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EXPLANATORY NOTES


INTRODUCTION

1 This release 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 2017, 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 2016 and preliminary for 2017.

3 The estimates in this issue are consistent with the revised total sub-state estimates released in the 2016-17 issue of Regional Population Growth, Australia (cat. no. 3218.0) on 31 August 2018 and the state/territory estimates released in the December 2017 issue of Australian Demographic Statistics (cat. no. 3101.0). Subsequent updates to state/territory population estimates will be incorporated in the next issue of Regional Population by Age and Sex, Australia (cat. no. 3235.0), to be released in August 2019.


ESTIMATED RESIDENT POPULATION - AUSTRALIA

4 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. For the 30 June reference date, this refers to the calendar year around it.

5 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. A person is regarded as a usual resident if they have been (or expected to be) residing in Australia for a period of 12 months or more over a 16-month period.

6 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, interstate migration is also taken into account. 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.

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

Statistical Area Level 2 (SA2)

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 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 Home Affairs. As the Census is not held on 30 June (the 2016 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 consistency to the unconfidentialised ERP.

10 Since 2016, SA2 populations are updated in post-Census years by adding to the estimated population at the beginning of each period the components of natural increase (births minus deaths), net regional internal migration estimates (RIME) and net regional overseas migration estimates (ROME), by SA2. This method and its data sources are explained in Feature Article: New Methodology Used to Prepare Sub-state Population Estimates. In some very small areas, population change since the previous Census may be is assumed to be zero in the absence of reliable component data for these areas. All SA2 estimates are scrutinised and validated by ABS analysts. Local knowledge, such as that advised by state governments (including peer reviewers) is considered and 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-Census years are then broken down by age and sex. Since 2016, SA2 populations by age and sex are updated from the previous year's estimates by ageing the population by one year, and incorporating the components of population change - births (by sex), and deaths, RIME and ROME (by age and sex). Further information on the data sources used to estimate sub-state components of population change is contained in the Explanatory Notes of Regional Population Growth, Australia (cat. no. 3218.0). Prior to 2016, the internal and overseas migration components were based on migration profiles from the previous Census. For areas where the components are of insufficient quality, adjustments are made. These components are confidentialised and constrained to add to the relevant state/territory component estimates by age and sex. The resultant ERPs are subsequently constrained to add to the relevant state/territory population estimates by age and sex. Also as a result of confidentialisation 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 may be available on request as a charged consultancy.

12 While sub-state ERP by age and sex is consistent with state/territory ERP by age and sex, differences arise between aggregated sub-state components by age and otherwise published state/territory components by age. This is due to the different reference period of sub-state ERP (annual as at 30 June) and state/territory ERP (quarterly), as the age of a person at the end of the financial year can be be different to the age of that person at the end of each quarter.

13 In Census years, both preliminary estimates (derived from updating ERP from the previous Census) and rebased population 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 across the five years, while constraining the SA2 level estimates so that they sum to state/territory estimates. Rebased 2012 to 2015 estimates were generally derived by adding one-fifth of the 2016 intercensal difference to the previous estimate of the 2012 population, two-fifths to the previous estimate of the 2013 population, and so on.


Statistical Area Level 1 (SA1) and SA1-based geographies

14 The SA1 is the smallest geographic unit for the release of Census data. There are approximately 57,500 SA1s and they cover the whole of Australia without gaps or overlaps. To provide some indication of ERP below the SA2 level, the ABS prepares population estimates for SA1s. These estimates can be aggregated to form population estimates for regions such as Remoteness Areas and Electoral Divisions. By this means, population estimates for areas other than those provided in this product (including SA1s) may be available on request.

15 Population estimates at the SA1 level as at 30 June of a Census year are compiled by apportioning the population estimate for each SA2 across the SA1s within the SA2, using Census usual residence counts by age and sex. Total SA1 population estimates are updated in post-Census years using aggregated Medicare enrolments and Australian Electoral Roll counts at the SA1 level. These total SA1 populations are then broken down by age and sex by ageing the previous year's population, with age distributions for selected areas held static.


Local Government Area (LGA)

16 In Census years, LGA ERP by age and sex is aggregated from whole SA2 or SA1 level estimates by age and sex where possible. Where LGAs cross SA1 boundaries, Mesh Block Census counts are used to estimate the share of the SA1 population that reside in those LGAs. LGA population estimates by age and sex are updated in post-Census years by accounting for the components of population change. The resulting LGA ERP by age and sex is constrained to SA2 ERP by age and sex to ensure consistency between these two geographies, based on the smallest possible regions where SA2 and LGA boundaries match in terms of the combined area containing resident population. For example, where one LGA region equals one SA2 region exactly or where a group of LGAs equals a group of SA2s, the ERP by age and sex for these areas will match.

17 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.


ACCURACY OF SUB-STATE POPULATION ESTIMATES

18 In recognition of the inherent difficulty 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 2017 have been excluded from commentary in this issue.


AUSTRALIAN STATISTICAL AREAS

20 This publication contains data presented according to the 2016 edition of the Australian Statistical Geography Standard (ASGS), which refers to boundaries as defined at 1 July 2016. 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 departments. 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 2016 (cat. no. 1270.0.55.001)
Australian Statistical Geography Standard: Volume 3 - Non-ABS Structures, July 2017 (cat. no. 1270.0.55.003)

Australian Demographic Statistics (cat. no. 3101.0)
Regional Population Growth, Australia (cat. no. 3218.0)
Births, Australia (cat. no. 3301.0)
Deaths, Australia (cat. no. 3302.0)
Migration, Australia (cat. no. 3412.0)
Australian Historical Population Statistics (cat. no. 3105.0.65.001)
Information Paper: Population Concepts (cat. no. 3107.0.55.006)
Population Estimates: Concepts, Sources and Methods (cat. no. 3228.0.55.001)
Quality Assurance of Rebased Population Estimates, 2016 (cat. no. 3250.0.55.001)
Data by Region