CENSUSES OF POPULATION AND HOUSING (ABS)
Preceded by population musters and censuses of particular States, the first simultaneous population censuses of all the Australian colonies were taken in 1881 and the first national census was taken in 1911. It was followed by others in 1921, 1933, 1947, 1954 and 1961. Since 1961 they have been conducted at five yearly intervals. The censuses provide comprehensive population data including information on a wide range of socioeconomic characteristics and for a variety of geographic areas. These data are referred to as 'census counts' and are available as at census dates only. Since the expansion of ABS social survey program over recent decades much of the information collected in the census has also become available from other sources and often in greater detail. However, the census provides the essential basis needed to produce official estimates of the population at the national, State and local government levels as well as for regions and more detailed levels of geography. It also provides a great deal of flexibility in terms of deriving counts of small groups of interest and about people living in specific geographic localities in ways that are not possible from information collected in sample surveys.
Assisting with the task of producing population estimates and projections, the censuses also collect information about some of the components of population growth. These include information about people's place of residence at various times in the past which provides the basis for understanding levels and patterns of internal migration. Data on people's country of birth and their period of residence in Australia also supports the analysis of population change attributable to international migration. Studies on trends in fertility have also been supported by questions asking about the number of children ever born to women.
CENSUS POST-ENUMERATION SURVEY (ABS)
From the 1966 census, each census has been followed by a Post Enumeration Survey (PES), to measure the extent of undercount. The questions asked in the survey mainly relate to the characteristics of people in the household, including age, sex, country of birth and marital status, and where each household member could have been counted in the census. At each of these addresses (including the interview address), the personal information is matched to any corresponding census forms for these addresses to determine whether a person is counted, is counted more than once, or not counted at all. Results obtained in the PES are used to adjust census counts in the calculation of all Estimated Resident Population (ERP) figures for Australia, and enable an assessment of some aspects of census field operations including the extent to which dwellings were missed by census collectors.
REGISTRATIONS OF BIRTHS AND DEATHS
The registration of births and deaths in Australia has been compulsory since the middle of the nineteenth century when legislation was passed by the various colonies. Since federation, each State and Territory has maintained its own system of registration governed by independent legislation. The ABS obtains information from each of the State Registrars for statistical purposes. Data available from birth certificates that are published on an annual basis include: the month of birth, the sex of the child, their place of birth, whether they were involved in a multiple birth, their Indigenous status as well as information about their parents, such as their ages, country of birth and for mothers the number of children to which they had previously given birth. Key data items relating to deaths include the sex of the person, their age at death, the date on which they died, the place of death, the cause of death, the usual place of residence of the deceased, their Indigenous status and their country of birth.
RECORDS OF OVERSEAS ARRIVALS AND DEPARTURES
Good statistical records relating to overseas movement have been maintained since colonial days. This has been made possible by the relative isolation of Australia, the absence of direct land links with other countries and the limited number of ports of entry. There has also been relatively strict government control of arrivals and departures. Overseas arrivals and departures statistics have for a long time been compiled from information entered on incoming and outgoing passenger cards, and from visa and other information available to the Department of Immigration and Multicultural Affairs (DIMA). From these the ABS produces monthly statistics on numbers of short term visitor arrival and departures and annual statistics on long term and permanent arrivals and departures to and from Australia. Data items used for statistical purposes include those related to the travellers themselves (their age, sex, citizenship, country of birth and occupation) and those related to their journey, such as their arrival/departure date, their reason for travelling, their origin and destination (coded down to the State/Territory level when within Australia), and intended duration of residence or absence. DIMA also publishes a range of information about numbers of international movements including information about immigrants or 'settlers' who arrive in Australia under the various migration and humanitarian programs for which the government provides visas.
RECORDS OF INTERSTATE MOVEMENTS FROM MEDICARE
The Medicare system, established in 1986 to serve the large majority of Australia's population with various health care services, provides an on-going source of data on interstate migration that is used with other data to produce population estimates. The migration data is obtained by reference to the current and previous addresses of a person maintained on their membership registration records which can be compared for selected points in time. The data, available by age and sex, is known to have various problems (e.g. people do not always advise a change of address) so the data is not used directly to estimate internal migration - rather, internal migration estimates are modelled from the Medicare data. Because of the deficiencies in the data, statistics relating to internal migration obtained from Medicare are not separately published in their own right.
SYMPTOMATIC INDICATORS OF POPULATION GROWTH
Although annual births and deaths data are available for SLAs, the absence of suitable international and internal migration data for non-census years means that it is not possible to use the component method to update SLA population totals. Instead, population for most SLAs are estimated by applying a regression model. Symptomatic indicators are any available set of data which in some way relate to changes in population size. Various indicators are used to support the provision of SLA population estimates produced by the ABS and the choice varies between States. Examples of indicators used include, dwelling approvals, Medicare enrolments, drivers licenses allocated and electricity connections. The relationships between population growth and symptomatic indicators are expressed mathematically in terms of 'regression coefficients' and, with the knowledge of the growth in the indicators for the current time period, they enable population growth to be estimated.
LONGITUDINAL SURVEY OF IMMIGRANTS TO AUSTRALIA (DIMA)
During the early 1990s, DIMA established a longitudinal survey to assess the settlement experience of recent migrants to Australia. The first round of the survey began with a sample of visaed immigrants (aged 15 years and over) and their families, who had arrived in Australia between September 1994 and August 1995. Respondents were first interviewed after they had been in Australia for six months, and reinterviewed on two subsequent occasions (at eighteen months and three and a half years after their arrival) providing a series of information about them. Items of information included, the type of visa used to gain residency, their labour force experience, their English language skills, income, housing, sponsorship of relatives, health status, and satisfaction with life in Australia. Work has since been initiated to obtain a similar series of information for a second cohort of immigrants who arrived in Australia between 1 September 1999 and 31 August 2000.