Population

I

Introduction

Population, term referring to the total number of human inhabitants of a specified area, such as a city, country, or continent, at a given time. Population study as an academic discipline is known as demography. It is concerned with: the size, composition, and distribution of populations; their patterns of change over time through births, deaths, and migration; and the determinants and consequences of such changes. Population studies yield knowledge important for short- and long-term planning, particularly by governments, in fields such as health, education, housing, social security, employment, and environmental preservation. Such studies also provide the information needed to formulate government population policies, which seek—among other things—to modify demographic trends in order to achieve certain economic and social objectives.

II

The Field of Demography

Demography is an interdisciplinary field involving mathematics and statistics, biology, medicine, sociology, economics, history, geography, and anthropology. The field of demography has a relatively brief history. Its beginning is often dated from the publication in 1798 of An Essay on the Principle of Population by the British economist Thomas Robert Malthus. In this work Malthus warned of the constant tendency for human population growth to outstrip food production and classified the various ways that such growth would, in consequence, be slowed. He distinguished between “positive checks” to population growth (such as war, famine, and disease) and “preventive checks” (celibacy and contraception).

The development of demography has been closely tied to the gradually increasing availability of data on births and deaths from parish and civil registers, and on population size and composition from the censuses that became common in the 19th century. The growth of the behavioural sciences in the 20th century and advances in the fields of statistics and computer science further stimulated demographic research. Sub-fields of mathematical, economic, and social demography have grown rapidly in recent decades.

III

Demographic Data and Measurements

Modern national governments and international organizations place a high priority on the accurate determination of national and worldwide populations. Describing the present population and predicting those of the future with reasonable accuracy requires reliable data.

A

Methods of Research

National censuses, civil registration, and, since the 1960s, national sample surveys are the major sources of demographic data. They provide the raw materials for investigating the causes and consequences of population changes. The most common source is the population census, a count of all people by age and with specified social and economic characteristics within a given area at a particular time. A register is a continuous record of births, deaths, migrations, marriages, and divorces, often maintained by a local government; reliability varies with the scrupulousness of citizens in reporting these data. In the sample survey, a statistically selected portion is used to represent the total population.

International population data are compiled in systematic form by the United Nations Statistical Division, which prepares an annual Demographic Yearbook; by the United Nations Demographic Division, which issues biennial assessments and projections of world population; and by the International Bank for Reconstruction and Development (World Bank). Other useful sources of information include the US Census Bureau, the United Nations Population Fund, and the Washington-based Population Reference Bureau.