EXPLANATORY NOTES
INTRODUCTION
1 This product contains estimates of the resident population of Statistical Areas Level 2 to 4 (SA2s - SA4s) and Greater Capital City Statistical Areas (GCCSAs) of Australia as at 30 June 2001 to 30 June 2011, by age and sex. These estimates plus those for Local Government Areas, Statistical Local Areas, Statistical Subdivisions and Statistical Divisions are also provided in the Downloads tab of this issue.
2 To meet the conflicting demands for accuracy and timeliness there are several versions of sub-state/territory population estimates. Preliminary estimates by age and sex as at 30 June are normally available by August of the following year, revised estimates the year after and rebased and final estimates after the following census. The estimates in this issue are final for 2001 to 2006 and preliminary rebased for 2007 to 2011, based on the results of the 2011 Census.
ESTIMATED RESIDENT POPULATION - AUSTRALIA
3 Estimated resident populations (ERPs) are official estimates of the Australian population, which link people to a place of usual residence within Australia. Usual residence is that place where each person has lived or intends to live for six months or more from the reference date for data collection.
4 Estimates of the resident population are based on census counts by place of usual residence (excluding short-term overseas visitors in Australia), with an allowance for census net undercount, to which are added the estimated number of Australian residents temporarily overseas at the time of the census.
5 Population estimates for Australia and the states and territories 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 More detailed explanations of the concept of ERP, as adopted by the ABS for official population estimates, are contained in Information Paper: Population Concepts, 2008 (cat. no. 3107.0.55.006) and Population Estimates: Concepts, Sources and Methods, 2009 (cat. no. 3228.0.55.001).
ESTIMATION OF SUB-STATE POPULATIONS
8 In July 2011, the ABS replaced the nation's official statistical geography, the Australian Standard Geographical Classification (ASGC) with the new Australian Statistical Geography Standard (ASGS). To assist users in the transition to the ASGS, population estimates by age and sex based on both the old and new geographies are contained within this issue.
9 In Australia, the SA2 (as defined in the ASGS) is now the base spatial unit used to collect and disseminate statistics other than those collected from the Population Census. In aggregate, SA2s cover the whole of Australia without gaps or overlaps. Populations for SA2s are estimated as at 30 June each year. Population estimates for larger regions are built up from SA2-level estimates. Under the ASGC, the base spatial unit for estimating population was the SLA.
10 The ERP as at census date for each SA2 by age and sex is calculated based on usual residence census counts, excluding short-term overseas visitors in Australia, with an allowance for census net undercount and the number of residents temporarily overseas (RTOs) at the census date. The estimates of net undercount are apportioned to SA2s based on age, sex, Indigenous status, state and territory, and broad region. The number of RTOs on census night is estimated based on coding addresses of residence to SA2 from a sample of incoming passenger cards. As the census is not held on 30 June (the 2011 Census was held on 9 August), further adjustments taking into account births, deaths and migration for the intervening period are made to obtain the ERP at 30 June. A procedure is then applied to avoid the release of unconfidentialised usual residence census counts while maintaining closeness to the unconfidentialised ERP.
11 For post-census years, the absence of migration data at the SA2 level means that it will not be possible to estimate SA2 populations by taking into account natural increase and net migration. Instead, ERPs for most SA2s will be calculated using a mathematical model, where relationships are established between changes in population and changes in indicator data between the two most recent censuses for groups of SA2s. Current indicators include dwelling approvals, Medicare enrolments and counts of people on the Australian Electoral Roll. Changes in these indicators will be used to estimate changes in the population of each area since the last census. In areas where indicator data is unreliable or migration can be assumed to be insignificant, population change may be estimated by adding natural increase (births minus deaths) since the previous census. In some very small areas population change since the previous census may be assumed to be zero in the absence of reliable indicator data for these areas. All estimates will be scrutinised and validated by ABS analysts. Local knowledge, including that advised by local governments, may be used to adjust the figures for particular SA2s. Estimates at SA2 level are constrained to state/territory population estimates. Under the ASGC, this method was applied at the SLA level.
12 Total population estimates for each SA2 for post-censal years will then broken down into age and sex components. The estimates by age and sex will be updated from the previous year's estimates using registered births and deaths data, and synthetic estimates of migration based on the previous census. For areas where these data are deemed to be of insufficient quality, adjustments will be made. While the output will be presented by five-year age group (up to 80 to 84 years, then 85 years and over), all calculations will be made at single year of age level (up to 99 years, then 100 years and over). Estimates at SA2 level will be constrained to state/territory population estimates.
13 To enable the comparison of regional populations by age and sex over time, historical population estimates based on consistent updated boundaries will be prepared. These estimates will correspond with previously-released estimates (on different boundaries) where possible. When official statistical boundaries, such as for Local Government Areas, are updated in future, historical estimates will be prepared based on the updated boundaries.
14 In census years, both preliminary total estimates (derived from updating the ERPs from the previous census) and rebased total estimates (based on the current census) are prepared. Differences between these two sets of estimates are referred to as intercensal errors. Rebased estimates of SA2 populations for previous intercensal years are based on estimates derived by apportioning the intercensal error evenly across the five years, while constraining the SA2 level estimates to state/territory estimates. Rebased 2007 to 2010 estimates were derived by adding one-fifth of the 2011 intercensal error to the previous estimates of the 2007 population, two-fifths to the previous estimate of the 2008 population, and so on.
15 In recognition of the inherent inaccuracy involved in estimating population, population figures in text and accompanying summary tables published by the ABS are generally rounded. In the commentary for this product, figures less than 1,000 are rounded to the nearest ten, figures over 1,000 are rounded to the nearest hundred, and figures over 1 million are rounded to the nearest 10,000 or 100,000. While unrounded figures are provided in the spreadsheets, accuracy to the last digit is not claimed and should not be assumed. Percentages and estimates of change in population are based on unrounded numbers.
16 Areas with a total population of less than 1,000 people at 30 June 2011 have been excluded from commentary in this issue.
AUSTRALIAN STATISTICAL AREAS
17 This publication contains data presented according to the 2011 edition of the Australian Statistical Geography Standard (ASGS), which refers to boundaries as defined at 1 July 2011. Under this classification, statistical areas are defined as follows:
- Statistical Areas Level 2 (SA2s). SA2s are medium-sized general purpose areas which aim to represent communities that interact together socially and economically. SA2s are based on officially gazetted suburbs and localities. In urban areas SA2s largely conform to one or more whole suburbs, while in rural areas they generally define the functional zone of a regional centre.
- Statistical Areas Level 3 (SA3s). SA3s are aggregations of whole SA2s and reflect a combination of widely recognised informal regions as well as administrative regions such as state government regions in rural areas and LGAs in urban areas.
- Statistical Areas Level 4 (SA4s). SA4s are made up of whole SA3s and are designed to reflect labour markets. In rural areas, SA4s generally represent aggregations of small labour markets with socioeconomic connections or similar industry characteristics. Large regional city labour markets are generally defined by a single SA4. Within major metropolitan labour markets SA4s represent sub-labour markets.
- Greater Capital City Statistical Areas (GCCSAs). GCCSAs are built from whole SA4s and represent a broad socioeconomic definition of each of the eight state and territory capital cities. They contain not only the urban area of the city, but also the surrounding and non-urban areas where much of the population has strong links to the capital city, through for example, commuting to work.
- Local Government Areas (LGAs). LGAs are ABS approximations of officially gazetted LGAs as defined by each state and territory local government department. LGAs cover incorporated areas of Australia, which are legally designated areas for which incorporated local governing bodies have responsibility. The ABS will update LGAs annually, and prepare updated and historical population estimates based on these updated boundaries.
18 Further information on these statistical areas is contained in
Australian Statistical Geography Standard: Volume 1 - Main Structure and Greater Capital City Statistical Areas, July 2011 (cat. no. 1270.0.55.001) and
Australian Statistical Geography Standard: Volume 3 - Non ABS Structures, July 2011 (cat. no. 1270.0.55.003).
POPULATION PYRAMID GRAPHS
19 Population pyramids are used throughout this product to illustrate the age and sex distribution of a population. In each case, five-year age groups are represented on the vertical axis of the graph. Some of the population pyramids show the number, in thousands, of males on the left horizontal axis and of females on the right horizontal axis. Most of the population pyramids, however, plot a percentage distribution on the horizontal axes. In those cases, the population in a particular age-sex group in an area is expressed as a percentage of the total population in that area. Thus, the sum of the percentages indicated by the bars of one colour in a population pyramid will be 100% of the population of the area represented by that colour, e.g. Greater Sydney. Further, the sum of the percentages indicated by the bars of the other colour will be 100% of the population of the area represented by the other colour, e.g. the rest of NSW. By using this method, the age and sex distribution of two areas can be compared irrespective of the relative sizes of the total populations of the areas.
ACKNOWLEDGEMENT
20 ABS publications 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.
RELATED RELEASES
21 Other ABS releases that are freely available on the ABS website <
www.abs.gov.au> and may be of interest to users of this product include:
ADDITIONAL STATISTICS AVAILABLE
22 As well as the statistics included in this and related publications, additional information is available from the ABS website <
www.abs.gov.au> by selecting Topics @ a Glance, People and then Demography.
23 In addition to the demographic data that are freely available on the ABS website, more detailed data can be obtained on request. For example, the data in this product can be prepared for different age groups, including single year of age, and geographic areas. Contact the National Information and Referral Service on 1300 135 070 to discuss your population data needs and request an obligation-free quote.
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