases and errors from shortcomings in both the model and the data. Because future trends cannot be known with certainty, population projections have a wide range of uncertainty.