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EXPLANATORY NOTES


INTRODUCTION

1 This product contains estimates of the resident population of Statistical Areas Levels 2 to 4 (SA2s - SA4s) and Greater Capital City Statistical Areas (GCCSAs) of Australia as at 30 June 2001 to 30 June 2013, by age and sex. These estimates plus those for Local Government Areas are provided in the Downloads tab of this issue.

2 To meet the competing demands for accuracy and timeliness, there are several versions of sub-state 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 2011, revised for 2012 and preliminary for 2013.


ESTIMATED RESIDENT POPULATION - AUSTRALIA

3 Estimated resident population (ERP) is the official estimate of the Australian population, which links people to a place of usual residence within Australia. Usual residence within Australia refers to that address at which the person has lived or intends to live for six months or more in a given reference year.

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. After each Census, estimates for the preceding intercensal period are finalised (rebased) by incorporating an additional adjustment (intercensal difference) to ensure that the difference between the ERPs at the two respective Census dates agrees with the total intercensal change.

6 Throughout 2013, the ABS conducted a one-off exercise to revise (recast) population estimates for a longer time period, back to 1991. This was necessary due to a significant improvement in the methodology used to estimate net undercount in the 2011 Census. For more information, refer to the 20 June 2013 release of Australian Demographic Statistics, Feature Article 2: Recasting 20 years of ERP.

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 (cat. no. 3107.0.55.006) and Population Estimates: Concepts, Sources and Methods (cat. no. 3228.0.55.001).


ESTIMATION OF SUB-STATE POPULATIONS

8 In Australia, the SA2 (as defined in the Australian Statistical Geography Standard (ASGS)) is 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.

9 The ERP as at Census date for each SA2 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 provided by the Department of Immigration and Border Protection. 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.

10 For post-Census years, the absence of migration data at the SA2 level means that it is not possible to estimate SA2 populations by taking into account natural increase and net migration. Instead, ERP for most SA2s is 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 are 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 are 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 the SA2 level are constrained so that they add to the relevant state/territory population estimates.

11 Total population estimates for each SA2 for post-censal years are then disaggregated 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 previous Census. For areas where these data are deemed to be of insufficient quality, adjustments are made. A procedure is applied to confidentialise the sub-state estimates, which are also subsequently constrained so that they add to the relevant state/territory population estimates. As a result of this confidentialisation method, and forced additivity, estimates of under three people should be regarded as synthetic and only exist to ensure additivity to higher levels. While output is presented by five-year age group (up to 80 to 84 years, then 85 years and over), all calculations are made at single year of age level (up to 99 years, then 100 years and over). Population estimates based on single year of age are available on request as a charged consultancy.

12 The Statistical Area Level 1 (SA1) is the smallest unit for the release of Census data. There are approximately 55,000 SA1s and they cover the whole of Australia without gaps or overlaps. To provide some indication of estimated resident population below the SA2 level, the ABS prepares population estimates for SA1s. These estimates can be aggregated to form population estimates for regions such as State Suburbs, Remoteness Areas and Electoral Divisions. By this means, population estimates for areas other than those provided in this product (including SA1 ERPs) are available on request as a charged consultancy.

13 Population estimates at the SA1 level as at 30 June of a Census year are compiled by apportioning the estimate for each SA2 across the SA1s within the SA2, using Census usual residence counts, by age and sex. In post-Census years, the 30 June total population estimates for SA2s are apportioned across SA1s by taking into account population change implied by indicator data at the SA1-level in the years following the Census. For each SA1, the age/sex breakdown of its population is then prepared using its age/sex profile from the previous Census.

14 Population estimates for Local Government Areas (LGAs) that can be built from whole SA2s or SA1s are produced by aggregating the SA2- or SA1-level estimates accordingly. In Census years, where LGAs cross SA1 boundaries, Mesh Block Census counts are used to estimate the share of the SA1 population that reside in those LGAs. In post-Census years, estimates by age and sex are prepared using updated estimates of SA1 to LGAs splits, taking into account total population change implied by indicator data. Whole and partial SA1 estimates are then aggregated to LGA level.

15 The estimates in this issue are consistent with the total sub-state estimates released in the 2012-13 issue of Regional Population Growth, Australia (cat. no. 3218.0) and the state/territory estimates released in the September 2013 issue of Australian Demographic Statistics (cat. no. 3101.0). Subsequent updates to state/territory population estimates will be incorporated in the next issue of Population by Age and Sex, Regions of Australia (cat. no. 3235.0).

16 To enable the comparison of regional populations over time, historical population estimates based on consistent updated geographic boundaries are prepared. These estimates correspond with previously released estimates (on different boundaries) where possible. When official statistical boundaries, such as Local Government Areas, are updated, historical estimates are prepared based on the updated boundaries.

17 In Census years, both preliminary estimates (derived from updating ERP from the previous Census) and rebased estimates (based on the current Census) are prepared. Differences between these two sets of estimates are referred to as intercensal differences. Rebased estimates of SA2 populations for previous intercensal years are based on estimates derived by apportioning the intercensal difference evenly across the five years, while constraining the SA2 level estimates so that they sum to state/territory estimates. Rebased 2007 to 2010 estimates were derived by adding one fifth of the 2011 intercensal difference to the previous estimate of the 2007 population, two fifths to the previous estimate of the 2008 population, and so on.

18 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 should not be assumed. Percentages and estimates of change in population are based on unrounded numbers.

19 Areas with a total population of less than 1,000 people at 30 June 2008 and 30 June 2013 have been excluded from commentary in this issue.


AUSTRALIAN STATISTICAL AREAS

20 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 Local Government Areas 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 updates LGAs annually, and prepares updated and historical population estimates based on these updated boundaries.

Australian Statistical Geography Standard: Volume 1 - Main Structure and Greater Capital City Statistical Areas, July 2011 (cat. no. 1270.0.55.001)
Australian Statistical Geography Standard: Volume 3 - Non ABS Structures, July 2013 (cat. no. 1270.0.55.003)

Regional Population Growth, Australia (cat. no. 3218.0)
Australian Demographic Statistics (cat. no. 3101.0)
Australian Historical Population Statistics (cat. no. 3105.0.65.001)
Births, Australia (cat. no. 3301.0)
Deaths, Australia (cat. no. 3302.0)
Information Paper: Population Concepts (cat. no. 3107.0.55.006)
Information Paper: Population Estimates under Australia's New Statistical Geography (cat. no. 3219.0.55.001)
Population Estimates: Concepts, Sources and Methods (cat. no. 3228.0.55.001)
Regional Statistics - available on the ABS home page