Appendix - Definitions, Sources, and Methods

Population estimates are based on the most recent demographic data available for each country and reflect the de facto population as of July 1st of the year indicated. Standard demographic techniques are used to estimate population for the base year (2005). For most countries, national population censuses are the main source of data; however, frequency and quality vary by country. Most countries conduct a complete enumeration no more than once a decade. Pre- and post-census estimates are interpolations or extrapolations based on demographic models. Surveys conducted by international organizations, such as the Demographic and Health Surveys Program, are often the source of the most recent demographic information for developing countries.

Data for charts 4.4 and 5.1 - 5.3 are from the United Nations. 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. Furthermore, ages are not always reported accurately, particularly in developing countries.

The dependency ratio (charts 4.4 and 5.3) is the ratio of dependents (persons under age 15 or over age 64) to the working-age population (persons ages 15 to 64). The dependency ratio is an overall measure of the dependence that children and the elderly have on people of working age. Whereas dependency ratios show the age composition of a population, they do not necessarily show economic dependency. Some children and elderly persons are part of the labor force and some working-age persons are not.

Data for 2025 are projected by applying assumptions regarding future trends in fertility, mortality, and migration. Because future trends cannot be known with certainty, a number of projection variants are produced by the United Nations. Data in charts 4.4 and 5.3 are based on the medium variant. For further information on the assumptions for the medium variant, see the source document.

The world population distribution (chart 5.1) shows each country’s share of the total world population. Total population of an economy includes all residents regardless of legal status or citizenship—except for refugees not permanently settled in the country of asylum, who are generally considered part of the population of their country of origin. The total population presents one overall measure of the potential impact of the country on the world and within its region.

The age composition of the population (chart 5.2) refers to the percentage of the total population that comprises the specific age group. Three age groups are presented in chart 5.2: persons under age 15, persons ages 15 to 64 (often referred to as the working-age population), and persons over age 64.

Source: United Nations, World Population Prospects: The 2006 Revision Population Database, http://www.un.org/esa/.