Scope of Demography
To a statistician a population can be any collection of items but to a demographer it means a collection of people. Preston et al (2001:1) describe two such collections: • A population of persons alive at a particular point in time. For example, the 2001 Australian census collected information on all people in Australia on the night of Tuesday, August 7 th of August, 2001. • A population that ‘persists through time even though its members are continuously changing’. Demographers may thus talk about the aggregate of persons who have ever lived in Australia in the past and also about people in Australia in the future.
Populations can be subdivided, often by age and sex. For example, a study of the Australian labour force may look at males and females aged from 15 to 64 years. In a more restricted sense, a population can refer to any group being studied where its size and structure depend on persons entering and leaving (Pressat 1985:176). The composition of the Australian Defence Force largely depends on the entry of recruits and on members exiting on resignation (Schindlmayr and Ong, 2001).
The components affecting population change are measured by birth, death and migration rates that determine the numbers in the population, its age composition, and how fast it is growing or declining. If demographers are studying a country they will ask such basic questions as: How many males and females are there now? Where are they? What are their ages? How many births have occurred, and to whom? What are the characteristics of those who die or migrate? How and why will these change? 1 BEGINNING AUSTRALIAN POPULATION STUDIES BOX 1. Defining demography • Demography is the study of human populations in relation to the changes brought about by the interplay of births, deaths, and migration. The term is also used to refer to the actual phenomena observed, as in phrases such as the demography of tropical Africa (Pressat 1985:54). Demography is the statistical and mathematical study of the size, composition, and spatial distribution of human populations, and of changes over time in these aspects through the operation of the five processes of fertility, mortality, marriage, migration, and social mobility.
Although it maintains a continuous descriptive and comparative analysis of trends, in each of these processes and in their net result, its long-run goal is to develop a body of theory to explain the events that it charts and compares (Bogue 1969: 1-2). Demography is the study of the size, territorial distribution, and the composition of population, changes therein, and the components of such changes, which may be identified as natality, mortality, territorial movement (migration), and social mobility (change of status) (Hauser and Duncan 1959:2). • •
Note: In this last definition Hauser and Duncan (1959:2) explain that the omission of population quality is deliberate. Population composition refers not only to characteristics such as age, sex, and marital status but also to health and occupation. Social mobility involves changes in status e. g. through marriage and migration. The inclusion of social mobility as a part of demography can be disputed. Bogue (1969:28) includes it because ‘ there is very strong demographic component in this line of research’. John Graunt, who lived from 1620 to 1674, answered some questions of this ind for 17th century London. He estimated that London’s population comprised 199,000 males and 185,000 females, and that slightly more males than females had been born between 1628 and 1662 (Graunt 1975:57). Graunt was a cloth seller, and his knowledge of ‘shop arithmetic’ was the basis for his 1662 Natural and Political Observations, a study of births and deaths. His data were presented in statistical tables, their reliability was assessed and adjustments made (Kreager 1988). Because he calculated demographic rates and other statistics, Graunt is often called ‘the father of demography’.
In Australia pioneering effforts in demography included Pell’s 1867 paper on mortality rates (reproduced in Santow et al 1988) and the work of the first two Commonwealth Statisticians, Knibbs and Wickens (Gray 1998). Knibbs’s Mathematical