1 This product contains estimates of the resident population of Statistical Local Areas (SLAs) and Local Government Areas (LGAs) of Western Australia at 30 June 2005, by age and sex.
2 To meet the conflicting demands for accuracy and timeliness there are three estimates of sub-state/territory populations by age and sex: preliminary, normally available one year after the reference date; revised, normally available around 18 months after the reference date; and final, available after the following census. The estimates in this product are preliminary. Revised June 2005 sub-state/territory estimates are scheduled to be available 7 December 2006.
ESTIMATED RESIDENT POPULATION - AUSTRALIA
3 Estimated resident population (ERP), the official measure of the population of Australia, is based on the concept of residence. It refers to all people, regardless of nationality or citizenship, who usually live in Australia, with the exception of foreign diplomatic personnel and their families. It includes usual residents who are overseas for less than 12 months. It excludes overseas visitors who are in Australia for less than 12 months.
4 Estimates of the resident population are based on census counts by place of usual residence (excluding overseas visitors in Australia), with an allowance for net census undercount, to which are added the number of Australian residents estimated to have been temporarily overseas at the time of the census.
5 Population estimates are updated by adding to the estimated population at the beginning of each period the components of natural increase (births minus deaths, on a usual residence basis) and net overseas migration. For the states and territories, account is also taken of estimated interstate movements involving a change of usual residence.
6 After each census, estimates for the preceding intercensal period are finalised by incorporating an additional adjustment (intercensal discrepancy) to ensure that the difference between the ERPs at the two respective census dates agrees with the total intercensal change.
7 A more detailed explanation of the concept of ERP, as adopted by the ABS for official population estimates, is contained in Demographic Estimates and Projections: Concepts, Sources and Methods (cat. no. 3228.0).
ESTIMATION OF SLA-BASED POPULATIONS
8 In Australia, the SLA is the base spatial unit used to collect and disseminate statistics other than those collected from the Population Censuses. In non-census years, the SLA is the smallest unit defined in the Australian Standard Geographical Classification (ASGC). In aggregate, SLAs cover the whole of Australia without gaps or overlaps. Populations for SLAs are estimated as at 30 June each year. The population estimates for LGAs and other regions are built up from the SLA-level estimates.
9 The ERP as at census date for each SLA is calculated based on usual residence census counts, excluding overseas visitors in Australia, with an allowance for net census undercount and the number of residents temporarily overseas at the census date. The estimates of net undercount are apportioned to SLAs based on age, sex, Indigenous status, state and territory, and (for the six states) capital city/balance of state. The number of residents temporarily overseas on census night is estimated based on coding addresses of residence to SLA from a sample of incoming passenger cards. As the census is held on a date other than 30 June (the 2001 Census was held on 7 August), further adjustments taking into account births, deaths and migration for the intervening period are made to obtain the ERP at 30 June.
10 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, these ERPs are calculated using a mathematical model. All output from the model is scrutinised and validated by population analysts. Local knowledge, including that advised by local governments, may be used to adjust the outcome of the model for a particular SLA. In some areas population change since the previous census is assumed to be zero in the absence of reliable indicator data for these areas.
11 In the model, a relationship is established between changes in population and changes in indicators between the two most recent censuses. The choice of indicators varies across the states and territories, depending on availability and indicative ability, and includes dwelling approvals, electricity connections, Medicare enrolments and drivers' licences. The choice of indicators also varies within states/territories, depending on aspects such as whether the SLA is urban or rural, is growing or declining, and has a high or low proportion of medium- and high-density dwellings. Changes in these indicators are then used to estimate changes in the population of each area since the last census.
12 The total SLA population estimates for post-censal years are then broken down into age and sex components. The estimates by age and sex are updated from the previous year's estimates using registered births and deaths data, and synthetic estimates of migration based on the 2001 Census. For areas where this data is deemed to be of insufficient quality, adjustments are made. While the output is presented by five year age group (up to 80-84 years, then 85 years and over), all calculations are made at single year of age level (up to 84 years, then 85 years and over).
13 In recognition of the inherent inaccuracy involved in population estimation, population figures in accompanying text are generally rounded. While unrounded figures are provided in the main tables, accuracy to the last digit is not claimed and should not be assumed.
AUSTRALIAN STATISTICAL AREAS
14 This product contains data presented according to the Australian Standard Geographical Classification (ASGC) 2005 Edition, which refers to boundaries as defined at 1 July 2005. Under this classification, statistical areas are defined as follows:
Local Government Areas (LGAs). These areas are the spatial units which represent the geographical areas of incorporated local government councils. The ABS has broadened the categories of legislation used to define local government areas for statistical purposes to include the Indigenous Council areas in the states and Northern Territory. The LGA Structure covers only incorporated areas of Australia, which are legally designated parts of states and territories over which incorporated local governing bodies have responsibility.
Statistical Local Areas (SLAs). These geographical areas are, in most cases, identical with, or have been formed from a division of, whole LGAs. In other cases they represent unincorporated areas. In aggregate, SLAs cover the whole of a state or territory without gaps or overlaps. In some cases legal LGAs overlap Statistical Subdivision boundaries and therefore comprise two or three SLAs (Part A, Part B and, if necessary, Part C).
15 LGAs are proclaimed by various state and territory government authorities and changes are gazetted throughout the year. Presently, LGAs are used as the base on which SLAs are defined for the ASGC. Because this definition process takes time, some LGAs gazetted during the year leading up to an ASGC edition are not always processed in time for inclusion in that edition, and are instead included in a later edition.
16 Further information about statistical areas is contained in Australian Standard Geographical Classification (ASGC), 2005 (cat. no. 1216.0).
17 ABS products draw extensively on information provided freely by individuals, businesses, governments and other organisations. Their continued cooperation is very much appreciated; without it, the wide range of statistics published by the ABS would not be available. Information received by the ABS is treated in strict confidence as required by the Census and Statistics Act 1905.
18 Other ABS releases that may be of interest to users of this product include:
Regional Population Growth, 2004-05, cat. no. 3218.0.
Population by Age and Sex, Australian States and Territories, June 2005, cat. no. 3201.0
Australian Demographic Statistics, cat. no. 3101.0
Australian Historical Population Statistics, 2006, cat. no. 3105.0.65.001
National Regional Profiles
19 Current publications and other products released by the ABS are listed in the Catalogue of Publications and Products (cat. no. 1101.0).
The ABS also issues a daily Release Advice on the web site which details products to be released in the week ahead.
20 As well as the statistics included in this and related products, additional information is available from the ABS web site <www.abs.gov.au> by selecting Themes then People then Demography.