### Introduction

1 This release contains annual estimates and projections of the Aboriginal and Torres Strait Islander population of Australia from 30 June 2001 to 30 June 2016 and 30 June 2017 to 30 June 2031 respectively, based on results of the 2016 Census of Population and Housing.

2 These estimates and projections supersede the 2011-based series published in Estimates and Projections, Aboriginal and Torres Strait Islander Australians, 2001 to 2026 (cat. no. 3238.0) in April 2014.

### Data quality

3 The significant volatility in the Aboriginal and Torres Strait Islander Census counts and the quality of data on births, deaths and migration of Aboriginal and Torres Strait Islander persons do not support the use of the standard approach to population estimation (observed numbers of births, deaths and migration during a specified period are added to the population at the start of the period to obtain an estimate of the population at the end of the period).

4 Data quality issues relating to Aboriginal and Torres Strait Islander population estimates for 30 June 2016 derived from the 2016 Census of Population and Housing, on which the estimates and projections in this release are based, are discussed in more detail in paragraphs 9 to 22 of the Explanatory Notes of Estimates of Aboriginal and Torres Strait Islander Australians, June 2016 (cat. no. 3238.0.55.001) and the associated Technical Note: Estimated Aboriginal and Torres Strait Islander Australian Resident Population - Method of Calculation.

5 For a discussion of the measurement of deaths of Aboriginal and Torres Strait Islander persons, see the section 'Quality issues with Aboriginal and Torres Strait Islander deaths and population data' in Life Tables for Aboriginal and Torres Strait Islander Australians (cat. no. 3302.0.55.003).

### Classifications

### Indigenous status

6 The Aboriginal and Torres Strait Islander population comprises people who are of Aboriginal origin, Torres Strait Islander origin or both Aboriginal and Torres Strait Islander origin.

The Commonwealth definition of an Aboriginal or Torres Strait Islander person is:

- of Aboriginal and/or Torres Strait Islander descent
- who identifies as being of Aboriginal and/or Torres Strait Islander origin, and
- who is accepted as such by the community with which the person associates.

7 The 2016 Census of Population and Housing (Household Form) asked the following question of each person:

## Image

### 1. Diagram: Indigenous status question on 2016 Census form.

## Description

1. Diagram: Indigenous status question on 2016 Census form.

### Australian statistical areas

8 This release contains data presented according to a number of geographic classifications: the Main Structure of the Australian Statistical Geography Standard (ASGS), the Indigenous Structure, and Remoteness Areas (RAs).

9 For further information see:

- Australian Statistical Geography Standard (ASGS): Volume 1 - Main Structure and Greater Capital City Statistical Areas, July 2016 (cat. no. 1270.0.55.001)
- Australian Statistical Geography Standard (ASGS): Volume 2 - Indigenous Structure, July 2016 (cat. no. 1270.0.55.002)
- Australian Statistical Geography Standard (ASGS): Volume 5 - Remoteness Structure, July 2016 (cat. no. 1270.0.55.005).

### Age groups

10 Estimates and projections in this release are presented by five-year age groups, with upper age groups as follows:

- Australia, states and territories - 85 years and over (65 years and over for Tasmania and the Australian Capital Territory)
- Indigenous Regions - 65 years and over
- Remoteness Areas - 75 years and over

11 Estimates and projections in this release are also presented by single year of age, with upper age groups as follows:

- Australia, states and territories - 65 years and over
- Remoteness Areas - 65 years and over

12 It is important to recognise the inherent uncertainties in these data. Aboriginal and Torres Strait Islander population estimates for 30 June 2016, on which the estimates and projections in this release are based, may be subject to errors that cannot be comprehensively adjusted for in the population estimates compilation process. This is due to the inability of the Post Enumeration Survey to adjust for net undercount by Indigenous status by single year of age and sex. Features present in single year of age Census counts may be likely to appear in population estimates for 2016, even after adjustment for net undercount and other factors have been applied, and therefore may appear in single year of age estimates for earlier years as well as projections.

13 An age heaping adjustment was applied to the population of the Northern Territory, as part of compiling the final 30 June 2016 ERP based on the 2016 Census. This information was released in Estimates of Aboriginal and Torres Strait Islander Australians, June 2016 (cat. no. 3238.0.55.001) and has been used as the base population for the estimates and projections in this release.

14 In addition, the use of assumptions on future levels of fertility, mortality and migration to obtain population projections adds a further level of uncertainty, the extent of which cannot be measured.

### Methods

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

16 As mentioned above (see paragraphs 3-5), data quality issues relating to Census counts, births, deaths and migration of Aboriginal and Torres Strait Islander persons do not support the standard approach to population estimation. An alternative 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.

17 Estimates of the Aboriginal and Torres Strait Islander population are available for 30 June of the latest Census year (currently, 30 June 2016). Based on these, estimates (for previous years) and projections (for future years) can be derived using assumptions about past and future components of population change.

18 Due to volatility in Aboriginal and Torres Strait Islander Census counts, estimates for previous years derived from the 30 June 2016 data provide a consistent time series compared to 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. See paragraphs 25-27 for a comparison of population estimates based on the 2011, 2006, and 2001 censuses.

### Cohort-component method

19 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 years of age are adjusted to sum to state or territory projections which are in turn adjusted to sum to Australia-level projections.

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

### Estimates

21 A single series of population estimates for the period 2001 to 2015 was calculated by reverse-surviving the 30 June 2016 estimated Aboriginal and Torres Strait Islander resident population using assumed life tables based on those calculated for the period 2015-2017. Zero net overseas migration was assumed for the period 2001 to 2016 and interstate migration levels were based on those measured in the corresponding intercensal period (i.e. 2001-2006, 2006-2011 and 2011-2016).

### Method used to derive estimates

22 Using 30 June 2016 Aboriginal and Torres Strait Islander resident population estimates as the base population, estimates were survived back one year at a time to 30 June 2001. For example, the number of 19-year old males in 2015 was obtained by applying survivorship ratios from life tables to the number of 20-year old males in 2016. This calculation is performed for all ages and both sexes to obtain the complete 2015 population, and repeated to obtain estimates for each year back to 2001.

23 Net interstate migration assumptions have been calculated directly from the net 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.

24 For the estimates presented in this release, it was assumed that Aboriginal and Torres Strait Islander life expectancy at birth at the Australia level increased by 0.20 years per year for males and 0.15 years per year for females for the period 30 June 2001 to 30 June 2006 and then increased by 0.30 years per year for males and 0.20 years per year for females for the 2006-2011 period. For 2011- 2016, life expectancy at birth increased by 0.40 years per year for males and 0.25 years per year for females. Whether Aboriginal and Torres Strait Islander life expectancy at birth has changed at a faster or slower rate is unknown.

### Comparison to previously published estimates

25 The estimate for 30 June 2011 based on the 2011 Census was 669,900 Aboriginal and Torres Strait Islander persons. The estimate for 2011 presented in this release, based on the 2016 Census, is 720,100 persons (7.5% more than the previously published 2011 estimate).

26 The estimate for 30 June 2006 based on the 2006 Census was 517,000 Aboriginal and Torres Strait Islander persons. The estimate for 2006 presented in this release, based on the 2016 Census, is 640,000 persons (23.8% more than the previously published 2006 estimate).

27 The total Aboriginal and Torres Strait Islander population of Australia at 30 June 2001, based on the 2001 Census, was 458,500 persons. The estimate for 2001 presented in this release, based on the 2016 Census, is 565,200 persons ( 23.3% more than the previously published 2001 estimate).

### Projections

28 The ABS publishes Aboriginal and Torres Strait Islander population projections once every intercensal period. The projections are not intended as predictions or forecasts, but 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 trends were to prevail over the projection period.

### Assumptions

29 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.

30 The assumptions do not attempt to allow for 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. Detailed information on the assumptions is described on the page: Assumptions.

31 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 the page: Sensitivity to Projection Assumptions for more information).

### Method used to derive projections

32 Using 30 June 2016 Aboriginal and Torres Strait Islander resident population estimates as the base population, the estimates were projected forward one year at a time to 30 June 2031. For example:

- the number of 21 year-old males in 2017 was obtained by applying survivorship ratios from life tables to the number of 20 year-old males in 2016. This calculation is performed for all ages and both sexes to obtain a 'survived' population for 2017;
- net interstate migration (by single year of age and sex) for 2017 was derived by applying migration rates to the 2016 Aboriginal and Torres Strait Islander population and adding these to the population at the relevant geography (that is, state or territory population, Remoteness Area or Indigenous Region); and,
- to project the number of 0 year-olds in 2017, assumed age-specific fertility and paternity rates were applied to the male and female populations (respectively) aged 15-49 years to project total number of births for 2017. These births were then split into males and females using an assumed sex ratio at birth. Since some of these births will die before reaching age 0, life table 'survival probability from birth age 0' was finally applied to project the population at age 0 for each sex separately.

33 The result of these steps is the projected population for 2017. This process is repeated to produce each successive year of the projection, until the year 2031.

### Confidentiality

34 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.

35 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

36 In this release 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.

### Acknowledgements

37 ABS publications 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.

### Additional statistics available

38 As well as the statistics included in this and related publications, the ABS may have other relevant data available on request. Inquiries should be made to the National Information and Referral Service on 1300 135 070.

39 ABS products and publications are available free of charge from the ABS web site http://www.abs.gov.au. Click on Statistics to gain access to the full range of ABS statistical and reference information.