Life Tables for Aboriginal and Torres Strait Islander Australians

This publication contains life expectancy estimates for Aboriginal and Torres Strait Islander people for Australia, selected states/territory, remoteness area and SEIFA (Index of Relative Socio-Economic Disadvantage) for the reference period from 2015 to 2017. These are life expectancy estimates for the Aboriginal and Torres Strait Islander population as measured in the 2016 Census and adjusted for net undercount using Post Enumeration Survey (PES) results, which may not represent all Aboriginal and Torres Strait Islander people in Australia. As such, a number of data quality issues need to be considered when reporting and interpreting Aboriginal and Torres Strait Islander life expectancy estimates presented in this release.

The standard approach to compiling life tables and resulting life expectancy estimates requires complete and accurate data on the average number of deaths that occur in a period, and reliable estimates of the population (at the mid-point of the period) exposed to the risk of dying. These data are required by age and sex, so as to calculate age-sex specific death rates. In the case of Aboriginal and Torres Strait Islander mortality estimation, this situation is less than perfect. Registration of Aboriginal and Torres Strait Islander deaths have some limitations compared to those for the entire population. In addition, a number of quality issues associated with Aboriginal and Torres Strait Islander population estimates exist. In combination, these present particular methodological challenges to compiling high quality life tables and making comparisons over time. For more information see Quality issues with Aboriginal and Torres Strait Islander deaths and population data.

Changes in people's propensity to identify as Aboriginal and Torres Strait Islander between Census years have resulted in compositional changes in the Aboriginal and Torres Strait Islander population over time. This is particularly prevalent in Major Cities. Between the 2011 and 2016 Censuses, the Aboriginal and Torres Strait Islander population increased by 18.4% (100,803 people). Analysis shows that 78.6% of this increase can be explained by demographic factors, such as births, deaths and overseas migration. The remaining 21.4% (or 21,531) of the increase in Census counts that could not be explained by demographic factors can be attributed to changing propensities to identify and methodological improvements in coverage and response rates in the Census (see Census of Population and Housing: Understanding the Increase in Aboriginal and Torres Strait Islander Counts, 2016).

Aboriginal and Torres Strait Islander people living in Major Cities (where most of the 2011 to 2016 population increase occurred) were the main contributors to intercensal increases in Year 12 attainment, non-school qualifications, labour force participation and higher personal weekly income. These changes pose significant challenges in the interpretation of Aboriginal and Torres Strait Islander life expectancy estimates over time.

While the estimates in this release show a small improvement in life expectancy estimates and a reduction in the gap between the periods from 2010 to 2012 and 2015 to 2017, this improvement should be interpreted with considerable caution as the population composition has changed during this period as outlined above. This release provides information on Aboriginal and Torres Strait Islander life expectancy in different geographic areas, to assist policy markers target initiatives for improved life expectancy gains.

The ABS recommends that estimates be considered in context with other health performance measures to adequately assess progress in 'Closing the Gap' measures.

The standard approach to compiling life tables and resulting life expectancy estimates requires complete and accurate data on the average number of deaths that occur in a period, and reliable estimates of the population (at the mid-point of the period) exposed to the risk of dying. These data are required by age and sex, so as to calculate age-sex specific death rates.

In the case of Aboriginal and Torres Strait Islander mortality estimation, this situation is less than perfect. Information on death registrations of Aboriginal and Torres Strait Islander Australians has limitations and a number of quality issues associated with Aboriginal and Torres Strait Islander population estimates exist. In combination, these present particular methodological challenges to compiling high quality life tables and making comparisons over time.

To calculate estimates of life expectancy using direct methods, it is important to ensure that the classification of records as Aboriginal and Torres Strait Islander occurs in a consistent manner in both the numerator (deaths) and the denominator (population).

The Indigenous Mortality Study was first conducted as part of the ABS Census Data Enhancement (CDE) project for the 2006 Census. It has been repeated for subsequent Censuses. Most recently, the CDE project consists of a number of studies which have brought together data from the 2016 Census of Population and Housing and other specified datasets.

For more information on the 2016 CDE project, see the paper: Linking Death registrations to the 2016 Census.

The aims of the CDE Indigenous Mortality Study were to:

• assist in understanding the differences in recording of Indigenous status between death registrations and Census data; and
• assess the under-identification of Aboriginal and Torres Strait Islander deaths in death registrations records.
   

The CDE Indigenous Mortality Study involved linking Census records with death registration records to examine differences in the reporting of Indigenous status across the two datasets. Specifically the study linked 2016 Census records with all registered deaths that occurred from 9 August 2016 to 28 September 2017, with a slightly longer range than 12 months to allow time for all relevant deaths to be registered and processed.

In the absence of any unique identifier in the Census and deaths datasets, linking was performed using probabilistic methods. Three groups of variables, name (first name and surname), personal characteristics (date of birth, age, sex, place of birth, year of arrival and marital status), and geographic information (street number, street name, suburb, mesh block and postcode) were used to link death records to Census records. Variables common to both datasets were standardised to ensure consistent coding and formatting. The two datasets were linked in a way that was independent of reported Indigenous status so that any future analysis would not be affected by bias introduced in the linking process. For this reason, Indigenous status was not used as a linking variable.

The 2016 Death registrations to Census linkage project builds on the success of other data integration programs, incorporating enhancements from these programs.

The main enhancements implemented for the 2016 project included:

• use of non-sequential probabilistic linking of 2016 Census data to death records (as opposed to sequential probabilistic linking used in 2011),
• use of alternative address information from Census and Death registrations to improve linkage of records between datasets,
• improving name repair processes, where the rarity of a name was used in evaluating the quality of links established, and
• an enhanced clerical review strategy resulting in higher quality links.

Internationally, similar record linkage studies have been conducted in New Zealand where the 1981, 1986, 1991, 1996 and 2001 Censuses were each anonymously and probabilistically linked to three years of subsequent deaths data, allowing a comparison of ethnicity recording (Ajwani et al., 2003; Blakely et al., 2002a; Blakely et al., 2002b). Large nationally representative studies based on linked Census and deaths data have also been conducted in the United Kingdom, France, Sweden and Netherlands. The results from these studies have been used in various ways including the provision of evidence for policy decisions and the setting of policy targets for special intervention programs.

The number of Census and death registration records eligible for linking and the percentage of death records linked are presented in Table 9. The linking process used 177,380 death records and 22,485,854 Census records. These Census counts are different from the estimated resident population, as discussed in Population estimates of Aboriginal and Torres Strait Islander Australians.

Of the 177,380 death records, 159,657 (90.0%) records were linked to one of 22,485,854 eligible Census records. Of the 3,246 Aboriginal and Torres Strait Islander death records, 2,315 (71.3%) were linked.

The number and percentage of death records linked to Census records by selected characteristics of deceased persons are presented in Table 10. A slightly higher linkage was achieved for females (91.4%) compared with males (88.6%). The linkage rate varied considerably by age, being lowest for 0-14 year old deceased persons (63.4%). This may be due to the comparatively high Census undercount rate in this age group. The linkage rate was highest for 75 years and older deceased persons (92.9%).

The linkage success varied by state of usual residence as reported on the death registration form. Rates were highest for South Australia (91.5%) and lowest for the Northern Territory (72.9%). All other states and territories had linkage rates between 88.8% and 90.9%. The low linkage rate for the Northern Territory reflects comparatively low linkage rates for both the Aboriginal and Torres Strait Islander and non-Indigenous populations. The linkage rate was similar for married and widowed persons (92.2 and 92.6% respectively). The linkage rate was lower for deaths which occurred within six months of the Census (88.8%) than those which occurred beyond six months after the Census (91.0%).

The linkage success also varied by Indigenous status recorded on the death registration form. People of non-Indigenous origin on the death registration form had a considerably higher linkage success (90.4%) compared with people of Aboriginal and Torres Strait Islander origin (71.3%). A more strict approach to implementing the 2016 linkage clerical review resulted in a lower, but more accurate linkage rate than in the period from 2010 to 2012. For further information about the linkage methodology, see Information Paper: Linking Death registrations to the 2016 Census.

The CDE study allows a direct comparison of Indigenous status recorded on the death registration and the Census data for what is highly likely to be the same individual, and enables estimation of the undercoverage of Aboriginal and Torres Strait Islander deaths in the death registration system.

Table 11 presents the outcomes of the CDE study for Aboriginal and Torres Strait Islander deaths in Australia. It provides a cross-classification of the linked death registrations and Census records by the Indigenous status and age groups recorded in the respective records. Similar tables for other states and territory (without an age breakdown) where there are sufficient deaths available are in Data downloads, Table 4: Summary of linked deaths by Indigenous status, deaths registrations and Census identification, selected States and Territory and Australia, from 2016 to 2017.

The table highlights a number of features:

• of the 2,611 linked records identified as Aboriginal and Torres Strait Islander on the Census file, only 1,885 (72%) were identified as Aboriginal and Torres Strait Islander in death registrations;
• the 1,885 records identified as Aboriginal and Torres Strait Islander in both datasets represented 81% (that is 1,885 / 2,315 * 100) of linked deaths identified as Aboriginal and Torres Strait Islander in death registrations;
• there is misidentification of Indigenous status between the Census and death registrations (for example, Aboriginal and Torres Strait Islander in death registrations but non-Indigenous in Census, and vice versa);
• the overall Aboriginal and Torres Strait Islander deaths identification rate indicated by these statistics is 89% (that is, 2,315 / 2,611* 100).
   

The above suggests that while there appears to be misidentification of Indigenous status between the Census and death registrations, the overall identification rate in the death registrations collection is quite high at the national level (89%).

At the same time, it needs to be recognised that at the national level, about 29% of Aboriginal and Torres Strait Islander deaths as recorded on the death registration form could not be linked to a Census record. This would occur due to missing or inconsistent information in the fields being used for linking and also undercount of the Aboriginal and Torres Strait Islander population in the Census counts. Despite these issues, it is considered that the linked data provide reasonable estimates of the identification rate of Aboriginal and Torres Strait Islander deaths.

For the purpose of compiling Aboriginal and Torres Strait Islander life tables, the Aboriginal and Torres Strait Islander ERP used was derived from Census counts adjusted by results of the Post Enumeration Survey (PES). The PES provides an independent check on Census coverage and also identifies key demographic characteristics of the population that have been missed or overcounted in the Census. In compiling Aboriginal and Torres Strait Islander ERP, Indigenous status reported by the PES was considered more reliable than that recorded in the Census.

Therefore, to be consistent with Aboriginal and Torres Strait Islander ERP calculations, the number of deaths reported as Aboriginal and Torres Strait Islander in Census in the CDE linked data were adjusted to a PES basis. It should be noted that these adjustments were only in respect of misclassifications of Indigenous status in the linked file. No attempt was, or could be, made for undercount identified in the PES; this is reflected in the non-matched death registrations.

Thus, the Aboriginal and Torres Strait Islander deaths identification rate using the linked data was derived by:

1. calculating the propensities, from PES, of being Aboriginal and Torres Strait Islander in PES given Census Indigenous status (to align the Census Indigenous status with the PES Indigenous status);
2. applying the propensities to counts from the CDE linked data to obtain the expected number of deaths in Census on a PES basis; and
3. taking the ratio of the number of deaths reported as Aboriginal and Torres Strait Islander in death registrations to that reported in Census on a PES basis to calculate the Aboriginal and Torres Strait Islander deaths identification rate.

The following step by step example illustrates the calculation of the identification rate of Aboriginal and Torres Strait Islander deaths for Australia using the improved method that include age-specific identification rates when calculating the underidentification adjustment.

The propensities are calculated for persons who matched to Census and responded as Aboriginal and Torres Strait Islander in the PES to the Census Indigenous status question. They were estimated by the three response classes for the Census Indigenous status question: Aboriginal and Torres Strait Islander, non-Indigenous and not stated.

The following example will refer to data for the 0–14 years age group in Table 12:

• P(ATSI/ATSI) = propensity of being Aboriginal and Torres Strait Islander in PES given Census Indigenous status is 'Aboriginal and Torres Strait Islander' is 1,713 / 1,818 = 0.9422
• P(ATSI/NI) = propensity of being Aboriginal and Torres Strait Islander in PES given Census Indigenous status is 'non-Indigenous' is 90 / 17,293 = 0.0052
• P(ATSI/NS) = propensity of being Aboriginal and Torres Strait Islander in PES given Census Indigenous status is 'not stated' is 10 / 176 = 0.0568
   

The above propensities are based on the unweighted PES data. In calculating Aboriginal and Torres Strait Islander ERP, weighted PES information was used. Therefore, to be consistent with Aboriginal and Torres Strait Islander ERP calculations, the propensities were calculated using the weighted PES data. This gave, for 0–14 years age group, P(ATSI/ATSI) = 0.8999 P(ATSI/NI) = 0.0044 and P(ATSI/NS) = 0.0446

The Australia level propensities P(ATSI/NI) and P(ATSI/NS) calculated above are based on relatively small numbers of PES responses (90 and 10 respectively for the 0–14 years age group). These propensities calculated at the state/territory level, while not disaggregated by age, are still unreliable as they are based on considerably smaller numbers of PES responses. To overcome this problem, national level P(ATSI/NI) and P(ATSI/NS) are used for the states and territories (though without any disaggregation by age, as outlined under Calculation of adjustment factor for the states and territory).

The expected number of deaths in the Census in CDE linked data file, for persons aged 0–14 years, using PES Aboriginal and Torres Strait Islander propensities is:

• = 36 * P(ATSI/ATSI) + 393 * P(ATSI/NI) + 6 * P(ATSI/NS)
• = 36 * 0.8999 + 393 * 0.0044 + 6 * 0.0446
• = 34
   

where the numbers 36, 393 and 6 are Aboriginal and Torres Strait Islander, non-Indigenous and not stated deaths in Census for the 0–14 years age group (Table 11).

The estimate of the Aboriginal and Torres Strait Islander deaths identification rate is then calculated by taking the ratio of the number of deaths reported as Aboriginal and Torres Strait Islander in death registrations to the number of deaths expected to be recorded as Aboriginal and Torres Strait Islander in Census using the PES Aboriginal and Torres Strait Islander propensities:

= 29 / 34

= 0.84

where 29 is the Aboriginal and Torres Strait Islander deaths in death registrations for the 0–14 years age group (Table 11).

The adjustment factor is taken to be the reciprocal of the identification rate of Aboriginal and Torres Strait Islander deaths:

= 1 / 0.84

= 1.19

In the linked data, 29 records for the 0–14 years age group were reported as Aboriginal and Torres Strait Islander on the death registration form (Table 11). Of deaths linked to the Census, 34 were recorded as Aboriginal and Torres Strait Islander, after adjustment for classifying Indigenous status in the way that PES does. This means that fewer deaths were identified as Aboriginal and Torres Strait Islander in death registrations than were expected in Census on a PES basis. Therefore, for the 0–14 age group, the number of Aboriginal and Torres Strait Islander deaths according to death registrations needed multiplying by an adjustment factor of 1 / 0.84 = 1.19 to be comparable to the Aboriginal and Torres Strait Islander deaths expected to be recorded as such in the Census on a PES basis.

Steps 1–4 were repeated to calculate identification rates for the 15–59 and 60+ age groups. Identification rates were 0.93 and 0.92 for the 15–59 and 60+ age groups respectively.

The procedure described above was used to derive Aboriginal and Torres Strait Islander deaths identification rates at the Australia level only. Identification rates for states, territory, remoteness areas and Index of Relative Socio-Economic Disadvantage were calculated using a similar method but without using age-specific identification rates. This method is detailed fully in Experimental Life Tables for Aboriginal and Torres Strait Islander Australians, 2005-2007.

Due to small numbers of Aboriginal and Torres Strait Islander deaths in Victoria, South Australia, Tasmania and the Australian Capital Territory, it was not feasible to derive separate reliable Aboriginal and Torres Strait Islander deaths identification rates for these jurisdictions. Therefore, a single Aboriginal and Torres Strait Islander deaths identification rate was derived by grouping these together.

There is considerable variation in the identification rates at the state/territory level (Table 14). The estimate is less than 1.0 for New South Wales, Western Australia and Victoria/South Australia/Tasmania/Australian Capital Territory/OT combined, which indicates a level of under-identification of Aboriginal and Torres Strait Islander deaths in death registrations relative to the Census on a PES basis. In contrast, Queensland and the Northern Territory indicates a slight over-representation of Aboriginal and Torres Strait Islander deaths in death registrations relative to the Census for linked records; that is, persons who are identified as Aboriginal and Torres Strait Islander in the death registrations collection exceeded those who identified as Aboriginal and Torres Strait Islander in the Census on a PES basis. There is no clear reason as to why this might be the case, although there is evidence that some Aboriginal and Torres Strait Islander deaths have a state of usual residence on the death registration that is different to the Census.

Aboriginal and Torres Strait Islander deaths identification rates for the period 2015 to 2017 are similar to those for 2010 to 2012, with the exception of Queensland for which the identification rate substantially increased to 1.03 in the 2015 to 2017 reference period, from 0.80 in 2010 to 2012. This increase in the identification rate was due to an increase in the number of deaths of Aboriginal and Torres Strait Islander people following the introduction of Medical Certificate of Cause of Death (MCCD) in Queensland in 2015. For more information see Quality issues with Aboriginal and Torres Strait Islander deaths and population data.

Using MCCD information only, Queensland identified an extra 163 Aboriginal and Torres Strait Islander deaths: 30, 40 and 93 deaths in 2015, 2016 and 2017 respectively. Of these, only 84 deaths were in-scope for linkage and 70 deaths were successfully linked to a corresponding Census record. The exclusion of 70 linked deaths reduced the identification rate to 0.96 from 1.03.

To produce life tables for the period 2015 to 2017, three-year average deaths, rather than three-year total deaths were used. Therefore, inclusion of 54 (=163 divided by 3) of the 163 deaths identified using MCCD only reduced life expectancy, but this was compensated by adjusting down the registered deaths by the identification rate of 1.03. On balance, including the MCCD only deaths produced exactly the same life expectancy for Aboriginal and Torres Strait Islander males and only 0.1 year higher life expectancy for females compared with those produced by excluding them.

There is quite considerable variation in the identification rates by remoteness (Table 15). The estimates of 0.75 for Major Cities and 0.77 for Inner and Outer Regional areas combined indicates a high level of under-identification of Aboriginal and Torres Strait Islander deaths in death registrations. In contrast, the identification rate of 0.95 for Remote and Very Remote areas combined indicates a much lower level of under-identification.

The following table is used to illustrate the impact on life expectancy at birth when the identification rate is 5% higher or lower than those included in Table 14. The variation is largest for the Northern Territory and Western Australia for both males and females. Life expectancy varies from 65.9 to 67.3 for males and 69.2 to 70.5 for females in the Northern Territory, and from 66.2 to 67.6 for males and 71.2 to 72.4 for females in Western Australia.

The use of the CDE Indigenous Mortality Study to assess the identification rate of Aboriginal and Torres Strait Islander deaths in death registration data has a number of benefits but at the same time it has limitations. First, the obvious and most substantial benefit is that it enables direct calculation of identification rates. That is, they are derived by directly comparing Indigenous status as reported according to death registrations and Census data for linked records, as opposed to indirect and modelled estimates.

Second, no assumptions were necessary to derive the identification rates from the CDE study, whereas a number of subjective judgements and assumptions were necessary to produce identification rates prior to the period from 2005 to 2007.

The limitations of the CDE Indigenous Mortality Study relate to three main factors. First, the derived Aboriginal and Torres Strait Islander deaths identification rates relate to a restricted time frame from 9 August 2016 to 28 September 2017. It is not possible to accurately judge the appropriateness or otherwise of the derived Aboriginal and Torres Strait Islander deaths identification rates for past or future periods.

Second, of the 3,246 Aboriginal and Torres Strait Islander death records eligible for linkage, 931 (28.7%) were not linked to a corresponding Census record. Of all the unlinked records, 23.3% were in New South Wales, 27.1% in Queensland, 19.2% in Western Australia and 17.2% in the Northern Territory. While not unexpected given the relatively high Census undercount for Aboriginal and Torres Strait Islander Australians, there may be features or characteristics of the unlinked records that are quite different to the linked records and therefore may introduce some bias to the results. Sensitivity analysis (see Appendix – Confidence intervals) indicates this is likely to be small.

It should be noted that all unlinked Aboriginal and Torres Strait Islander deaths are included in life tables calculations, but they are excluded from the calculation of identification rates and the resulting adjustment factor that are applied to the life tables. To produce life tables for Aboriginal and Torres Strait Islander Australians, information on the number of Aboriginal and Torres Strait Islander deaths and the Aboriginal and Torres Strait Islander population are required. Data quality issues are discussed in Quality issues with Aboriginal and Torres Strait Islander deaths and population data.

The life tables in this release are based on the average number of Aboriginal and Torres Strait Islander deaths registered in the period from 2015 to 2017 and final Aboriginal and Torres Strait Islander population estimates for 30 June 2016 based on the 2016 Census results. To account for underidentification of Aboriginal and Torres Strait Islander deaths in death registrations, the numbers of Aboriginal and Torres Strait Islander deaths were adjusted according to the adjustment factors derived from the Census Data Enhancement Aboriginal and Torres Strait Islander Mortality Study. This is described in Data linkage to derive Aboriginal and Torres Strait Islander deaths identification rates. The adjusted numbers of Aboriginal and Torres Strait Islander deaths in 2015, 2016 and 2017 were divided by three to obtain the average annual number of Aboriginal and Torres Strait Islander deaths over the period from 2015 to 2017, and in conjunction with 30 June 2016 Aboriginal and Torres Strait Islander population estimates (mid-point of the period from 2015 to 2017) were used to calculate age-specific death rates for the Aboriginal and Torres Strait Islander population.

Third, as stated above, the propensities of Aboriginal and Torres Strait Islander identification as reported in the 2016 Census and 2016 PES are calculated for persons who matched to Census and PES. While PES is a sample representing the whole population, the current methodology implicitly assumes that the propensities based on the Census-PES match will apply for the death registrations linked to the Census. Appendix – Confidence intervals provides some indication of the sensitivity of the estimates of Aboriginal and Torres Strait Islander life expectancy at birth to assumptions made when calculating it.

A further assumption relates to the application of identification rates, which assumed uniformity by age and sex - except for the headline Australia estimate (which used three broad age groups).

In spite of these limitations, the CDE Indigenous Mortality Study clearly shows the need to adjust for underidentification in Aboriginal and Torres Strait Islander death registrations.

On 29 November, 2018 the ABS released the latest official estimates of life expectancy for Aboriginal and Torres Strait Islander peoples. These are the sixth set of life expectancy estimates released by the ABS since the first set was released in 1997.

The latest estimates show that in the period from 2015 to 2017, life expectancy at birth for Aboriginal and Torres Strait Islander men was 71.6 years and 75.6 years for women. This suggests that Aboriginal and Torres Strait Islander men, on average, live 8.6 years less than non-Indigenous men, while Aboriginal and Torres Strait Islander women, on average, live 7.8 years less than non-Indigenous women. This gap has reduced over the last five years by 2.0 years for men and 1.7 years for women. This means, 71.6 is the average number of years that a group of newborn male babies would be expected to live if current death rates remain unchanged. For newborn Aboriginal and Torres Strait Islander female babies, the average number is 75.6 years.

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 older age, life expectancy is only a summary indicator for a population, rather than an exact measure of how long individuals will actually live.

By the time a child reaches their first birthday, their chances of living longer increase (since they have survived their first year). By the time they reach late adulthood, their chances of surviving to a very old age are quite good. For example, although the average life expectancy for Aboriginal and Torres Strait Islander male is 71.6 years, a five year old is expected to live another 67.2 years, making their life expectancy 72.2 years. If an Aboriginal and Torres Strait Islander man reaches age 65, they will have an expected average of 15.8 additional years left to live, making their life expectancy 80.8 years, 9.2 years longer than the average life expectancy at birth.

The latest estimates show that Aboriginal and Torres Strait Islander men born in 2015 to 2017 would live to an average of 71.6 years, while women would live to an average of 75.6 years if current mortality rates continued. However, this does not mean that all or most Aboriginal and Torres Strait Islander people born during 2015 to 2017 will die at or around these ages. These are average values, so some people die before reaching the average life expectancy at birth (including in their first year), while others will live well beyond that age.

Life expectancy is widely used as a key measure of the health of a population. Since life expectancy is expressed in years of life, it is often seen as an indicator that is more easily interpreted than other measures of mortality (e.g. standardised death rates, preventable death rates, etc.). Life expectancy is also not affected by different population age structures, so can be compared across subpopulations, jurisdictions and over time. However, since it’s a summary measure, changes in life expectancy are often much smaller than the changes in other measures. For instance, life expectancy at birth for the population of Australia changed by around 0.3 years of life per year, from 1890 to 2015, despite major changes in infant and child mortality and other mortality trends.

While life expectancy at birth measures how long, on average, a group of people born in the same year can expect to live, it does not take account of how healthy they are expected to be throughout their life. Health adjusted life expectancy estimates are not regularly published, with the most recent data published by the Australian Institute of Health and Welfare in: Australian Burden of Disease Study: impact and causes of illness and death in Aboriginal and Torres Strait Islander people, 2011.

Life expectancy is calculated using life tables, which bring together deaths data and population estimates. By temporarily linking death registration records and Census records, the ABS is able to confirm that there are a number of deaths of Aboriginal and Torres Strait Islander people which are not identified as such on their death registration. From this the ABS is able to estimate how many deaths there would have been in the Aboriginal and Torres Strait Islander population, had all of the people who died been identified as they were in the Census. This method, known as the 'direct method', was first used by the ABS for Aboriginal and Torres Strait Islander life expectancy for the period from 2005 to 2007. The estimates produced by this method are considered to be more accurate than those from the previous method (the 'indirect method', which required the ABS to make a range of assumptions in the calculation).

For the period from 2015 to 2017 estimates the ABS again used the 'direct method'.

We thank Australian Aboriginal and Torres Strait Islander peoples for their cooperation and assistance in the collection of data, without whom this analysis would not have been possible.

The ABS would like to recognise the valuable contribution made by key experts to the methods used by the ABS. In particular, the Aboriginal and Torres Strait Islander Demographic Statistics Expert Advisory Group has provided invaluable advice to the ABS in the lead-up to producing the 2015 to 2017 estimates.

This release previously used catalogue number 3302.0.55.003.