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Regional population by age and sex methodology

Reference period
2020

Estimated resident population

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 is the address at which a person considers themselves to currently live. ERP includes all people who usually live in Australia (regardless of nationality, citizenship or visa status), with the exception of people present for foreign military, consular or diplomatic reasons. 

ERP, or population estimates, for Australia and it's states and territories (from now on referred to as states) are prepared quarterly and released around six months after the reference date in National, state and territory population.

Population estimates for areas below the state level (from now on referred to as sub-state) are then prepared annually. Population totals for sub-state areas are released around nine months after the 30 June reference date in Regional population. Age and sex breakdowns of these estimates are then prepared and released in this product. Estimates are prepared at the Statistical Area Level 2 and Local Government Area levels, according to the Australian Statistical Geography Standard, and are aggregated or split to create estimates for other geographies. Population estimates for Statistical Areas Levels 2 to 4, Greater Capital City Statistical Areas and Local Government Areas are available in this product.

The estimates in this product are consistent with the total sub-state estimates released on 30 March 2021 in Regional population and the state estimates by age and sex released on 18 March 2021 in the September 2020 issue of National, state and territory population. The next scheduled release of total sub-state estimates is 29 March 2022, and sub-state estimates by age and sex is 30 August 2022.

Statistics in this release are impacted by the COVID-19 pandemic and the resulting Australian Government closure of the international border from 20 March 2020.

Method

ERP as at 30 June in a Census year is calculated by adjusting Census counts of Australian usual residents to include Australian residents temporarily overseas and account for people missed or counted twice in the Census (based on the Post Enumeration Survey), and removing any births, deaths and migration movements that happened between 30 June and Census night. 

At the national and state levels, ERP is updated from the Census base every three months by taking the population estimate at the start of the quarter and adding the components of population change: natural increase (births minus deaths), net overseas migration and (in the case of state populations) net interstate migration. This is known as the component method, and uses the demographic balancing equation:

\(P_{t+1} = P_t + B - D + NOM + NIM\) where:

\(P_t\) = the estimated resident population at time point \(t\)
\(P_{t+1}\) = the estimated resident population at time point \(t+1\)
\(B\) = the number of births occurring between \(t\) and \(t+1\)
\(D\) = the number of deaths occurring between \(t\) and \(t+1\)
\(NOM\) = net overseas migration occurring between \(t\) and \(t+1\)
\(NIM\) = net interstate migration occurring between \(t\) and \(t+1\)

At the national level, net interstate migration is zero.

For Statistical Areas Level 2 (SA2s) and Local Government Areas (LGAs), population estimates are updated from the Census base annually as at 30 June also using the component method, by taking the estimate at the start of the financial year and adding natural increase (which can be negative), and net overseas and internal migration (moves between and within the states). Total estimates for each SA2 and LGA are calculated first, and then broken down by age and sex by ageing the previous year's population by one year, and incorporating the components - births (by sex), and deaths, internal and overseas migration (by age and sex). The components for sub-state areas are calculated by breaking down state-level component estimates, ensuring consistency between the state and sub-state population and component data. Components at the LGA level are constrained to those at the SA2 level to ensure consistency between these two geographies.

Once the estimates are updated, they are scrutinised and validated by ABS analysts. For areas where the components are of insufficient quality, adjustments are made. In some small areas, population change since the previous Census is assumed to be zero in the absence of reliable component data for these areas.

To provide an indication of ERP by age and sex below the SA2 level, population estimates are calculated for Statistical Areas Level 1 (SA1s). For a Census year, total SA2 estimates are apportioned across SA1s using usual residence Census counts. In intercensal years, the total SA2 estimates are apportioned across SA1s by taking into account population change implied by Medicare and electoral roll counts at the SA1 level in the years following the Census. These 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. Estimates for SA1s can be aggregated to regions such as Remoteness Areas and electoral divisions. For areas that cannot be built up from whole SA1s, such as Postal Areas and State Suburbs, mesh block Census counts are used to estimate the share of the SA1 population that resides in those areas. By these means, population estimates for areas other than those provided in this product (including SA1s) may be available on request via the ABS website.

Rebasing

After each Census, the ABS uses Census counts to construct a new base population figure for 30 June of the Census year. Rebasing is the process of updating population estimates for the five years between Censuses, to incorporate information from the most recent Census. Rebased population estimates by age and sex for each sub-state area incorporate the previous and following Census year estimates, by age cohort and sex. They are constrained to a rebased total population for each intercensal year.

Accuracy and coherence

Component data (births, deaths and overseas and internal migration) are confidentialised and constrained to add to the relevant state component estimates by age and sex. The resultant ERPs are subsequently constrained to state population estimates by age and sex. 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, all calculations are made at single year of age level. Population estimates based on single year of age may be available on request via the ABS website

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

The estimates in this product are subject to some error. Some caution should be exercised when using the estimates, especially for areas with very small populations. Areas with a total population of less than 1,000 people are excluded from commentary.

Status

To meet the competing demands for accuracy and timeliness, there are several versions of sub-state population estimates. Preliminary estimates by age and sex are available around 14 months after the reference date with revised estimates 12 months later. Rebased and final estimates are made available after each Census, when revisions are made to the estimates for all years in the previous intercensal period.

The status of annual sub-state ERP and components changes over time, from preliminary to revised to final, as new component data becomes available at the state level. With each release, ERP for the previous year only is revised due to revisions to the component data at the state level. The estimates in this product are final for 2001 to 2016, revised for 2017 to 2019, and preliminary for 2020. 

More information on the method, accuracy and status of these estimates is contained in Regional population, methodology

Components of population change

Births and deaths

Natural increase (births minus deaths) for sub-state areas is calculated using information provided by each state/territory registry of births, deaths and marriages. The data is coded based on the place of usual residence of the mother for births, and the place of usual residence of the deceased for deaths. It is aggregated to SA2 and LGA levels and constrained to published state estimates of births and deaths.

The estimates of births (by sex) and deaths (by age and sex) in this product are prepared for financial years to correspond with the 30 June reference date for sub-state ERP. To produce timely sub-state estimates, preliminary births and deaths data are prepared using year of registration as a proxy for year of occurrence.

Preliminary births and deaths are prepared by breaking down preliminary state-level data. Later, when the state-level data is updated, the sub-state data is updated accordingly and released in the next issue of this product. 

The sub-state births and deaths data in this product is not coherent with the sub-state data released in Births, Australia and Deaths, Australia which is for calendar years and has a different scope.

Overseas migration

The movement of people from overseas to Australia's sub-state areas and vice-versa cannot be directly measured and is estimated by breaking down overseas migrant arrivals and departures, by age and sex, at the state level to sub-state areas using information from the most recent Census. The state-level overseas migration data is sourced from Department of Home Affairs processing systems, visa information, and incoming passenger cards, and is published in National, state and territory population.

Regional overseas migration estimate (ROME) arrivals are estimated based on counts of people who identified in the Census that they were living overseas one year ago, at SA2 level. This distribution is used to break down state arrivals each year up until the next Census. To account for changes to the distribution of overseas arrivals within a state between Censuses (e.g. in high growth areas or inner-city areas with changing numbers of temporary migrants), adjustments may be made based on up-to-date indicator data including counts of Temporary Skills Shortage visa holders and overseas students. 

For ROME departures, a model distributes state-level overseas migrant departures to SA2s. This model is based on a range of information from the Census - mainly the number of people who arrived in each area from overseas in the last year. More weighting is given to areas that have high SEIFA Index of Education and Occupation scores and more than 20% of their total population born overseas. Of all the models evaluated, this model was selected as it best estimated population change between the last two Censuses. As with overseas arrivals, overseas departures may be adjusted based on additional information sources.

LGA estimates of ROME arrivals and departures by age and sex are prepared by converting from SA2-level ROME arrivals and departures, using a population-weighted correspondence.

Preliminary ROME arrivals and departures are prepared by breaking down preliminary state-level data. Later, when the state-level data is updated, the sub-state data is updated accordingly and released in the next issue of this product.

Internal migration

The movement of people between and within Australia's states and territories cannot be directly measured and is estimated using administrative data. Internal migration is estimated based on a combination of Census data (usual address one year ago), Medicare change of address data (provided by Services Australia), and Department of Defence records (for military personnel only), by age and sex. 

Medicare is Australia's universal health insurance scheme and covers the vast majority of Australian residents. De-identified Medicare change of address counts by age and sex are aggregated to SA2 and LGA levels. There are some people who are part of ERP but are not covered by Medicare, such as certain temporary visa holders. For others there is a time delay from when they move residence to when they update their address details with Medicare. To account for these issues, factors are applied to calibrate this data to internal migration data from the Census. These factors are applied by age, sex, state and move type (arrival or departure). Medicare data received for the year ending 30 September is used to estimate internal migration for the year ending 30 June. This assumes that on average the time between a person changing residence and registering their change of address with Medicare is three months. 

As many defence force personnel do not interact with Medicare, defence movements data is used to supplement the Medicare data. Aggregated defence force personnel movements by age and sex are converted from postcode to SA2 and LGA levels. This data reflects the time of move, and is therefore not lagged.

The Medicare and defence data are combined to prepare regional internal migration estimates (RIME) at SA2 and LGA levels. Interstate RIME moves are constrained to estimates of interstate migration by age and sex as published in National, state and territory population.

Statistical geography

The Australian Statistical Geography Standard (ASGS) brings together in one framework all of the regions which the ABS and many other organisations use to collect, release and analyse geographically classified statistics. The ASGS classification structures are split into two broad groups, ABS Structures and Non-ABS Structures.

The ABS Structures are defined and maintained by the ABS, and remain unchanged for the five years between Censuses. Further information on the ABS Structures for which population estimates are available in this product is contained in Australian Statistical Geography Standard: Volume 1 - Main Structure and Greater Capital City Statistical Areas, July 2016

The Non-ABS Structures, including Local Government Areas (LGAs), are not defined or maintained by the ABS, and generally represent administrative regions. As the Non-ABS Structures represent regions that are subject to ongoing change, the ABS releases updates to these Structures each year where significant change has occurred. Further information on the LGAs for which population estimates are available in this product is contained in Australian Statistical Geography Standard: Volume 3 - Non ABS Structures, June 2020. When boundaries for Non-ABS Structures such as LGAs change, historical population estimates for these new boundaries are prepared to enable the comparison of regional populations over time.

Maps of the statistical areas defined in the ASGS are available in the online mapping tool ABS Maps.

The population of the Other Territories, namely Christmas Island, Cocos (Keeling) Islands, Jervis Bay and Norfolk Island, is included in all references to the total population of Australia. However, the Other Territories are excluded from the commentary in this product.

Other population measures

Population pyramid graphs

Population pyramids illustrate the age and sex distribution of a population. In this product, five-year age groups are represented on the vertical axis of the graph. The population in each age-sex group is expressed as a percentage of the total population in that area. Thus, the sum of the percentages indicated by the darker bars is 100% of the population of the area represented by the darker bars, e.g. Greater Sydney. Further, the sum of the percentages indicated by the lighter bars is 100% of the area represented by the lighter bars, 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.

Confidentiality

The ABS collects statistical information under the authority of the Census and Statistics Act, 1905. This requires that statistical output shall not be published or disseminated in a manner that is likely to enable the identification of a particular person or organisation.

To guard against identification or disclosure of confidential information, all small data cells in this product are confidentialised. Any cells of under three people should be regarded as synthetic and only exist to ensure additivity to higher levels.

ABS statistics 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.

Glossary

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12/16 month rule

Under a '12/16 month rule', incoming overseas travellers (who are not currently counted in the population) must be resident in Australia for a total period of 12 months or more, during the 16 month follow-up period to then be added to the estimated resident population. Similarly, those travellers departing Australia (who are currently counted in the population) must be absent from Australia for a total of 12 months or more during the 16 month follow-up period to then be subtracted from the estimated resident population.

The 12/16 month rule does not have to be continuous and takes account of those persons who may have left Australia briefly and returned, while still being resident for 12 months out of 16. Similarly, it takes account of Australians who live most of the time overseas but periodically return to Australia for short periods.

Australian Statistical Geography Standard (ASGS)

The ASGS brings all the regions for which the ABS publishes statistics within the one framework and has been in use for the collection and dissemination of geographically classified statistics since 1 July 2011. It is the current framework for understanding and interpreting the geographical context of statistics published by the ABS.

Birth

The delivery of a child, irrespective of the duration of pregnancy, who, after being born, breathes or shows any other evidence of life such as heartbeat.

Capital city

Refers to the Greater Capital City Statistical Areas of states and territories as defined in the Australian Statistical Geography Standard.

Census

The complete enumeration of a specific population at a point in time (as opposed to a survey, which enumerates a sample of the population). When the word is capitalised, "Census" refers to the national Census of Population and Housing. The Census is run by the ABS every five years and aims to count every person in Australia on Census night.

Death

The permanent disappearance of all evidence of life after birth has taken place. The definition excludes deaths prior to live birth. For the purposes of death registration collections compiled by the ABS, a death refers to any death which occurs in, or en route to Australia and is registered with a state or territory Registry of Births, Deaths and Marriages.

Estimated resident population (ERP)

The official measure of the population of Australia, based on the concept of usual residence. It refers to all people, regardless of nationality, citizenship or legal status, 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 over a 16-month period. It excludes overseas visitors who are in Australia for less than 12 months over a 16-month period. Sub-state estimates of the resident population are prepared on an annual basis by adding natural increase (the excess of births over deaths), net overseas migration and net internal migration occurring during the period to the population at the beginning of each period.

Greater Capital City Statistical Area (GCCSA)

Represents the socioeconomic area of each of the eight state and territory capital cities. These boundaries are built from aggregations of whole Statistical Areas Level 4. GCCSA boundaries represent a broad socioeconomic definition of each capital city, containing not only the urban area of the capital city, but also surrounding and non-urban areas where much of the population has strong links to the capital city, for example through commuting to work.

Intercensal difference

The difference between two estimates at 30 June of a Census year population: the first based on the latest Census, and the second arrived at by updating the 30 June estimate of the previous Census year with intercensal components of population change.

Internal migration

The movement of people across a specified boundary within Australia involving a change in place of usual residence. Net internal migration is the number of arrivals minus the number of departures and can be either positive or negative.

Interstate migration

The movement of people over a state or territory boundary involving a change in place of usual residence. Net interstate migration is the difference between arrivals and departures and can be either positive or negative.

Local Government Area (LGA)

An ABS approximation of an officially gazetted LGA 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 major areas of Australia not administered by incorporated bodies are the northern parts of South Australia and all of the Australian Capital Territory and the Other Territories. These regions are identified as 'Unincorporated' in the LGA structure of the Australian Statistical Geography Standard.

Median age

The age at which half the population is older and half is younger.

Mesh Block

The smallest geographic region in the Australian Statistical Geography Standard (ASGS) which forms the basis for all larger regions of the ASGS. They broadly identify land use such as residential, commercial, agricultural and parks. There are approximately 358,000 Mesh Blocks and they cover the whole of Australia without gaps or overlaps.

Natural increase

The number of births minus the number of deaths.

Net overseas migration (NOM)

The net gain or loss of population through immigration to Australia and emigration from Australia.

Net undercount

The difference between the actual Census count (including imputations) and an estimate of the number of people who should have been counted in the Census. This estimate is based on the Post Enumeration Survey (PES) conducted after each Census. For a category of person (e.g. based on age, sex and state of usual residence), net undercount is the result of Census undercount, overcount, differences in classification between the PES and Census, and imputation error.

Overseas migrant arrivals

Incoming international travellers who stay in Australia for 12 months or more over a 16-month period, who are not currently counted within the population, and are then added to the population.

Overseas migrant departures

Outgoing international travellers who leave Australia for 12 months or more over a 16-month period, who are currently counted within the population, and are then subtracted from the population.

Post Enumeration Survey (PES)

The Census Post Enumeration Survey (PES) is a household survey conducted following the Census. The PES allows the ABS to estimate the number of people missed in the Census and the number counted more than once or in error. Historically more people are missed than are counted more than once in Australia, leading to a net undercount. PES estimates of net undercount are used to adjust Census counts for use in ERP.

Rebasing

After each Census, the ABS uses Census counts (adjusted for undercount) to construct a new base population figure for 30 June of the Census year. Rebasing is the process of updating population estimates for the five years between Censuses, to incorporate information from the most recent Census.

Regional internal migration estimates (RIME)

Estimates of internal migration for Australia's sub-state areas, prepared primarily using Medicare change of address information.

Regional overseas migration estimates (ROME)

Estimates of overseas migration for Australia's sub-state areas, prepared by breaking down state/territory overseas migrant arrivals and departures primarily using Census information.

Rest of state

Within each state and the Northern Territory, the area not defined as being part of the Greater Capital City is represented by a Rest of State region. The Australian Capital Territory does not have a Rest of State region.

Sex ratio

The number of males per 100 females in a population.

Statistical Area Level 1 (SA1)

An area defined in the Australian Statistical Geography Standard (ASGS) designed as the smallest unit for the release of Census data. They generally have a population of 200 to 800 people, and an average population of about 400 people. SA1s in remote and regional areas generally have smaller populations than those in urban areas. SA1s are used as the building blocks for a number of ASGS defined regions including the Section of State, Urban Centre and Localities and Remoteness Structures. SA1s are also used to approximate a number of administrative regions such as Commonwealth and State Electoral Divisions. There are approximately 57,500 SA1s and they cover the whole of Australia without gaps or overlaps. Population estimates are prepared for SA1s by breaking down estimates from the SA2 level.

Statistical Area Level 2 (SA2)

A medium-sized general purpose area defined in the Australian Statistical Geography Standard built from whole SA1s. Their purpose is to represent a community that interacts 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. SA2s generally have a population range of 3,000 to 25,000 people, and an average population of about 10,000 people. There are approximately 2,300 SA2s and they cover the whole of Australia without gaps or overlaps. SA2s are the base unit for preparing sub-state population estimates.

Statistical Area Level 3 (SA3)

An area defined in the Australian Statistical Geography Standard built up from SA2s to provide a regional breakdown of Australia. SA3s aim to create a standard framework for the analysis of ABS data at the regional level through clustering groups of whole SA2s that have similar regional characteristics. Their boundaries reflect a combination of widely recognised informal regions as well as existing administrative regions such as State Government Regions in rural areas and Local Government Areas in urban areas. SA3s generally range in population from 30,000 to 130,000 people. There are around 360 SA3s and they cover the whole of Australia without gaps or overlaps.

Statistical Area Level 4 (SA4)

An area defined in the Australian Statistical Geography Standard designed for the output of labour force data and to reflect labour markets. In rural areas SA4s generally represent aggregations of multiple 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. SA4s are built from whole SA3s. They generally have a population of over 100,000 people to enable accurate labour force survey data to be generated. There are 107 SA4s and they cover the whole of Australia without gaps or overlaps.

​​​​​​​Usual residence

Within Australia, usual residence is the address of the dwelling at which a person considers themselves to currently live, either having lived there for some time or intending to live there for some time.

Abbreviations

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AArea
ABSAustralian Bureau of Statistics
ACAboriginal Council
ACTAustralian Capital Territory
ASGSAustralian Statistical Geography Standard
BBorough
CCity
CensusCensus of Population and Housing
DCDistrict Council
ERPestimated resident population
GCCSAGreater Capital City Statistical Area
LGALocal Government Area
MMunicipality/Municipal Council
no.number
NOMnet overseas migration
NSWNew South Wales
NTNorthern Territory
PESCensus Post Enumeration Survey
QldQueensland
RRegional Council
RCRural City
RegCRegional Council
RIMEregional internal migration estimates
ROMEregional overseas migration estimates
SShire
S/Tstate or territory
SASouth Australia
SA1Statistical Area Level 1
SA2Statistical Area Level 2
SA3Statistical Area Level 3
SA4Statistical Area Level 4
TTown
Tas.Tasmania
Vic.Victoria
WAWestern Australia