3.1. Population estimates at sub-State level are compiled for geographical areas known as Statistical Local Areas (SLAs) in accordance with the Australian Standard Geographical Classification (ASGC). These SLAs, which conform to, or combine to form Local Government Areas (LGAs), are the basic unit of a hierarchy of geographic areas within each State for which estimates are compiled. (For more details see the Glossary).
3.2. While national and State population estimates are compiled quarterly, SLA estimates are compiled for 30 June each year only. All SLA estimates are constrained to add to their respective State population totals.
3.3. Population estimates are referred to as either preliminary, revised or final. Preliminary estimates are generally made available 6 to 12 months after the reference period. Revised estimates are generally available each November for the financial year ending in the previous year (eg. revised estimates for the 30 June 1997 would be available in November 1998). Final estimates are published for the previous intercensal period after each census.
3.4. An age/sex disaggregation of all SLA population estimates has been produced annually since 1986. The estimates are published in five year age groups and are also available by single years of age.
3.5. In those cases where boundaries have changed, SLA population estimates and their components (births, deaths, and migration) produced since the beginning of the last intercensal period are adjusted to reflect current boundaries, for the purpose of time-series analysis.
3.6 In Census years the estimated resident population (ERP) as at 30 June for each Statistical Local Area (SLA)/Local Government Area (LGA) is based on usual residence census counts. To these counts are added an adjustment for net census undercount and the number of residents temporarily overseas at the Census date. As the 1996 Census was held on 6 August, further adjustments were made to obtain the ERP at 30 June 1996. Details of these adjustments are described below.
3.7. For post-censal years, the absence of migration data at the SLA level means that it is not possible to estimate SLA populations by taking into account natural increase and net migration. Instead, ERPs are calculated using a mathematical model. Local knowledge, including that advised by local governments, may be used to adjust the outcome of the model for a particular SLA.
3.8. In the mathematical model a relationship is established between changes in population and changes in other indicators over the period between the two most recent censuses. The choice of indicators varies across the States depending on availability, and includes dwelling approvals, electricity connections, Medicare enrolments and drivers licenses. Changes in these indicators are then used to estimate changes in the population of each area since the last census. The choice of indicators also varies across SLAs depending on aspects such as whether the SLA is urban or rural, is growing or declining, and whether the area has a high or low proportion of houses or medium and high density dwellings.