Estimates and Projections, Aboriginal and Torres Strait Islander Australians

A single time series of Aboriginal and Torres Strait Islander estimates for the period 2006 to 2016 has been produced. 

Over this period life expectancy at birth is assumed to:

• increase by 0.40 years per year for males and 0.25 years per year for females between 2011 to 2016
• increase by 0.30 years per year for males and 0.20 years per year for females between 2006 to 2011.
   

Net interstate migration for each of the above two intercensal periods was based on levels observed in each respective intercensal period. 

Zero net overseas migration occurred across the entire series with no arrivals and departures.

Assumptions have been formulated on the basis of past demographic trends, in conjunction with consultation with various experts and government department representative at the national and state/territory level. They do not attempt to allow for non-demographic factors (such as major government policy decisions, economic factors, natural disasters, epidemic or significant health treatment improvements) which may alter future demographic behaviour or outcomes.

Additional assumptions regarding the remaining demographic factors for the projections are:

• constant interstate migration at levels observed in the 2016 Census
• zero net overseas migration with no arrivals and no departures
• zero unexplained growth in Aboriginal and Torres Strait Islander population.
   

By considering the above assumptions, nine projection series were produced. Three main series have been selected from these to provide a range of projections for analysis and discussion in this publication. These series are referred to as series A (high), series B (medium) and series C (low). Detailed information on these and the remaining projection series are available in the data cubes. 

The three main series respectively imply a high, medium and low overall growth rate of the Aboriginal and Torres Strait Islander population. It is expected that series B will be the most appropriate choice for most users. The ABS will be using series B in calculating fertility and mortality rates for inclusion in the annual Births and Deaths publications. 

The effect of alternative assumptions on the size of the future Aboriginal and Torres Strait Islander population is described in the Chapter: Sensitivity to Projection Assumptions.

The population projections are not intended as forecasts or predictions, but are illustrations of growth and change in the population that would occur if assumptions made about future demographic trends were to prevail over the projection period. Future uncertainty, along with the subjective nature of assessing current trends, means that using a range of possible outcomes rather then a single projection series acknowledges a range of the possible future size, distribution and age structure of Australia's Aboriginal and Torres Strait Islander population. 

There is also some level of uncertainty surrounding 2016 Aboriginal and Torres Strait Islander Census counts and population estimates on which the projections are based, as well as data quality issues relating to registered births and deaths of Aboriginal and Torres Strait Islander people. Information on data quality issues related to Aboriginal and Torres Strait Islander estimates and projections are available in the Quality Declaration. 

The ABS Births collection identifies a birth as being an Aboriginal and/or Torres Strait Islander person where at least one parent identifies themselves as being of Aboriginal and Torres Strait Islander origin on the birth registration. These can be attributed to either:

• Aboriginal and Torres Strait Islander mothers, including births where both the mother and father are Aboriginal and Torres Strait Islander
• Aboriginal and Torres Strait Islander fathers and non-Indigenous mothers.
   

For simplicity, birth rates of Aboriginal and Torres Strait Islander mothers are referred to in this release as fertility rates, while birth rates where the father is Aboriginal and Torres Strait Islander and the mother's Indigenous status is non-Indigenous or not stated are referred to as paternity rates.

To produce population projections using the cohort-component method, assumptions for each year of the projection period are required for age-specific fertility rates, age-specific paternity rates and the Aboriginal and Torres Strait Islander sex ratio at birth.

Of the Aboriginal and Torres Strait Islander births registered in 2017:

• 27% were births for which both parents identified themselves as being of Aboriginal and Torres Strait Islander origin on the birth certificate statement
• 43% were births where only the mother was of Aboriginal and Torres Strait Islander origin (including births where paternity was not acknowledged or the father's Indigenous status was not stated)
• 30% were births where only the father was of Aboriginal and Torres Strait Islander origin (including births where the mother's Indigenous status was not stated).
   

The proportion of Aboriginal and Torres Strait Islander births attributed to Aboriginal and Torres Strait Islander mothers and/or Aboriginal and Torres Strait Islander fathers differs considerably between the states and territories. 

In 2017:

• The Northern Territory had the highest proportion of births (43%) where both the mother and father were Aboriginal and Torres Strait Islander
• Tasmania had the lowest proportion of births (12%) where both mother and father were Aboriginal and Torres Strait Islander
• 39% of births in the Australian Capital Territory were to non-Indigenous mothers and Aboriginal and Torres Strait Islander fathers (11% in the Northern Territory).
   

Population projections require an assumed sex ratio at birth in order to split total projected births into male and female births. The sex ratio for Aboriginal and Torres Strait Islander births registered in Australia fluctuates around 103 to 109 male births per 100 female births. A constant ratio of 105.6 males per 100 female births has been assumed for the duration of the projection period.

Three main assumptions have been made for future fertility rates of Aboriginal and Torres Strait Islander women:

• Constant fertility rates at the 2017 level
• An annual decline of 1.0% in fertility rates
• An annual decline of 1.5% in fertility rates.
   

These assumptions were primarily chosen on the basis of the declining trend in fertility as indicated by data from the 'children ever born' question asked in the Census. 

The same rate of decline in fertility rates have been assumed for each state and territory, Indigenous Regions and Remoteness Area.

Cohort fertility rates, based on the 'children ever born' question asked in the Census illustrate a decline in Aboriginal and Torres Strait Islander fertility over time. 

The number of children ever born provides information on actual fertility outcomes of women of different ages. In particular, the number of children ever born to women aged 40-44 year can be regarded as a measure of completed fertility; that is, on average how many children this group of women each had throughout their entire reproductive lifetimes. 

Aboriginal and Torres Strait Islander women aged 40-44 years had on average:

• 3.97 babies per woman in the 1986 Census
• 3.10 babies per woman in he 1996 Census
• 2.84 babies per woman in the 2006 Census
• 2.82 babies per woman in the 2011 Census
• 2.77 babies per woman in the 2016 Census
   

The average number of children ever born to Aboriginal and Torres Strait Islander women has been declining for each age group over the past three decades. These declines, particularly in the younger age groups, indicate probable declines in the future overall level of Aboriginal and Torres Strait Islander fertility.

The total fertility rate (TFR), based on birth registrations, represents the average number of children a woman could expect to bear during her lifetime if she experienced current age-specific fertility rates at each age of her reproductive life. 

The TFR for Aboriginal and Torres Strait Islander women:

• Was 1.9 babies per woman in 2001
• Gradually increased to 2.5 in 2010, before slowly decreasing over the period 2012 to 2016
• By 2017, increased to 2.3 babies per woman.
   

In summary, while fertility rates based on birth registrations of Aboriginal and Torres Strait Islander children may provide some evidence for assuming constant or increasing Aboriginal and Torres Strait Islander fertility, cohort fertility rates based on the 'children ever born' question asked in the Census indicate long-term declines. Assumptions that take both sets of evidence into account have been made but with more emphasis given to the 'children ever born' data.

• Low series: The magnitude and duration of any future changes in fertility rates are not possible to gauge accurately, but it's possible that a decline observed between 2012 to 2016 may continue during the projection period. On this basis, low series assumes an annual decline of 1.5%.
• Medium series: assumes an annual decline of 1% which is equivalent to the decline in average children per Aboriginal and Torres Strait Islander woman in the last ten years.
• High series: assumes constant fertility rate as observed in 2017.
   

Assumed age-specific fertility rates for Aboriginal and Torres Strait Islander women are based on three years of birth registrations (2015 to 2017) in order to minimise the effect of year-to-year fluctuations in registrations. These rates were adjusted to produce plausible numbers of projected births in the first year of the projection period in accordance with Aboriginal and Torres Strait Islander population estimates at younger ages.

Adjustment factors were calculated for each state and territory by taking the ratio of the number of Aboriginal and Torres Strait Islander children aged 0, 1 and 2 at 30 June 2016 to the number of births registered between 2015 and 2017. Differences in the two sources can be attributed to several factors, including:

• net undercount
• Census records for which Indigenous status was not stated
• lags in the registration of births
• differences in the method of identification between the Census and the Birth registration collection (for example, identified as Aboriginal and Torres Strait Islander in the birth registration but not on the Census form).
   

As rates are required on a financial year basis they were adjusted to account for the six-month period between the mid-point of the period 2015–17 (calendar year fertility rates) and 2016–17 (financial year fertility rates).

Assumed declines in fertility rates are applied uniformly across relevant age groups.

The projections in this release apply fertility assumptions for sub-state geographies by aggregating Indigenous Regions (IREGs) into two groups for each state and territory (except Tasmania and the Australian Capital Territory):

• capital city IREG (for example, Adelaide IREG)
• rest of state/territory IREGs combined (for example, Port Augusta IREG and Port Lincoln - Ceduna IREG combined).
• Fertility rates for each of these groups were adjusted in a similar manner to state and territory rates to produce plausible numbers of projected births in the first year of the projection period in accordance with Aboriginal and Torres Strait Islander population estimates at younger ages.
   

Assumed fertility rates for Remoteness Areas were calculated and adjusted using the same technique as for the states and territories.

The total paternity rate (TPR) is defined as the average number of Aboriginal and Torres Strait Islander babies born per Aboriginal and Torres Strait Islander father where the mother's Indigenous status is non-Indigenous or not stated, and is calculated in the same way as the TFR.

Three main assumptions have been made for future paternity rates:

• constant paternity rates
• an annual increase of 1.0% in paternity rates
• an annual increase of 2.0% in paternity rates.
   

The same rate of increase in paternity rates has been assumed for each state and territory, Indigenous Region, and Remoteness Area.

As with the TFR, the time series of the TPR is based on population estimates which are not strictly comparable over time. Based on birth registrations, the TPR has been slowly increasing over more than a decade, from 0.77 births per Aboriginal and Torres Strait Islander male in 2001 to 1.06 in 2017.

The 'children ever born' question is not asked of males in the Census. Therefore, there is no reliable source other than birth registrations for calculating paternity rate.

• Low series: assumes constant paternity rate over the projection period.
• Medium series: paternity rate calculated from birth registration data has been slowly increasing over time and showed an increase of 1.1% during 2006 to 2016. To reflect this trend, medium series assumes an annual increase of 1% in paternity rate.
• High series: the increase in paternity rate in the recent years might have been underestimated due to registration lags. Therefore, an annual increase in paternity rate of 2% is assumed for high series.
   

Assumed age-specific paternity rates for Aboriginal and Torres Strait Islander men are based on three years of birth registrations (2015 to 2017) where the mother's Indigenous status is non-Indigenous or not stated, which were then adjusted to ensure consistency with the Aboriginal and Torres Strait Islander population at younger ages. Assumed increases in paternity rates are applied uniformly across relevant age groups.

Assumed paternity rates for IREGs were calculated and adjusted using the same technique as for the states and territories.

Assumed paternity rates for Remoteness Areas were calculated and adjusted using the same technique as for the states and territories.

To produce population projections using the cohort-component method, life tables are required for each year of the projection period. These are calculated in two steps:

• life expectancy at birth for each projection year is assumed
• life tables, based on the 2015 to 2017 age/sex structure of mortality, are generated to match the assumed life expectancies at birth.
   

Survivorship ratios from the life tables are then applied to the population by single year of age and sex.

Assumptions for mortality at lower geographical levels are based on 2015 to 2017 differentials between Australia and each state or territory, groups of Indigenous Regions, and Remoteness Areas.

At the national level, Aboriginal and Torres Strait Islander life expectancy at birth for the period 2015 to 2017 is estimated to be 71.6 years for males and 75.6 years for females (see Life Tables for Aboriginal and Torres Strait Islander Australians, 2015–2017).

As survivorship ratios are required on a financial year basis, life expectancy at birth estimates are adjusted to account for the six-month period between the midpoint of 2015–17 (calendar year life expectancy) and 2015–16 (financial year life expectancy), resulting in life expectancy at birth of:

• 71.4 years for Aboriginal and Torres Strait Islander males
• 75.5 years for Aboriginal and Torres Strait Islander females.
   

The ABS has compiled life tables for Aboriginal and Torres Strait Islander Australians after each Census since 1996. Due to changes in the methods, the 2006, 2011 and 2016 estimates of life expectancy at birth are not comparable to estimates for earlier periods. Assumptions about future levels of Aboriginal and Torres Strait Islander life expectancy at birth can therefore only be based on observed trends over the two most recent intercensal periods. 

A study (Wilson, Condon and Barnes, 2007) found evidence that in the Northern Territory:

• life expectancy at birth increased from 52 years for males and 54 years for females in the 1960's, to 60 years and 68 years respectively in recent years
• improvements in infant mortality contributed to increases in life expectancy at birth between the late 1960's and early 1980's
• Since then, life expectancy gains have been largely the result of improving mortality of people aged 45 years and over.
   

In addition alternative measures indicate some improvement in mortality of Aboriginal and Torres Strait Islander Australians between 1991 and 2005:

• declines in mortality as measured by age-standardised death rates have been recorded in Western Australia and for females in the Northern Territory
• declines in infant mortality have been recorded in Western Australia, South Australia and the Northern Territory.
   

For more information see The Health and Welfare of Australia's Aboriginal and Torres Strait Islander Peoples, Oct 2010, cat. no. 4704.0, Wang Z and Li SQ, 2010, Mortality in the Northern Territory 1967-2006, Health Gains Planning Information Sheet, Dec 2010, Northern Territory Government, Casuarina NT and SCRGSP (Steering Committee for the Review of Government Service Provision) 2011, Overcoming Indigenous Disadvantage: Key Indicators 2011, Productivity Commission, Canberra. 

Three life expectancy at birth assumptions have been used to produce the three main series.

Aboriginal and Torres Strait Islander life expectancy at the national level has been calculated using an age-specific adjustment to allow for different patterns in mortality amongst different age groups. This adjustment could not be applied at the state and territory level. For this reason the Australian-level estimates are not strictly comparable with the state/territory level estimates. However, for the purpose of compiling estimates and projections, mortality differentials are calculated based on the relationship of 2015 to 2017 life expectancies at birth for each state/territory (without age adjustment) compared with Australia (with age adjustment).

Aboriginal and Torres Strait Islander life expectancy at birth differs between the states and territories. For the purposes of these projections, mortality differentials between each state/territory and Australia are calculated and applied to the assumed Australian life expectancies at birth to obtain assumed life expectancy at birth for the states and territories. This method assumes that the mortality differentials, based on those observed during 2015 to 2017, will remain constant throughout the projection period. 

Due to small numbers of deaths registered as Aboriginal and Torres Strait Islander it was not possible to produce Aboriginal and Torres Strait Islander life tables for Victoria, South Australia, Tasmania and the Australian Capital Territory. For the purposes of the projections it is assumed that life expectancy at birth for:

• Victoria and Tasmania are the same as that for New South Wales
• South Australia is the same as that for Western Australia
• The Australian Capital Territory is the same as that derived for the Sydney Indigenous Region.
   

To apply assumptions on life expectancy at birth for alternative geographies, Indigenous Regions (IREGs) were aggregated into two groups for each state and territory (except Tasmania and the Australian Capital Territory):

• capital city IREG (for example, Adelaide IREG)
• rest of state/territory IREGs combined (for example, Port Augusta IREG and Port Lincoln - Ceduna IREG combined).
   

To account for under-identification of deaths of Aboriginal and Torres Strait Islander people at smaller geographic level, the number of registered deaths of Aboriginal and Torres Islander people for each IREG group in 2015 to 2017 was adjusted using state and territory adjustment factors from the 2016 to 2017 Census and deaths linked data. For more information about the derivation and use of adjustment factors in the compilation of Aboriginal and Torres Strait Islander life tables for the states and territories, see Life Tables for Aboriginal and Torres Strait Islander Australians, 2015–2017. 

A life table methodology was used to obtain life expectancy at birth for 2015 to 2017 for each IREG group using adjusted deaths in conjunction with 2016 Aboriginal and Torres Strait Islander populations for each IREG group. Differentials were calculated as the ratio of Aboriginal and Torres Strait Islander life expectancy at birth for each IREG group and Australia with age adjustment. This method assumes that under-identification of Aboriginal and Torres Strait Islander deaths is consistent across all regions within each state and territory as information on under-identification is not available at IREG level. Mortality differentials are assumed to remain constant throughout the projection period. 

As noted above, Aboriginal and Torres Strait Islander life tables were not produced for Victoria, South Australia, Tasmania and the Australian Capital Territory. The following differentials have been used for IREG groups in these states and territories:

• Victoria: Melbourne IREG uses the Sydney IREG differential, the rest of Victoria IREG uses the rest of New South Wales IREG group differential
• South Australia: Adelaide IREG uses the Perth IREG differential, and the rest of South Australia IREG group uses the rest of Western Australia IREG group differential
• Tasmania uses the New South Wales state differential
• The Australia Capital Territory uses the Sydney IREG differential.
   

Aboriginal and Torres Strait Islander life expectancy at birth differentials for Remoteness Areas were calculated using the same method as that used for IREG groups. 

One assumption has been made for future net internal migration of Aboriginal and Torres Strait Islander people:

• constant levels of migration as observed in the 2016 Census based on address 5 years ago.
   

The 'place of usual residence five years ago' Census questions shows that the number of Aboriginal and Torres Strait Islander people who changed their state or territory of usual residence between:

• 2011 and 2016 was 25,960
• 2006 and 2011 was 21,340
• 2001 and 2006 was 18,440.
   

This measure was unable to account for:

• Aboriginal and Torres Strait Islander children under five years of age on Census night
• people whose place of residence five years ago was overseas
• people whose state or territory of usual residence five years ago was not recorded.
   

In addition, Aboriginal and Torres Strait Islander people overseas on Census night were not counted in the Census. 

State or territory of usual residence on Census night was cross-tabulated with state or territory of usual residence five years ago to obtain net intestate migration for each state and territory for 2011 to 2016.

These figures are affected by a number of data quality issues, including Census net undercount and records for which Indigenous status was not stated. To account for these, net interstate migration estimates were adjusted by a proportion calculated by dividing Aboriginal and Torres Strait Islander ERP by Aboriginal and Torres Strait Islander Census counts, for each state and territory.

The adjusted net interstate migration estimates were then divided by five to obtain annual movements, which were assumed to remain constant over the projection period. In addition, they were used as constraints on migration assumptions for Indigenous Regions and Remoteness Areas.

The age/sex profile of intestate migration was derived from the 'place of usual residence one year ago' question from the 2016 Census. Arrival and departure rates for the states and territories were calculated by single year of age and sex and adjustments were made where appropriate to ensure the age/sex profiles of projected populations were plausible. All age/sex arrival and departure disaggregations were constrained by the net internal migration assumption at the state/territory level. 

Annual net migration estimates for each IREG were calculated in the same way as for the states and territories, and were assumed to remain constant over the 15-year projection period.

Annual net migration estimates for each Remoteness Area were calculated in the same way as for states and territories, and were assumed to remain constant over the 15-year projection period. 

One assumption has been made for future net overseas migration of Aboriginal and Torres Strait Islander people:

• zero overseas migration, with zero arrivals and zero departures.
   

According to the 2016 Census there were 1,969 Aboriginal and Torres Strait Islander people resident in Australia in 2016 who lived overseas in 2011. Slightly fewer numbers of Aboriginal and Torres Strait Islander people resident in 2011 also lived overseas in 2006 (1,375 persons). 

This level of in-migration has a negligible effect on the size of the future Aboriginal and Torres Strait Islander population. In addition, there will also be some level of out-migration leading to an even smaller net migration rate.

Zero unexplained growth has been assumed for this series of projections.

The Aboriginal and Torres Strait Islander population has a relatively young age structure with a median age of 22.9 years in 2016 (37.8 years for the Non-Indigenous population).

• in 2006 the median age was 21.2 years
• by 2031 the median age is projected to be between 25.5 and 26.5 years.

The Aboriginal and Torres Strait Islander population is projected to increase across all age groups between 2016 and 2031.

The number of children (0–14 years) is 274,300 in 2016. This is projected to:

• increase to between 309,200 and 350,200 in 2031
• decrease as a proportion of the population, from 34.4% in 2016 to between 29.6% and 32.0% in 2031.
   

The number of people aged 15–64 years is 490,000 in 2016. This is projected to:

• increase to between 653,500 and 655,900 in 2031
• remain stable as a proportion of the population, from 61.4% in 2016 to between 60.0% and 62.5% in 2031.
   

The number of people aged 65 years and over is 34,000 in 2016. This is projected to:

• increase to between 83,300 and 86,900 in 2031
• increase as a proportion of the population, from 4.3% in 2016 to between 7.9% and 8.0% in 2031.
   

All three series project continuing population growth in the majority of Indigenous Regions between 2016 and 2031:

The Aboriginal and Torres Strait Islander population in Brisbane is projected to be the fastest growing of all Indigenous regions, with an average annual growth rate of between 2.7% and 3.0% per year. This is followed by:

• Australian Capital Territory (between 2.6% and 2.9%)
• Victoria, excluding Melbourne (between 2.5% and 2.8%).
   

Katherine is the only Indigenous region where the Aboriginal and Torres Strait Islander population is projected to decrease between 2016 and 2031. This can be attributed to assumed net migration loss (see section Assumptions, Table 15).

Sensitivity analysis was undertaken into the effect of fertility assumptions on the size of the future Aboriginal and Torres Strait Islander population and the number of projected births. The below table shows the projected Aboriginal and Torres Strait population and births in 2031 under three fertility assumptions:

Based on the Series B fertility assumption (1.0% annual decline in fertility rates):

• Aboriginal and Torres Strait Islander population of Australia is projected to reach 1,065,200 people in 2031 (up from 798,400 in Series B in 2016)
• births are projected to increase from 18,970 in 2017 to 24,310 in 2031.
   

Assuming fertility rates remain constant (Series D) it is projected that:

• Aboriginal and Torres Strait Islander population of Australia will reach 1,081,900 people in 2031 (up from 1,065,200 in Series B in 2031)
• births will be higher than in Series B in 2031 (26,660 compared with 24,310)
• this will result in more Aboriginal and Torres Strait Islander children aged 0-14 years in 2031 than in Series B (341,600 compared with 324,900).
   

Assuming a 1.5% annual decline in fertility rates (Series E):

• Aboriginal and Torres Strait Islander population of Australia is projected to reach 1,057,400 people in 2031 (down from 1,065,200 people in Series B in 2031)
• births will be lower than in Series B in 2031 (23,250 compared with 24,310 )
• this will result in fewer Aboriginal and Torres Strait Islander children aged 0-14 years in 2031 than in Series B (317,100 compared with 324,900).
   

Sensitivity analysis was undertaken into the effect of paternity assumptions on the size of the future Aboriginal and Torres Strait Islander population and the number of projected births.

The below table shows the projected Aboriginal and Torres Strait population and births in 2031 under the three paternity assumptions:

Based on the Series B paternity assumption (1.0% annual increase in paternity rates):

• Aboriginal and Torres Strait Islander population of Australia is projected to reach 1,065,200 people in 2031 (up from 798,400 in 2016)
• births are projected to increase from 18,970 in 2017 to 24,310 in 2031.

Assuming paternity rates remain constant (Series F) it is projected that:

• Aboriginal and Torres Strait Islander population of Australia will reach 1,057,600 people in 2031 (down from 1,065,200 in Series B in 2031)
• births will be lower than in Series B in 2031 (23,170 births compared with 24,310)
• This will result in fewer Aboriginal and Torres Strait Islander children aged 0-14 years in 2031 than in Series B (317,200 compared with 324,900).

Assuming a 2.0% annual increase in paternity rates (Series G):

• Aboriginal and Torres Strait Islander population of Australia is projected to reach 1,073,600 people in 2031 (up from 1,065,200 people in Series B in 2031)
• births will be higher than in Series B in 2031 (25,610 births compared with 24,310)
• This will result in more Aboriginal and Torres Strait Islander children aged 0-14 years in 2031 than in Series B (333,300 compared with 324,900).
   

Sensitivity analysis was undertaken into the effect of life expectancy at birth assumptions on the size of the future Aboriginal and Torres Strait Islander population and the number of projected deaths.

The below table shows the projected Aboriginal and Torres Strait population and deaths in 2031 under the three life expectancy at birth assumptions:

Based on the series B life expectancy assumption (annual increase of 0.40 years for males and 0.25 years for females):

• Aboriginal and Torres Strait Islander population of Australia is projected to reach 1,065,200 people in 2031 (up from 798,400 in 2016)
• deaths are projected to increase from 3,620 in 2017 to 4,570 in 2031.
   

Assuming an annual increase of 0.25 years for males and 0.20 years for females (series I) it is projected that:

• Aboriginal and Torres Strait Islander population of Australia will reach 1,061,400 people in 2031 (down from 1,065,200 in Series B in 2031)
• deaths are projected to be higher than in Series B in 2031 (5,040 deaths compared with 4,570).
   

Assuming an annual increase of 0.45 years for males and 0.35 years for females (series H):

• Aboriginal and Torres Strait Islander population of Australia is projected to reach 1,067,900 people in 2031 (up from 1,065,200 in Series B in 2031)
• deaths are projected to be lower than in Series B in 2031 (4,230 deaths compared with 4,570).
   

One assumption has been made for future net internal migration of Aboriginal and Torres Strait Islander people:

• constant levels of migration as observed in the 2016 Census of Population and Housing based on address 5 years ago.
   

The Census of Population and Housing (Census) provides the basis of Australia's official population estimates. For the total Australian population, quarterly estimates can be produced between Censuses by applying components of population growth (births, deaths and migration) to the latest Census-based estimate. Generally speaking, the accuracy of the Census and component data means that only minor adjustments to the population figures occur after each Census.

However, Aboriginal and Torres Strait Islander Census counts and the quality of data on births, deaths and migration of Aboriginal and Torres Strait Islander people do not support the use of the standard approach to population estimation. Instead, the ABS uses assumptions about future fertility, paternity, life expectancy and migration to project figures out from each Census. At the same time, it is also necessary to backcast the Aboriginal and Torres Strait Islander population, because each Census count is sufficiently different from the last, due to a range of non-demographic factors, such as changing levels of self identification in the Census.

The uncertainty in the Census and component data occurs because:

• Aboriginal and Torres Strait Islander population is very small compared with the total Australian population (around 3.3%), and
• Aboriginal and Torres Strait Islander population requires people not only to be counted in the Census and component datasets, but also to be identified as being of Aboriginal or Torres Strait Islander origin.
   

The differences between the Aboriginal and Torres Strait Islander population estimates derived from each Census thus tend to be larger than demographic changes can account for. Each Census-based estimate reflects both the desire of people at that time to be identified as being of Aboriginal or Torres Strait Islander origin, and the ability at that time for the information to be effectively collected in the Census.

The Australian Census Longitudinal Dataset (ACLD) suggests that a certain proportion of the population will be counted as Aboriginal or Torres Strait Islander in one Census, but as non-Indigenous in the next, and vice versa – see Census of Population and Housing: Understanding the Increase in Aboriginal and Torres Strait Islander Counts for further information.

Graph 8, below, shows the percentage increase in estimated resident population (ERP) between Censuses for both the Aboriginal and Torres Strait Islander population and the total Australian population, for the last five intercensal periods. The change in the total population between Censuses remains lower than 10%, and is largely consistent with birth, death and migration rates observed between Censuses. This is not the case for the Aboriginal and Torres Strait Islander population, for which implausible demographic trends would need to have occurred to account for the intercensal difference.

Between 2011 and 2016, the Aboriginal and Torres Strait Islander Census counts increased by 18.4% (100,800 persons). Of this increase:

• 78.6% can be accounted for by explainable demographic factors of population changes - that is, births, deaths and migration
• propensity to identify was a major contributor to the remaining 21.4% increase, not due to demographic factors.
   

For more information see Census of Population and Housing: Understanding the Increase in Aboriginal and Torres Strait Islander Counts and Occasional Paper: Population Issues, Indigenous Australians (cat. no. 4708.0)

Other collections, such as surveys and administrative datasets also rely on a person's Indigenous status to be accurately reported and recorded, and therefore may likewise be susceptible to differing rates of identification, which may also vary over time. The changing rates of identification of Aboriginal and Torres Strait Islander people in the Census and other datasets create challenges when comparing data about this population over time. For further information, see Information Paper: Perspectives on Aboriginal and Torres Strait Islander Identification in Selected Data Collection Contexts (cat. no. 4726.0) for further information.

After each Census, the ABS creates a time series for the population based on that Census count, by projecting and backcasting around this estimate. The backcast series shows what the Aboriginal and Torres Strait Islander population (based on the latest Census) would have been in previous periods, based purely on demographic change. Similarly, the projected series shows how the currently identified Aboriginal and Torres Strait Islander population may change in future years, if certain demographic assumptions were to hold. Each Census-based series is independent from the others.

Graph 9 shows the five different population series that cover the period 1996 to 2016, as well as how each year's estimated population would change if a simple, straight line interpolation was applied between successive Census-based estimates.

Often, population estimates for Aboriginal and Torres Strait Islander people are used as the denominator for rates, to compare data for the Aboriginal and Torres Strait Islanders population with the non-Indigenous population, or to create time-series indicators about how various aspects of the well-being of Aboriginal and Torres Strait Islander people are changing over time. The use of different series of population estimates shown in graph 9 will clearly impact on such indicators.

Following are some examples of the impact that the choice of Aboriginal and Torres Strait Islander population estimates can have on a rate. The examples use six different series to demonstrate this:

• the 2016 Census-based series
• the 2011 Census-based series
• the 2006 Census-based series
• a series which uses each Census-based series for the two years before and after that Census (option 1)
• a series which transitions between Census-based series in a way that minimises the 'jump' in the transition year (option 2)
• linear interpolation between Census estimates.
   

The use of different Census-based Aboriginal and Torres Strait Islander population estimates, while showing a similar pattern of change over time, has a considerable impact on the level of historical child mortality rates, as shown in graph 10. When using a combination of series, as shown in graph 11, the downward trend in the rate is more obvious.

In the case of school enrolments data, the use of previous Census-based series generates impossible results, with rates exceeding 100%. In contrast, when using a combination of Census-based population series (graph 13), the enrolment rates remain plausible throughout, although there is no longer a clear trend in the time-series. Further analysis would be needed to determine the most appropriate choice of Aboriginal and Torres Strait Islander population estimates. In particular, the choice may depend on an understanding of how identification rates in the enrolment data (numerator) had changed over time.

In the case of age-standardised death rates, the use of different Aboriginal and Torres Strait Islander population estimates changes the direction of the trend.

In each of the examples above, of the three methods of transition between population estimate series shown, the time-series rate is smoothest when using a linear interpolation between Census year estimates. Changing from one Census-based series to the next results in a sharp drop in the rate at the changeover point. This can be seen at points 2009, 2013 and 2014. 2018 would be the equivalent 'decision point' for the current intercensal period. The extent of the 2018 transition will not be known until after the 2021 Census-based ERP series becomes available.

The question of which historical population series to use depends on the purposes of the analysis. The following provides guidelines to help in making these decisions.

The 2016-based series is the most accurate and up-to-date series currently produced by the ABS, including in terms of the methodology used in the Census collection and in the estimation/projection processes. The 2016-based series can generally be used for any of the following scenarios:

• for demographic analysis of the Aboriginal and Torres Strait Islander population
• for forward-looking analysis (i.e. from 2016 onwards), for any purpose
• as the denominator of rates being compared over time, if:
• the time series is short, generally no further back than the penultimate (2011) Census
• the numerator data are known to have been fairly consistently high over time
• analysis is restricted to remote geographies, where the impact of increased identification is much lower than in non-remote areas
• when there is a known quality issue in the data from earlier Censuses.
   

Using a range of different Census-based population estimate series could be considered when:

• transitioning from one series to the next will maximise consistency of identification levels and coverage between the numerator and the denominator
• historical rates are thought to be artificially deflated when using the 2016-based population estimates (usually due to lower identification rates in the numerator series in earlier years)
• there is a known relationship between identification in the numerator data and the Census data. Data linkage may be used to inform on this relationship – for example see Linking Death registrations to the 2016 Census. This relationship may be applied to the 2016-based series as a factor, or be used to inform the choice of a transitional series
• data confrontation using supplementary data sources indicates that the 2016-based population estimates do not produce a plausible result.
   

In some cases, an alternative data source may exist which is more comparable/consistent with the numerator data, and could be used rather than a population estimate series. For example,

• survey data should be compared to the survey population. That is, re-weighting past surveys to the latest population estimate series is not generally recommended
• analysis of Census data should be based on Census counts rather than population estimates see Estimates of Aboriginal and Torres Strait Islander Australians, June 2016, Technical Note 1: Estimated Resident Aboriginal and Torres Strait Islander Population - Method of Calculation.
• numerator data could be compared to a denominator that is internally consistent, rather than to population estimates - for example retention rates (15 year-old students in 2018 as a percentage of 12 year-old students in 2015) produces a more coherent time-series than enrolment rates (15 year-old students as a percentage of 15 year-old population).
   

If in any doubt, the ABS recommends that data users conduct their own analysis, for example similar to that illustrated in the examples above. This will highlight the impact of non-demographic changes on their particular area of interest.

A new series for Aboriginal and Torres Strait Islander population estimates will be produced following the 2021 Census. Depending on how the 2021 Census-based estimate compares with the 2016 Census-based estimate, current indicator trends may change as a result of rebasing any population estimates to the new Census.

Aboriginal and Torres Strait Islander population projections are produced to illustrate potential future demographic changes to the currently identified population. The 2016-based projections therefore do not include any assumption variable on propensity to identify. Anyone considering the future population should consider their requirements for a projection based on a change in propensity to identify, and note that the ABS projections cannot be used for this purpose.

Option 1 involves deriving non-Indigenous population estimates by subtracting Aboriginal and Torres Strait Islander backcast estimates and projections from the total Australian estimated resident population (ERP) for a given year. This option is currently being used for national reporting purposes. The advantages and disadvantages are covered below.

Advantages:

• This option uses the best available number for each population.
   

Disadvantages:

• A mixture of methods is being used - ERP for the total population and projections and backcast estimates for the Aboriginal and Torres Strait Islander population.
   

Option 2 involves deriving non-Indigenous population estimates by subtracting Aboriginal and Torres Strait Islander backcast estimates and projections from total population projections. The advantages and disadvantages of this option are detailed below.

Advantages:

• The methods for calculating each population are comparable as both populations are projections
• Both sets of projections are derived from the same base point and at approximately the same point in time.
   

Disadvantages:

• Both sets of projections are based on assumptions of future levels of fertility, mortality and migration (i.e. it is not measured data)
• Non-Indigenous population is more likely to change demographically (through fluctuations in NOM) than the projections can effectively foresee.
   

Non-Indigenous population estimates derived using Options 1 and 2 are used in calculating child (0-4 years) and age-standardised death rates for NSW, Qld, SA, WA, NT and the total of these five jurisdictions for the periods 2011 to 2015, 2012 to 2016 and 2013 to 2017. Method of calculation is the same as that used for the National Indigenous Reform Agreement (NIRA), National Healthcare Agreement (NHA) and Health Performance Framework (HPF) reporting (that is, the average of five years of deaths is divided by the mid-point population estimates and multiplied by 100,000). Results show that the difference between the rates based on non-Indigenous population derived using Option 1 and Option 2 is minimal (around 2%). This suggests that the non-Indigenous death rates are not particularly sensitive to the methods used in deriving non-Indigenous population estimates.

The ABS consulted a number of expert stakeholders who agreed that Option 1 is the preferred method for deriving non-Indigenous population estimates (that is, by subtracting Aboriginal and Torres Strait Islander backcast estimates and projections from total population ERP). This option uses the best available number for each population and hence yields better quality estimates for non-Indigenous population. However, Option 1 cannot be used when total population ERP is not available (for example, when considering future trends). In such situations, Option 2 should be used.

As with all advice the ABS provides, advice given in this article should be considered in relation to the specific requirements of data users and the appropriateness of the advice for their needs.

Population projections illustrate how the Australian Aboriginal and Torres Strait Islander population would change in the future if specific patterns of fertility and paternity (births), mortality (deaths) and migration were to occur. These potential scenarios are based on assumptions regarding what could happen, based on recent demographic trends. As we cannot know what will happen in the future, a number of different assumptions are used to illustrate a range of possible outcomes. These outcomes include the level, growth, distribution and composition of the Aboriginal and Torres Strait Islander population.

Population projections 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. For example, a high growth area with a young population may require investment in public transport, day care centres and schools. Aboriginal and Torres Strait Islander population projections are important for supporting national reporting on the health and socio-economic wellbeing of the Aboriginal and Torres Strait Islander population.

ABS population projections do not predict or forecast how the Aboriginal and Torres Strait Islander population will look in the future. They do not incorporate any non-demographic factors which influence population change, such as changes in an individual’s decision to identify as Aboriginal and/or Torres Strait Islander, government policy, improvements in health treatment or the occurrence of natural disasters. Projections only show how the Aboriginal and Torres Strait Islander population would change if the demographic assumptions made were to eventuate over the projection period. This may or may not happen.

ABS uses a method that involves making assumptions about future levels of Aboriginal and Torres Strait Islander fertility, paternity, mortality, net overseas migration and net interstate migration based on recent observed trends. These are applied to a starting (or base) population, split by sex and single year of age, to obtain a projected population for the following year. The assumptions are then applied to this new (projected) population to obtain a projected population for the next year, and so on through to the end of the projection period.

The Aboriginal and Torres Strait Islander population of Australia as at 30 June 2016 is used as the base for the projection series. The Aboriginal and Torres Strait Islander population is then projected for the period 30 June 2017 to 30 June 2031 for Australia, States and Territories, Remoteness Areas and Indigenous Regions.

Various population growth and demographic information is taken into account in the creation of Aboriginal and Torres Strait Islander population projections. These include:

• Children ever born data from several Censuses
• Total and age-specific fertility and paternity (i.e. births to Aboriginal and Torres Strait Islander fathers, where the mother’s Indigenous Status is non-Indigenous or not stated) rates
• Ratios of males to females
• Life expectancy at birth
• Total and age-specific death rates;
• Migration flows internationally and interstate.

Assumptions are based on demographic trends observed over the past two decades in Australia. The ABS also consults various experts, government department representatives and other advisory groups at the national and state/ territory level. Three assumptions (high, medium and low) are used for fertility, paternity and mortality. Net interstate migration has one assumption based on the rates of interstate arrivals and departures observed in the 2016 Census. Net overseas migration is assumed to be zero, that is, no arrivals or departures. Observed differences between states and territories, Remoteness Areas and Indigenous Regions are also incorporated. There are nine possible combinations of assumptions at the national and state/territory levels, all of which yield different potential populations.

Future uncertainty, along with the subjective nature of assessing recent trends, means that it is useful to provide a range of possible outcomes (rather than a single series) for the future size, distribution, growth and age and sex structure of Australia's Aboriginal and Torres Strait Islander population. The ABS presents three projection series (Series A, B and C) to provide a useful and accessible range of projections for analysis and discussion.

22/07/2021 - Minor changes to projected data for 2017 to 2031 to correct a processing error. The minor changes will not materially impact calculated rates.

12/07/2019 - Datacube 1, 'Estimates and Projections, Aboriginal and Torres Strait Islander Australians, 2006 to 2031', has been updated to include missing age group labels in the 'Persons' category that was published on 11 July 2019.

Graph 3 in 'Assumptions' section, 'Average number of children ever born to Aboriginal and Torres Strait Islander women, Census years' has been updated to reflect correct Census years data.