Estimates and projections, Australian Aboriginal and Torres Strait Islander population methodology

Assumptions regarding future levels of fertility, mortality and migration are used to produce the population projections. 

The Assumptions section of Estimates and Projections, Australian Aboriginal and Torres Strait Islander population presents how the assumptions were formulated.

While the assumptions for the projections are based on an assessment of past demographic trends, both in Australia and overseas, there is no certainty that any of the assumptions will or will not be realised.

Multiple combinations of assumptions have been provided in recognition of this uncertainty and to provide users with a range of options.

There was a 25 per cent increase in Aboriginal and Torres Strait Islander people counted in the 2021 Census compared to the previous Census, and over half (56.5 per cent) of this increase was due to non-demographic change (Understanding change in counts of Aboriginal and Torres Strait Islander Australians: Census, 2021). One element of non-demographic change is people changing how they report their Indigenous status or how it is reported on their behalf. This includes whether Indigenous status is actually reported or not.

The decision around whether to identify as being of Aboriginal and/or Torres Strait Islander origin, or change from previous identification, can be informed by many personal and external factors (historical and contemporary). This can include understanding of why the information is being collected and how it will be used, cultural safety, previous exposure to discrimination or racism, stage of a persons’ life course, and whether a person is reporting on their own behalf or not.  

A new projection series has been produced to include an assumption on changes in identification. This assumption is based on information from the Australian Census Longitudinal Dataset (ACLD) on how the response to the question on Indigenous status changed between the 2016 and 2021 Census. The Indigenous status identification change assumption uses net change and has been applied to the medium demographic assumption series. 

ABS's estimates and projections of the Aboriginal and Torres Strait Islander population of Australia are based on population estimates derived from the most recent Census of Population and Housing (currently 2021) and Post Enumeration Survey, as well as data from the birth and death registration collections. Assumptions about past and future levels of the components of population change are applied to the base Census population in order to produce estimates (for earlier reference years) and projections (for future reference years).

Assumptions are derived from an analysis of data sourced from a variety of institutional environments. Much of this data is administrative by-product data collected by other organisations. Assumptions on fertility and mortality are based on births and deaths statistics extracted from registers administered by the various state and territory Registrars of Births, Deaths and Marriages.

For information on the institutional environment of the ABS, including the legislative obligations of the ABS, financing and governance arrangements, and mechanisms for scrutiny of ABS operations, please see ABS Institutional Environment.

Aboriginal and Torres Strait Islander population estimates for years prior to the base population provide estimates on a temporally consistent basis, thus eliminating any inconsistencies in estimates due to the changing propensity of people to identify, or be identified, as being of Aboriginal and/or Torres Strait Islander origin across Censuses or changes to the methods used to collect this information. Estimates are published for Australia and the states/territories, by 5-year age groups and sex. Single year of age data is also available for persons only.

Population projections inform on future changes in the Aboriginal and Torres Strait Islander population of Australia, such as population growth/decline and changes in age structure. They are used by governments, policy makers, planners, the private sector, and others for a range of purposes such as policy design, policy implementation, performance reporting, and service planning. They are commonly used to estimate future demand for products, services, infrastructure, energy, water, and funding. Aboriginal and Torres Strait Islander population projections are important for supporting national reporting on health and socio-economic wellbeing of the Aboriginal and Torres Strait Islander population. 

Projections are published for Australia, states/territories, Indigenous Regions and 3 categories of Remoteness Areas, by 5-year age groups and sex. Single year of age data is also available for Australia, states/territories and 3 categories of Remoteness Areas for persons only.

Assumptions have been formulated on the basis of past demographic trends, in conjunction with consultation with various experts and government department representatives at the national and state/territory level.

ABS's Aboriginal and Torres Strait Islander population estimates and projections are compiled and published once every 5 years (that is, after each Census of Population and Housing).

The estimates and projections presented in this release are based on results of the 2021 Census of Population and Housing, adjusted for net undercount as measured by the Post Enumeration Survey (PES). The goal of the Census is to obtain a complete measure of the number, and characteristics, of people in Australia on Census night and their dwellings.

The ABS conducts the PES shortly after the Census to determine how many people were missed (undercount) and how many were counted more than once or in error (overcount). For 2021, the net undercount of the Aboriginal and Torres Strait Islander population was 170,800 persons (17.4%), which is similar to the rate for the 2016 Census (17.5%). The extent of undercoverage of Aboriginal and Torres Strait Islander peoples in the 2021 Census, the relatively small sample size of the PES to adjust for the undercoverage, and the number of Census records with unknown Indigenous status means that 2021 population estimates, and backcast estimates and projections based on them, should be interpreted with caution. For more information see Estimates of Aboriginal and Torres Strait Islander Australians, 30 June 2021.

It is important to remember that while the Census, PES and other administrative datasets used in compiling these estimates produce statistics with relatively small amounts of error, this error can be more significant when focussing on very small populations (like the Aboriginal and Torres Strait Islander population).

Given that the quality of historical Aboriginal and Torres Strait Islander component data (births, deaths and migration) is variable, ABS's Aboriginal and Torres Strait Islander backcast population estimates for non-Census years are produced by applying assumptions about past levels of Aboriginal and Torres Strait Islander life expectancy at birth and net interstate migration to the population. As levels of life expectancy at birth are known only for Census years and any changes in the intercensal period are unknown, estimates should be treated with caution.

Aboriginal and Torres Strait Islander population estimates for 2011 to 2020 based on the 2021 Census supersede previously published estimates for this period.

ABS's Aboriginal and Torres Strait Islander population projections are based on a number of assumptions on future levels of fertility, mortality and migration. They are illustrative of growth and change in the Aboriginal and Torres Strait Islander population that would occur if the assumptions held true over the projection period.

While the assumptions are formulated on the basis of an assessment of past demographic trends and changes in individuals' propensity to identify, or be identified, as being of Aboriginal and/or Torres Strait Islander origin, there is no certainty that any of the assumptions will be realised. In addition, the assumptions do not allow for other non-demographic factors (such as major government policy decisions, economic factors, natural disasters, epidemics, or significant health treatment improvements) which may affect future demographic behaviour or outcomes.

The accuracy of each component of the data presented in this release is also affected by changing social norms and an individual's propensity to identify as being of Aboriginal and/or Torres Strait Islander origin. This propensity is not only affected by an individual's decision on how they choose to identify, but also by improvements to collection methods that allow the data to be captured more accurately. This propensity can change over time and between collections, which can significantly affect the accuracy of the data.

The estimates and projections presented in this release are not consistent with estimates and projections based on 2016 or previous Censuses. As the assumptions used in each successive set of Aboriginal and Torres Strait Islander population estimates and projections incorporate recent trends, comparison of data across issues of this release is not advised. As mentioned above, the coherence of this data is also affected by whether and how individuals are identified as being of Aboriginal and/or Torres Strait Islander origin in each collection and the ability of each dataset to accurately capture this information which can vary across time and between data sources. The coherence between the estimates and projections compiled at different points in time is explored in more detail in the article, Guide to using historical estimates for comparative analysis and reporting.

ABS's population projections are not intended as predictions or forecasts and should not be considered as such. Rather, they are illustrations of growth and change in the population that would occur if the assumptions held true over the projection period.

For more information on the method used to compile ABS's Aboriginal and Torres Strait Islander population estimates and projections refer to the Method section of Estimates and Projections, Australian Aboriginal and Torres Strait Islander population methodology and the Assumptions section of Estimates and Projections, Australian Aboriginal and Torres Strait Islander population.

Aboriginal and Torres Strait Islander population estimates and projections are available in a variety of formats on the ABS website. The main features, which includes the key estimates, commentary, data cubes (in Microsoft Excel spreadsheet format) and Data Explorer datasets, are available free on the web.

The ABS observes strict confidentiality protocols as required by the Census and Statistics Act 1905. This may restrict access to data at a very detailed level which is sought by some users.

The birth of a live-born child where either the mother or the father was identified as being of Aboriginal and/or Torres Strait Islander origin on the birth registration form.

The death of a person who is recorded as being of Aboriginal and/or Torres Strait Islander origin on the Death Registration Form (DRF). From 2007, Indigenous status for deaths registered in South Australia, Western Australia, Tasmania, the Northern Territory and the Australian Capital Territory is also derived from the Medical Certificate of Cause of Death (MCCD). If the Indigenous status reported on the DRF does not agree with that on the MCCD, an identification from either source that the deceased was of Aboriginal and/or Torres Strait Islander origin is given preference over non-Indigenous.

People who identified themselves, or were identified by another household member, as being of Aboriginal origin, Torres Strait Islander origin, or both Aboriginal and Torres Strait Islander origin.

The phenomenon of uneven population age distribution in Census or survey data. When age heaping occurs, data show systematic spikes on particular ages such as those ending in 0 or 5. This happens as a result of 'digit preference' or rounding when respondents are unsure of their age or the age of others they are reporting on behalf of.

A bar chart graphically representing the age structure of the population, usually in five-year age groups, for males and females separately. The age structure of the population usually approximates the shape of a pyramid because mortality progressively reduces the number in each birth cohort as it ages. The age pyramid is useful to show the existence of unusually large or small cohorts, and in this way, not only conveys information about a country's past demographic history, but also a great deal about its demographic future.

The number of deaths (either occurred or registered) during the calendar year at a specified age per 1,000 of the estimated resident population of the same age at the mid-point of the year (30 June). Pro rata adjustment is made with respect to deaths for which the age of the deceased is not given.

The number of live births (either occurred or registered) during the calendar year, according to the age of the mother, per 1,000 of the female estimated resident population of the same age at 30 June. In the calculation of these rates, births to mothers under 15 years are included in the 15 to 19 years age group, and births to mothers aged 50 years and over are included in the 45 to 49 years age group. Pro rata adjustment is made for births for which the age of the mother is not given.

The number of live births (either occurred or registered) during the calendar year, according to the age of the father, per 1,000 of the male estimated resident population of the same age at 30 June. In the calculation of these rates, births to fathers under 15 years are included in the 15 to 19 years age group, and births to fathers aged 50 years and over are included in the 45 to 49 years age group. Pro rata adjustment is made for births for which the age of the father is not given.

The ASGS defines all the regions for which the ABS releases statistics within the one framework and is used by the ABS for the collection and dissemination of geographically classified statistics. It is the current framework for understanding and interpreting the geographical context of statistics released by the ABS.

For more information, please refer to Main Structure and Greater Capital City Statistical Areas, Australian Statistical Geography Standard (ASGS) Edition 3.

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

A census is 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.

Completed fertility represents the average number of births a cohort of females have borne over their reproductive lifetimes.

The permanent disappearance of all evidence of life after birth has taken place. The definition excludes all deaths prior to live birth. For the purposes of the ABS Death Registration collection, 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.

The official measure of the population of Australia is 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.

Data are also presented according to the Indigenous Structure of the ASGS. Under this classification, Indigenous Regions (IREGs) are defined as:

• Indigenous Regions (IREGs): Are large geographical areas loosely based on the former Aboriginal and Torres Strait Islander Commission (ATSIC) boundaries. The greater population of IREGs enables greater cross classification of variables when compared with Indigenous Areas (IAREs) and Indigenous Locations (ILOCs). IREGs do not cross state or territory borders and are aggregates of one or more IAREs.

For more information, please refer to Indigenous Structure, Australian Statistical Geography Standard (ASGS) Edition 3.

Indigenous status indicates whether a person identifies, or is identified, as being of Aboriginal and/or Torres Strait Islander origin. Indigenous status is reported (either by an individual or a person responding to a survey or Census on their behalf) in response to the question: Is the person of Aboriginal or Torres Strait Islander origin?

The time period between 30 June in the previous Census year and 30 June of the latest Census year.

The movement of people over a state or territory boundary for the purpose of changing their place of usual residence. Net interstate migration is the number of arrivals minus the number of departures.

The average number of additional years a person of a given age and sex might expect to live if the age-specific death rates of each period continued throughout their lifetime.

Life expectancy summarises the mortality experience of a population by measuring how long, on average, a group of people born in the same year would be expected to live, if current death rates at each age remained the same. Life expectancy can be calculated for any age using life tables (a table which shows the probability of dying at each age), though life expectancy at birth is what most people focus on. Life expectancy at birth is the average number of years that a group of newborn babies would be expected to live if current death rates remain unchanged. Since death rates in the population will change during a person’s lifetime and a person may die at an earlier or later age, life expectancy is only a summary indicator for a population, rather than an exact measure of how long individuals will actually live.

A tabular, numeric representation of mortality and survivorship of a cohort of births at each age of life. The conventional life table is based on the assumption that as the cohort passes through life it experiences mortality at each age in accordance with a predetermined pattern of probabilities of dying (qx) which do not change from year to year. The life table is a hypothetical model of mortality, and even though it is usually based upon death rates from a real population during a particular period of time, it does not describe the real probabilities of dying which characterise a cohort as it ages.

Life tables may be complete or abridged, depending on the age interval used in their compilation. Complete life tables such as those for the Australian population contain data by single years of age. Abridged life tables such as those for the Aboriginal and Torres Strait Islander population contain data for five-year age groups. Due to differences in qx patterns between males and females at different ages, life tables are generally constructed separately for each sex.

For any distribution, the median value is that which divides the relevant population into two equal parts, half falling below the value, and half exceeding it. Thus, the median age is the age at which half the population is older, and half is younger.

The movement of people across a specified boundary for the purpose of establishing a new or semi-permanent residence. Migration can be international (migration between countries) and internal (migration within a country).

The difference in mortality when comparing one population group with another. In this release, it is calculated as the ratio of life expectancy at birth for a particular geographic region (for example, state/territory) over the life expectancy at birth for Australia.

The number of births minus the number of deaths.

Net interstate migration is the net gain or loss of population through interstate migration being the change of a person's place of usual residence from one state or territory to another state or territory.

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

For Australia, net population growth is the sum of natural increase and net overseas migration. For the states and territories, net population growth also includes net interstate migration.

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 was based on the Post Enumeration Survey (PES) conducted after each Census. For a category of persons (for example, based on age, sex and state/territory of usual residence), net undercount was the resultant of Census undercount, overcount and imputation error.

Following the 1992 amendments to the Acts Interpretation Act to include the Indian Ocean Territories of Christmas Island and the Cocos (Keeling) Islands as part of geographic Australia, another category at the state and territory level was created, known as Other Territories. From 1 July 2016, the Australian Government assumed responsibility for Norfolk Island. Other Territories includes Jervis Bay Territory, previously included with the Australian Capital Territory, as well as Christmas Island, the Cocos (Keeling) Islands and Norfolk Island.

A household survey conducted three to four weeks after the Census. The PES allows the ABS to estimate the number of people who should have been counted in the Census compared to the number who were. Results from the PES contribute to a more accurate calculation of the estimated resident population (ERP) for Australia and the states and territories which is then backdated to 30 June of the Census year. While the Census is self-completed, the Post Enumeration Survey is conducted via interview. This means that all survey responses are completed, including the Indigenous status of each person (that is, there are no missing or ‘not stated’ responses).

The Australian Statistical Geography Standard (ASGS) Remoteness Structure divides Australia into 5 classes of remoteness which are characterised by a measure of relative geographic access to services. The 5 Remoteness Areas (RAs) are:

• Major Cities of Australia
• Inner Regional Australia
• Outer Regional Australia
• Remote Australia
• Very Remote Australia.

Due to insufficient data for some RAs, particularly at younger ages, the ABS has produced estimates and projections for 3 categories of remoteness. These are:

• Major Cities
• Inner Regional and Outer Regional combined
• Remote and Very Remote combined.

While statistical data classed to this structure may be available by state/territory, characteristics of remoteness are determined in the context of Australia as a whole. Therefore, not all RAs are represented in all states and territories.

For more information and a map of the areas, see Australian Statistical Geography Standard (ASGS): Edition 3 - Remoteness Areas, July 2021.

The number of males per 100 females.

The sum of age-specific fertility rates for Aboriginal and Torres Strait Islander females (live births at each age of mother per 1,000 females of the estimated resident population of that age) divided by 1,000. It represents the number of children a female would bear during her lifetime if she experienced current age-specific fertility rates at each age of her reproductive life (ages 15 to 49).

The sum of age-specific paternity rates for Aboriginal and Torres Strait Islander males, where the mother's Indigenous status is non-Indigenous or not stated, expressed as a rate per man. It represents the number of children a male would father during his lifetime if he experienced current age-specific paternity rates at each age of his reproductive life.

The intercensal growth in the Aboriginal and Torres Strait Islander population that cannot be fully explained by births, deaths and migration.

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.

The usual residence of a newborn is that of the mother.