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

Latest release
Reference period
2011 to 2031

Overview

Scope

The scope of the estimates and projections:

  • includes all people who usually live in Australia (regardless of nationality, citizenship or visa status)
  • excludes people present for foreign consular or diplomatic reasons.

Geography

The data available includes estimates and projections for:

  • Australia
  • States and territories
  • Remoteness Areas
  • Indigenous Regions (IREG).

Source

Estimates and projections are based on:

  • Census of Population and Housing
  • Post Enumeration Survey (PES)
  • State and territory registrars of births, deaths and marriages.

Collection method

Data used to derive the estimates and projections are collected from:

  • Paper and online forms
  • Administrative data
  • Personal interview.

Concepts, sources and methods

Descriptions of the underlying concepts and methods used are available in the Method section of Estimates and Projections, Australian Aboriginal and Torres Strait Islander population methodology.

Data sources

Overview

This release contains annual estimates and projections of the Aboriginal and Torres Strait Islander population of Australia from 30 June 2011 to 30 June 2021 and 30 June 2022 to 30 June 2031 respectively, based on results of the 2021 Census of Population and Housing.

The ABS publishes population estimates and projections following each 5-yearly Census.

These estimates and projections supersede the 2016-based series published in Estimates and Projections, Australian Aboriginal and Torres Strait Islander population methodology, 2006 - 2031 on 11 July 2019.

Scope

The scope of the Aboriginal and Torres Strait Islander population estimates and projections includes all people who usually live in Australia (regardless of nationality, citizenship or visa status), with the exception of people present for foreign consular or diplomatic reasons.

Collection

Estimates and projections of the Aboriginal and Torres Strait islander population are based on the 2021 Census of Population and Housing, Post Enumeration Survey (PES) and other demographic information. 

Demographic assumptions

Non-demographic assumptions

Coverage

These data cover Australia and its states and territories, Remoteness Areas and Indigenous Regions, as defined by the Australian Statistical Geography Standard (ASGS) Edition 3.

The category, ‘Other Territories’ is included in the Australia total, and includes Christmas Island, the Cocos (Keeling) Islands, Jervis Bay Territory and Norfolk Island.

Method

There are many techniques which may be used for population projections, such as simple extrapolations, probabilistic methods, broad economic, social and time-series analysis, account based, and detailed component methods.

Data quality issues relating to Census counts, births, deaths and migration of Aboriginal and Torres Strait Islander peoples do not support the direct component-based approach to population estimation. An indirect method is therefore required to enable the construction of a time series of the size and structure of the Aboriginal and Torres Strait Islander population.

Estimates of the Aboriginal and Torres Strait Islander population are available for 30 June of the latest Census year (currently, 30 June 2021). Based on these, backcast estimates (for previous years) and projections (for future years) can be derived using assumptions about past and future components of population change.

Due to variability in Census counts of Aboriginal and Torres Strait Islander people over time, estimates backcast from the 30 June 2021 data provide a time series based on consistent identification, unlike Census year estimates derived from previous censuses. The estimates and projections in this release therefore supersede previously published ABS estimates and projections of the Aboriginal and Torres Strait Islander population.

Three series of projections (high, medium and low series) using only demographic assumptions and one series (identification change series with medium assumptions) using demographic and non-demographic assumptions feature in the commentary. The full range of series are available in the Data Explorer datasets section of Estimates and Projections, Australian Aboriginal and Torres Strait Islander population.

Cohort-component method

The ABS uses the cohort-component method, which begins with a base population for each sex by single year of age and advances it year by year by applying assumptions regarding future fertility, mortality and migration. This procedure is repeated for each year in the projection period. Projections for each geographic region (for example, Remoteness Areas) by sex and single year of age are adjusted to sum to state or territory and Australia-level projections.

A similar technique can also be used to estimate or backcast past populations, by 'reverse-surviving' a population using mortality rates derived from life tables.

Backcast estimates

A single series of population estimates for the period 2011 to 2020 was calculated by reverse-surviving the 30 June 2021 estimated Aboriginal and Torres Strait Islander resident population using assumed life tables based on those calculated for the period 2021 to 2022. Zero net overseas migration was assumed for the period 2011 to 2021 and interstate migration levels were based on those measured in the corresponding intercensal period (that is, 2011 to 2016 and 2016 to 2021).

Method used to derive backcast estimates

Using 30 June 2021 Aboriginal and Torres Strait Islander resident population estimates as the base population, estimates were survived back 1 year at a time to 30 June 2011. For example, the number of 19-year-old males in 2020 was obtained by applying survivorship ratios from life tables to the number of 20-year-old males in 2021. This calculation is performed for all ages and both sexes to obtain the complete 2020 population and repeated to obtain estimates for each year back to 2011.

Net interstate migration assumptions have been calculated directly from the net interstate migration measured in the corresponding Census periods. As Census data indicates that the level of net overseas migration of Aboriginal and Torres Strait Islander persons is negligible, zero net overseas migration has been assumed.

For the estimates presented in this release, it was assumed that Aboriginal and Torres Strait Islander life expectancy at birth was:

Comparison to previously published estimates

Estimates and projections based on the 2021 Census are not consistent with estimates based on any other Census and should not be compared. This is due to:

For these reasons, estimates based on previous Censuses are different to those based on the 2021 Census:

  • The population estimate for 30 June 2016 based on the 2016 Census was 798,400 Aboriginal and Torres Strait Islander people. The backcast estimate for 2016 presented in this release, based on the 2021 Census, is 898,500 persons (12.5% more than the previously published 2016 estimate).
  • The population estimate for 30 June 2011 based on the 2011 Census was 669,900 Aboriginal and Torres Strait Islander people. The backcast estimate for 2011 presented in this release, based on the 2021 Census, is 806,100 persons (20.3% more than the previously published 2011 estimate).

Projections

The ABS publishes Aboriginal and Torres Strait Islander population projections after each Census. The projections are not intended as predictions or forecasts and incorporate only one non-demographic factor, that is changes to an individual’s decision to identify as being of Aboriginal and/or Torres Strait Islander origin. Other non-demographic factors which influence population change include the nature of the data collection, government policy, improvements in health treatment, access to services, and the occurrence of natural disasters. Projections are illustrations of growth and change in the structure of the Aboriginal and Torres Strait Islander population that would occur if assumptions made about future demographic and non-demographic trends held true over the projection period.

Assumptions

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.

The assumptions address one non-demographic factor (changes in whether a person identifies or is identified as being of Aboriginal and/or Torres Strait Islander origin), but 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. There is no certainty that any of the assumptions will or will not be realised. For further information on assumptions refer to the Assumptions section of Estimates and Projections, Australian Aboriginal and Torres Strait Islander population and Appendix: Identification change assumption.

Projections incorporating alternative levels and combinations of assumptions have been produced in recognition of this uncertainty and to provide a range of possible options to users (see Sensitivity to projection assumptions for more information).

Method used to derive projections

Using 30 June 2021 Aboriginal and Torres Strait Islander resident population estimates as the base population, the estimates were projected forward 1 year at a time to 30 June 2031. For example:

  • the number of 21-year-old males in 2022 was obtained by applying survivorship ratios from life tables to the number of 20-year-old males in 2021. This calculation is performed for all ages and both sexes to obtain a 'survived' population for 2022.
  • net interstate migration (by single year of age and sex) for 2022 was derived by applying migration rates to the 2021 Aboriginal and Torres Strait Islander population and adding these to the population at the relevant geography (that is, state or territory population, Remoteness Areas or Indigenous Regions).
  • to project the number of 0-year-olds in 2022, assumed age-specific fertility and paternity rates were applied to the male and female populations (respectively) aged 15 to 49 years to project total number of births for 2022. These births were then split into male and female using an assumed sex ratio at birth. Since some of these babies will die before reaching age 0, life table 'survival probability from birth age 0' was applied to project the population at age 0 for each sex separately.

The result of these steps is the projected population for 2022. This process is repeated to produce each successive year of the projection, until the year 2031.

Data release

Confidentiality

The Census and Statistics Act 1905 provides the authority for the ABS to collect statistical information and 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. This requirement means that the ABS must take care and make assurances that any statistical information about individual respondents cannot be derived from published data.

Some techniques used to guard against identification or disclosure of confidential information in statistical tables are suppression of sensitive cells, random adjustments to cells with very small values, and aggregation of data. To protect confidentiality within this release, some cell values may have been suppressed and are not available for release but included in totals where applicable. In these cases, data may not sum to totals due to the confidentialisation of individual cells.

Rounding

Population estimates and projections, and their components have sometimes been rounded. Rounded figures and unrounded figures should not be assumed to be accurate to the last digit shown. Where figures have been rounded, discrepancies may occur between sums of component items and totals.

Quality declaration

Institutional environment

Relevance

Timeliness

Accuracy

Coherence

Interpretability

Accessibility

Glossary

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Abbreviations

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Appendix: Identification change assumption

The Australian Census Longitudinal Dataset (ACLD) was used to determine the factors for the identification change assumption series, which were then applied to the medium demographic assumptions. The 2016-2021 ACLD is a representative 5 per cent sample of individuals linked across the 2016 and 2021 Censuses and includes records for 31,894 Aboriginal and Torres Strait Islander people (people whose Indigenous status was Aboriginal and/or Torres Strait Islander in 2016 and/or 2021). The ACLD contains responses to the Census Indigenous status question, so changes in identification can be quantified. The 2016-2021 ACLD sample was used for this analysis, as this is the most recent linked file and has the largest sample size.

Identification change ratios used in the identification change assumption are calculated by dividing the number of people who identified as being of Aboriginal and/or Torres Strait Islander origin on the 2021 Census by the number of people who identified as being of Aboriginal and/or Torres Strait Islander origin on the 2016 Census. The identification change ratios are calculated by age and geography.

Age groups are treated as a cohort, meaning that people aged 15 years in the 2021 Census and people aged 10 years in the 2016 Census are used when calculating the ratios. Identification change ratios for single year of age showed considerable variation, due to small sample counts in some groupings of geography by age. Therefore, age was combined into four categories (0-14 years, 15-24 years, 25-49 years, and 50 years and over) based on similar patterns of identification change within these categories.

Identification change ratios are calculated for three levels of geography: national, state/territory, and Remoteness Areas. Identification change ratios were not calculated for Indigenous Regions, due to low ACLD sample sizes in some regions.

There was not much difference in identification change between males and females, so combined identification change ratios were calculated, rather than separate ratios for each sex.

For the 2016-2021 ACLD sample (weighted to give population totals), identification change ratios by age category (0-14 years, 15-24 years, 25-49 years, and 50 years and over, as reported in the 2016 Census) and geography (national, state/territory, and Remoteness Areas, as reported for the place of usual residence in the 2021 Census) are calculated as:

\(\large{Ratio_{age_{2016},geography_{2021}} = \frac{nACLD2021_{age_{2016},geography_{2021}}}{nACLD2016_{ age_{2016},geography_{2021}}}}\)

This five-year identification change ratio is converted to an annual factor by taking the fifth root and applied as an additional assumption only in the identification change projection series. 

\(\large{AnnualFactor_{ age_{2016},geography_{2021}} = \sqrt[5]{Ratio _{ age_{2016},geography_{2021}}}}\)

Identification change ratios are calculated using ACLD sample weights, however identification change ratios calculated without weighting were also analysed and produced very similar results.

Example of including identification change assumptions as part of the projection method

Projections for each geographic region (for example, Remoteness Areas) by sex and single year of age are adjusted to sum to state or territory and Australia-level projections.

The identification change factors for each geography by age group are included in the tables below.

Identification change factor, by states and territories of usual residence in 2021, by age group in 2016
  Age group (years)
0-1415-2425-4950 and over
NSW1.051.031.041.04
Vic.1.051.031.051.04
Qld1.031.021.031.03
SA1.031.021.041.02
WA1.031.031.031.03
Tas.1.051.011.041.03
NT1.011.001.001.00
ACT1.041.031.071.01
Aust.(a)1.041.021.031.03
Identification change factor, by Remoteness Area of usual residence in 2021, by age group in 2016
  Age group (years) 
0-1415-2425-4950 and over
Major Cities of Australia1.051.031.041.04
Inner and Outer Regional Australia1.041.021.041.03
Remote and Very Remote Australia1.011.001.011.01
Australia1.041.021.031.03

History of changes

25 March 2025

  • Title of Methodology changed from 'Estimates and projections, Aboriginal and Torres Strait Islander Australians methodology, 2011 to 2031' to 'Estimates and Projections, Australian Aboriginal and Torres Strait Islander population methodology, 2011 to 2031' to bring the name in line with new guidelines as recommended by ABS's Centre of Aboriginal and Torres Strait Islander Statistics (CoATSIS).
  • Text referencing Aboriginal and Torres Strait Islander peoples has been updated in line with new guidelines.
  • To improve clarity, section titles have been updated from ‘Estimates’ to ‘Backcast estimates’ and from ‘Method used to derive estimates’ to ‘Method used to derive backcast estimates’.
  • Information on the identification change assumption has been added to the following:
  1. Section Data sources including sub-sections ‘Collection’, ‘Method’, ‘Projections’, and ‘Assumptions’
  2. Section Quality declaration including sub-section ‘Population projections’
  3. Appendix Identification change assumption
  • Editorial changes have been made to the following content:
  1. The 'Collection method' tile in section Overview
  2. Section Data sources including sub-sections ‘Scope’, ‘Collection’, ‘Method’, ‘Cohort-component method’, ‘Method used to derive backcast estimates’, ‘Comparison to previously published estimates’, ‘Projections’, and ‘Method used to derive projections’
  3. Section Data release including sub-section ‘Rounding’
  4. Section Quality declaration including sub-sections ‘Relevance’, ‘Accuracy’, (sub-sub-sections ‘Population estimates’ and ‘Population projections’), ‘Coherence’, ‘Interpretability’, and ‘Accessibility’
  5. Section Glossary.
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