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# Life Tables for Aboriginal and Torres Strait Islander Australians methodology

Reference period
2015 - 2017
Released
29/11/2018
Next release Unknown
First release

## Explanatory notes

### Introduction

1 The life tables in this release are based on the average number of Aboriginal and Torres Strait Islander deaths registered in 2015-2017 adjusted for under/over identification of Indigenous Status in registrations, and final Aboriginal and Torres Strait Islander population estimates for 30 June 2016 based on the 2016 Census (mid-point between the 2015-2017 reference year).

### Use of Aboriginal and Torres Strait Islander life tables

2 Estimates of life expectancy at birth for Aboriginal and Torres Strait Islander Australians are commonly used as a measure for assessing Aboriginal and Torres Strait Islander population health and disadvantage.

3 The life tables in this release will also enable the construction of ABS estimates and projections of the Aboriginal and Torres Strait Islander Australians for the period 2006 to 2031. These data are produced using the cohort-component method, in which assumptions made about levels of mortality, fertility and migration are iteratively applied to a base population to obtain past and/or future populations.

### Scope

4 Life tables in this release relate to the resident populations of New South Wales, Queensland, Western Australia, Northern Territory and Australia (which includes all states and territories). Due to the small number of Aboriginal and Torres Strait Islander deaths in Victoria, South Australia, Tasmania and the Australian Capital Territory, it is not possible to construct separate reliable life tables for these jurisdictions (see paragraphs 22-23).

### Indigenous status

5 ABS Aboriginal and Torres Strait Islander population statistics are based on responses to the ABS standard question for Indigenous identification (Question 7 in the 2016 Census), as below:

Text description for

Question text: Is the person of Aboriginal or Torres Strait Islander Origin?

Question instructions: For persons of both Aboriginal and Torres Strait Islander origin, mark both "Yes" boxes.

Question response categories:

No
Yes, Aboriginal
Yes, Torres Strait Islander

### Remoteness Structure

6 The Remoteness Structure divides each state and territory into several regions on the basis of their relative access to services. Remoteness Areas (RA) are the spatial units that make up the Australian Statistical Geography Standard (ASGS) Remoteness Structure. There are six classes of Remoteness Area in the Remoteness Structure: Major Cities of Australia, Inner Regional Australia, Outer Regional Australia, Remote Australia, Very Remote Australia and Migratory.

7 Within a state/territory, each RA represents an aggregation of non-contiguous geographical areas which share common characteristics of remoteness.

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

9 For further information see Australian Statistical Geography Standard (ASGS): Volume 5 - Remoteness Structure, July 2016 (cat. no. 1270.0.55.005).

### Method for producing life tables

10 A life table is a statistical model used to represent mortality of a population. In its simplest form, a life table is generated from age-specific death rates and the resulting values are used to measure mortality, survivorship and life expectancy.

11 A life table may be complete or abridged, depending on the age intervals used in their compilation. Life tables in this release are abridged life tables - they contain data for five-year age groups - and are presented separately for males and females. Abridged life tables were chosen as age-specific death rates for five-year age groups were considered more reliable than those for single years of age due to the small annual numbers of Aboriginal and Torres Strait Islander deaths in the states and territories.

12 To construct a life table, data on deaths that occur in a period and estimates of the population (at the mid-point of the period) exposed to the risk of dying are required, disaggregated by age and sex.

13 The first step in the compilation of a life table involves the calculation of age-specific death rates (ASDRs) for the population of interest. ASDRs are calculated as:

• ASDR $$_{a,s}$$= Deaths$$_{a,s}$$ / Populationa$$_{a,s}$$ where

• ASDR$$_{a,s}$$ is the age-specific death rate for age group a and sex s;
• Deaths$$_{a,s}$$ is the number of deaths for age group a and sex s over the specified period of time; and
• Population$$_{a,s}$$ is the population of the age group a and sex s at the mid-point of the specified period.

14 The next step is to derive mortality rates (the proportion of people of a given age who die within one year, denoted by qx) from ASDRs. The mortality rates are then applied to a hypothetical group of newborn babies (typically 100,000 in size) until the population has died out. This results in a range of related functions, of which the life tables in this release include:

• lx - the number of persons surviving to exact age x;
• qx - the proportion of persons dying between exact age x and exact age x+n (where n is the width of the age interval). It is the mortality rate, from which all other functions of the life table are derived;
• Lx - the number of person years lived within the age interval x to x+n; and
• ex - life expectancy at exact age x.

15 The life tables in this release are abridged life tables, based on the average number of Aboriginal and Torres Strait Islander deaths registered in 2015-2017 and final Aboriginal and Torres Strait Islander population estimates for 30 June 2016 based on the 2016 Census results (mid-point between the 2015-2017 reference year). Abridged life tables assume that as a group of new-born babies pass through life it will experience the mortality rates of the specific period which do not change from year to year. Period life tables thus constitute a hypothetical model of mortality, and, although based upon mortality rates from a real population during a particular period of time, do not describe the future mortality of this group.

### Life tables for the non-Indigenous population

16 Life tables for the non-Indigenous population were produced to enable a comparison of life expectancy at birth and other ages between the Aboriginal and Torres Strait Islander and non-Indigenous populations of Australia.

17 Numbers of non-Indigenous deaths were obtained by subtracting the adjusted average number of Aboriginal and Torres Strait Islander deaths in 2015-2017 from the total number of deaths registered in 2015-2017 and dividing by three to obtain the average annual number of non-Indigenous deaths.

18 Final estimates of the non-Indigenous population for 30 June 2016 from Estimates of Aboriginal and Torres Strait Islander Australians, Jun 2016 (cat. no. 3238.0.55.001) were used as denominators in the calculation of age-specific death rates for the non-Indigenous population, and life tables derived from these.

19 Graduation refers to a standard demographic technique of smoothing to remove the effect of year to year volatility in numbers of deaths (by age and sex) on mortality rates (qx). This ensures that implausible results do not occur in the life tables, such as female mortality rates exceeding male mortality rates.

20 Life tables were first produced for the Aboriginal and Torres Strait Islander and non-Indigenous populations as described above. While numbers of deaths were averaged for 2015-2017, the resulting mortality rates still contained some volatility across age groups. Mortality rates were therefore adjusted so that the rates were smooth across age groups. This was done for both Aboriginal and Torres Strait Islander and non-Indigenous life tables, for all states and territories and both sexes.

21 The graduation of life tables was performed so that life expectancy at birth estimates were unaffected, but minor changes to life expectancy at other ages occurred.

### Victoria, South Australia, Tasmania and Australian Capital Territory

22 The compilation of life tables requires sufficient numbers of deaths to allow the calculation of reliable ASDRs for each age group. With small numbers of deaths the resulting ASDRs are likely to be volatile, and, particularly at younger ages, may be zero.

23 Due to the small Aboriginal and Torres Strait Islander populations of Victoria, South Australia, Tasmania and the Australian Capital Territory, these jurisdictions record very small numbers of Aboriginal and Torres Strait Islander deaths annually (around 167, 186, 52 and 19 Aboriginal and Torres Strait Islander deaths per year on average for 2015-2017 respectively). Disaggregating the numbers of Aboriginal and Torres Strait Islander deaths in these jurisdictions by 5 year age groups to 85 years and over and by sex results in extremely small numbers of deaths for any age group and sex, from which it is not possible to calculate reliable age-specific death rates. For this reason it is not possible to produce reliable life tables for the Aboriginal and Torres Strait Islander populations of these jurisdictions.

### Life expectancy in Deaths, Australia (cat. no. 3302.0)

24 Estimates of life expectancy at birth for the total population presented in this release differ from estimates published in Life Tables, States, Territories and Australia, 2015-2017 (cat. no. 3302.0.55.001). Estimates presented in this release are derived from abridged life tables with an upper age limit of 85 years and over, using adjusted numbers of deaths registered in 2015-2017 and the population as at 30 June 2016, while life expectancy estimates in Life Tables, States, Territories and Australia, 2015-2017 (cat. no. 3302.0.55.001) are based on complete life tables with an upper age group of 120 years and over, using deaths according to month of occurrence in 2015-2017 and quarterly population estimates. In addition, graduation processes applied to both sets of life tables differ.

### Life expectancy by Index of Relative Socio-Economic Disadvantage (IRSD)

25 Life expectancy at birth estimates by the Index of Relative Socio-Economic Disadvantage (IRSD) are presented in Chapter 1: Life expectancy at Birth. These estimates have been produced using the same methodology as for states/territory, Australia and remoteness areas.

### Confidentiality

26 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.

27 Where necessary, tables in this release have had small values suppressed or randomised to protect confidentiality. As a result, sums of components may not add exactly to totals.

### Rounding

28 Calculations as shown in the commentary sections of this release are based on unrounded figures. Calculations using rounded figures may differ from those released. Where figures have been rounded in tables, discrepancies may occur between sums of component items and totals.

30 The abridged life tables in chapter 4 are also available as a data cube (in Microsoft Excel format) available for download from the ABS website in Life Tables for Aboriginal and Torres Strait Islander Australians, 2015-2017 (cat. no. 3302.0.55.003):

• Table 1: Life Tables for Aboriginal and Torres Strait Islander Australians, Selected States and Territory and Australia - 2015-2017
• Table 2: Life Tables for Aboriginal and Torres Strait Islander Australians, Remoteness Areas, Australia - 2015-2017
• Table 3: Life Tables for Aboriginal and Torres Strait Islander Australians, Index of Relative Socio-Economic Disadvantage, Australia - 2015-2017
• Table 4: Summary of Linked Deaths by Indigenous Status, Deaths Registrations and Census Identification, Selected States and Territory and Australia - 2016-2017
• Table 5: Summary of Linked Deaths by Indigenous Status, Deaths Registrations and Census Identification, Remoteness Areas, Australia - 2016-2017
• Table 6: Summary of Linked Deaths by Indigenous Status, Deaths Registrations and Census Identification, Index of Relative Socio-Economic Disadvantage, Australia - 2016-2017
• Table 7: Difference in Indigenous classification between Census and PES identification, Unweighted and Weighted data, Selected States and Territory and Australia - 2016
• Table 8: Difference in Indigenous classification between Census and PES identification, Unweighted and Weighted data, Remoteness Areas, Australia - 2016
• Table 9: Difference in Indigenous classification between Census and PES identification, Unweighted and Weighted data, Index of Relative Socio-Economic Disadvantage, Australia - 2016

31 Additional demographic information is available on the ABS website http://www.abs.gov.au; click Statistics, then under People click on Aboriginal and Torres Strait Islander Peoples. Users can also access the full range of electronic ABS data from the ABS website.

32 As well as the statistics included in this and related releases, 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.

33 The ABS also issues a daily Release Advice on the website which details the products to be released in the week ahead.

## Appendix - confidence intervals

### Show all

#### Estimating sample error

This appendix describes the basis for estimating the sample error of estimates of Aboriginal and Torres Strait Islander life expectancy at birth and for assessing the sensitivity of this life expectancy to assumptions made when calculating it. Broadly, a process of replication was used where the inputs to the Aboriginal and Torres Strait Islander life expectancy calculations were replicated based on sample error information obtained from the Post Enumeration Survey (PES) and on plausible deviations from the assumptions. Variation between the replicate estimates of Aboriginal and Torres Strait Islander life expectancy corresponding to replicate estimates from PES gave estimates of the sample error of life expectancy and the additional variation from deviations from the assumptions measured the sensitivity of the method to the assumptions.

The immediate inputs to Aboriginal and Torres Strait Islander life expectancy are:

• Aboriginal and Torres Strait Islander estimated resident population (ERP) at 30 June 2016 (mid-point between the 2015-2017 reference period) by five-year age groups; and
• Average number of Aboriginal and Torres Strait Islander deaths over the 2015-2017 reference period, adjusted for differences in reporting Indigenous status.

The method of calculating Aboriginal and Torres Strait Islander ERP is described in Estimates of Aboriginal and Torres Strait Islander Australians, June 2016 (cat. no. 3238.0.55.001). The method of adjusting Aboriginal and Torres Strait Islander deaths for differential identification is given in Chapter 3: Data linkage to derive Aboriginal and Torres Strait Islander deaths identification rates.

The inputs to the calculation of Aboriginal and Torres Strait Islander ERP are:

• Census counts at fine levels;
• estimates of total population (both Aboriginal and Torres Strait Islander and non-Indigenous) at intermediate levels; and
• estimates of Aboriginal and Torres Strait Islander population at broad levels.

The main input for adjusted Aboriginal and Torres Strait Islander deaths are Aboriginal and Torres Strait Islander deaths registered during 2015-2017, modified using the Aboriginal and Torres Strait Islander deaths identification rate. This adjusts the Indigenous status of death registrations to correspond to the Indigenous status in ERP, which is as reported in PES. The identification rate is calculated from a probabilistic linking of death registrations between 9 August 2016 and 28 September 2017 to the 2016 Census and from PES data.

Other inputs are:

• number of deaths in linked records reported as Aboriginal and Torres Strait Islander in death registrations, by age groups, state/territory and remoteness, and
• number of deaths in linked records by Census Indigenous status, by state/territory and age groups;

From these inputs, the following propensities were calculated:

• propensity of being Aboriginal and Torres Strait Islander in PES given Census Indigenous status is 'Aboriginal and Torres Strait Islander', by state/territory and age groups; and
• propensities of being Aboriginal and Torres Strait Islander in PES given Census Indigenous status is 'non-Indigenous' and 'not stated' by age groups.

Estimates of the total and Aboriginal and Torres Strait Islander populations incorporate components of PES undercount adjustment and the propensities are calculated from PES, and so the sample error in PES generates sample error in Aboriginal and Torres Strait Islander life expectancy. Standard errors (SEs) were calculated by replication of PES inputs, based on estimated PES sampling error.

Note that PES data are weighted to estimate the propensities but unweighted data were used to illustrate the methodology in Chapter 3: Data linkage to derive Aboriginal and Torres Strait Islander deaths identification rates.

#### Estimating sensitivity error

In calculating and applying the identification rate the following assumptions were made:

• identification rates for unlinked deaths were assumed to be the same as those for linked deaths;
• identification rates for 2015-2017 were assumed to be the same as those observed for August 2016 to September 2017;
• identification rates were assumed to apply uniformly across sex and within each broad age group;
• propensities for Aboriginal and Torres Strait Islander identification in the Census and PES were assumed to be applicable to death registrations, in spite of the different age distributions and method of collection; and
• Census/PES non-Indigenous and not stated propensities for Australia were assumed to apply uniformly across states/territories.

There was no direct information on possible deviation from the first two assumptions, but deviations within plus or minus five percentage points of identification rate for each state were used for the first assumption, and within plus or minus two percentage points for each sex and state for the second assumption. Data from the linked file and PES were analysed to give ranges of deviations in identification rates for the last three assumptions.

#### Results

The 95% confidence intervals for Aboriginal and Torres Strait Islander life expectancy at birth estimates from the sensitivity analysis and sample error are given in Table A1.1, Table A1.2 and Table A1.3 below.

#### A1.1 Confidence intervals for Aboriginal and Torres Strait Islander life expectancy at birth - 2010-2012(a) and 2015-2017(b)

95% CONFIDENCE INTERVALS
State/TerritoryMalesFemalesMalesFemales
New South Wales
2010-2012
70.5 [69.0—72.0]
74.6 [73.3—75.9]
70.5 [69.8—71.2]
74.6 [74.0—75.2]
2015-2017
70.9 [68.8—73.0]
75.9 [74.3—77.6]
70.9 [69.8—72.0]
75.9 [75.1—76.8]
Queensland
2010-2012
68.7 [67.3—70.1]
74.4 [73.2—75.6]
68.7 [68.0—69.4]
74.4 [73.9—74.9]
2015-2017
(d)72.0 [70.3—73.7]
76.4 [75.0—77.9]
(d)72.0 [70.9—73.2]
(d)76.4 [75.5—77.4]
Western Australia
2010-2012
65.0 [63.4—66.6]
70.2 [68.8—71.6]
65.0 [ 64.1—65.9]
70.2 [69.4—71.0]
2015-2017
66.9 [65.0—68.8]
71.8 [70.1—73.5]
66.9 [ 65.4—68.4]
71.8 [70.4—73.1]
Northern Territory
2010-2012
63.4 [61.3—65.5]
68.7 [66.8—70.6]
63.4 [ 62.4—64.4 ]
68.7 [ 67.8—69.6]
2015-2017
66.6 [65.4—67.8]
69.9 [68.8—70.9]
(d)66.6 [ 65.7—67.5 ]
69.9 [ 69.0—70.7]
Australia for comparison(e)
2010-2012
67.4 [66.1—68.7]
72.3 [71.2—73.4]
67.4 [67.1—67.7]
72.3 [72.0—72.6]
2015-2017
(d)70.0 [68.8—71.1]
(d)74.4 [73.5—75.4]
(d)70.0 [69.3—70.6]
(d)74.4 [73.9—74.9]
2010-2012
69.1 [67.8—70.4]
73.7 [72.5—74.9]
69.1 [68.8—69.4]
73.7 [ 73.4—74.0]
2015-2017
71.6 [70.0—73.2]
75.6 [74.3—76.9]
(d)71.6 [70.9—72.3]
(d)75.6 [75.0—76.3]
a. Based on the average number of Aboriginal and Torres Strait Islander deaths registered in 2010-2012 adjusted for under/over identification of Indigenous Status in registrations, and final Aboriginal and Torres Strait Islander population estimates for 30 June 2011 based on the 2011 Census.
b. Based on the average number of Aboriginal and Torres Strait Islander deaths registered in 2015-2017 adjusted for under/over identification of Indigenous Status in registrations, and final Aboriginal and Torres Strait Islander population estimates for 30 June 2016 based on the 2016 Census.
c. Sensitivity to assumptions, includes sample error.
d. Significantly different from 2010-2012 estimate at 95% confidence level.
e. These life expectancy estimates are calculated without taking age-specific identification rates into account.
f. Includes all states and territory.
g. These life expectancy estimates are calculated taking age-specific identification rates into account.

#### A1.2 Confidence intervals for Aboriginal and Torres Strait Islander life expectancy at birth, Remoteness Areas - 2015-2017(a)

95% CONFIDENCE INTERVALS
Remoteness AreasMalesFemalesMalesFemales
Major Cities
72.1 [70.4—73.7]
76.5 [75.2—77.8]
72.1 [70.8—73.4]
76.5 [75.5—77.5]
Inner and Outer Regional
70.0 [68.5—71.5]
74.8 [73.6—76.1]
70.0 [68.7—71.3]
74.8 [73.8—75.9]
Remote and Very Remote
65.9 [64.7—67.1]
69.6 [68.5—70.8]
65.9 [65.0—66.8]
69.6 [68.8—70.5]
a. Based on the average number of Aboriginal and Torres Strait Islander deaths registered in 2015-2017 adjusted for under/over identification of Indigenous Status in registrations, and final Aboriginal and Torres Strait Islander population estimates for 30 June 2016 based on the 2016 Census.
b. Sensitivity to assumptions, includes sample error.

#### A1.3 Confidence intervals for Aboriginal and Torres Strait Islander life expectancy at birth, Index of Relative Socio-Economic Status (SEIFA) - 2015-2017(a)

95% CONFIDENCE INTERVALS
SEIFA AreasMalesFemalesMalesFemales
68.2 [67.6—68.8]
72.8 [72.3—73.3]
68.2 [67.4—68.9]
72.8 [72.1—73.4]
70.3 [69.5—71.1]
75.5 [74.9—76.1]
70.3 [69.3—71.4]
75.5 [74.7—76.4]
Middle 20%
69.9 [68.9—70.9]
74.3 [73.5—75.1]
65.9 [68.5—71.3]
74.3 [73.1—75.5]
72.4 [71.3—73.5]
76.6 [75.6—77.6]
72.4 [71.0—73.8]
76.6 [75.4—77.8]
a. Based on the average number of Aboriginal and Torres Strait Islander deaths registered in 2015-2017 adjusted for under/over identification of Indigenous Status in registrations, and final Aboriginal and Torres Strait Islander population estimates for 30 June 2016 based on the 2016 Census.
b. Sensitivity to assumptions, includes sample error.

The 95% confidence intervals for Aboriginal and Torres Strait Islander death identification rates from the sensitivity analysis and sample error are given in Table A1.4, Table A1.5 and Table A1.6 below.

#### A1.4 Confidence intervals for Aboriginal and Torres Strait Islander deaths indentification rates - 2015-2017(a)

95% CONFIDENCE INTERVALS
Identification rateSensitivity error(b)Sample error
State/territoryno.no.no.
NSW
0.69
0.58-0.79
0.64-0.74
Qld
1.03
0.89-1.16
0.95-1.10
WA
0.94
0.85-1.03
0.88-1.00
NT
1.04
0.98-1.10
1.03-1.05
Aust.(c)(d)
0.80
0.73-0.87
0.77-0.83
0.92
0.81-1.04
0.86-0.98
a. Based on the average number of Aboriginal and Torres Strait Islander deaths registered in 2015-2017 adjusted for under/over identification of Indigenous Status in registrations, and final Aboriginal and Torres Strait Islander population estimates for 30 June 2016 based on the 2016 Census.
b. Sensitivity to assumptions. Includes sample error.
c. These life expectancy estimates are calculated without taking age-specific identification rates into account.
d. This identification rate is included for comparison purposes only. Refer to table 3.5 for age-specific identification rates.
e. Includes all states and territories.
f. These life expectancy estimates are calculated taking age-specific identification rates into account.

#### A1.5 Confidence intervals for Aboriginal and Torres Strait Islander death identification rates, Remoteness Areas - 2015-2017(a)

95% CONFIDENCE INTERVALS
Identification rateSensitivity error(b)Sample error
Remoteness Areano.no.no.
Major Cities
0.75
0.65-0.85
0.68-0.83
Inner and Outer Regional
0.77
0.68-0.85
0.69-0.84
Remote and Very Remote
0.95
0.88-1.03
0.90-1.01
a. Based on the average number of Aboriginal and Torres Strait Islander deaths registered in 2015-2017 adjusted for under/over identification of Indigenous Status in registrations, and final Aboriginal and Torres Strait Islander population estimates for 30 June 2016 based on the 2016 Census.
b. Sensitivity to assumptions, includes sample error.

#### A1.6 Confidence intervals for Aboriginal and Torres Strait Islander death identification rates, Index of Relative Socio-Economic Status (SEIFA) - 2015-2017(a)

95% CONFIDENCE INTERVALS
Identification rateSensitivity error(b)Sample error
Remoteness Areano.no.no.
0.88
0.81-0.95
0.84-0.92
0.80
0.71-0.89
0.75-0.86
Middle 20%
0.76
0.65-0.87
0.68-0.83
0.60
0.48-0.72
0.53-0.67
a. Based on the average number of Aboriginal and Torres Strait Islander deaths registered in 2015-2017 adjusted for under/over identification of Indigenous Status in registrations, and final Aboriginal and Torres Strait Islander population estimates for 30 June 2016 based on the 2016 Census.
b. Sensitivity to assumptions, includes sample error.

## Appendix - alternative approaches to adjust deaths

### Show all

#### Introduction

In Life Tables for Aboriginal and Torres Strait Islander Australians, 2010-2012 (cat. no. 3302.0.55.003) the ABS presented four alternative approaches for adjusting deaths data as an input to compilation of life tables. While not the best method each of these approaches does provide useful insights into the official method and adds particular value. These four methods have been included for 2015-2017.

#### Alternative approaches to adjust deaths

The four alternative approaches for which illustrative estimates were produced were

1. using deaths identified as Aboriginal and Torres Strait Islander in death registrations without any adjustment;
2. using deaths identified as Aboriginal and Torres Strait Islander in either the Census or death registrations in the CDE linked data only;
3. using deaths identified as Aboriginal and Torres Strait Islander in either the Census or death registrations in the CDE linked and unlinked data; and
4. using Aboriginal and Torres Strait Islander identification based on the 2016 Census.

The first approach shows what life expectancy would have been if no adjustment was made for the underidentification of Indigenous status in deaths registration data.

The second and third approaches are provided here as approaches that were explored by the ABS for the 2005-2007 and 2010-2012 estimates but were considered to be unsuitable for estimating Aboriginal and Torres Strait Islander mortality. The main reason for this is that the identification of Indigenous status in the numerator (deaths) and the denominator (population estimates) are not consistent with each other, thus introducing bias to life expectancy estimates.

The fourth approach was also explored by the ABS, but the resultant life expectancy at birth estimates were considerably higher than the other estimates and not considered to be plausible.

A brief discussion of each of the different approaches and the results obtained are presented below.

#### 1. Deaths identified as Aboriginal and Torres Strait Islander in death registrations without any adjustment

This method produces life expectancy estimates based on no adjustment made to the number of Aboriginal and Torres Strait Islander deaths to account for underidentification. This shows that no adjustment to the number of deaths leads to higher life expectancy for New South Wales and Western Australia, and slightly lower life expectancy for Queensland and the Northern Territory females.

#### A2.1 Aboriginal and Torres Strait Islander life expectancy at birth, based on unadjusted death registrations - 2015-2017(a)

MalesFemales
State/territoryyearsyears
NSW
75.3
79.4
Qld
71.7
76.2
WA
67.8
72.5
NT
66.1
69.3
Aust.(b)
72.6
76.5
a. Based on the average number of unadjusted Aboriginal and Torres Strait Islander deaths registered in 2015-2017, and final Aboriginal and Torres Strait Islander population estimates for 30 June 2016 based on the 2016 Census.
b. Includes all states and territories.

#### 2. Deaths identified as Aboriginal and Torres Strait Islander in either Census or death registrations in the CDE linked data only

For the 2005-2007 and 2010-2012 estimates, ABS explored an option to derive identification rates for Aboriginal and Torres Strait Islander deaths and life expectancy estimates using the CDE linked data only.

This approach uses a concept of Indigenous status which is different from that used for the denominator for death rates; that is, population estimates where Indigenous status is as reported in PES only but not augmented by other sources of information. In calculating life expectancy estimates, it is important to ensure that the classification of records as Aboriginal and Torres Strait Islander occurs in a consistent manner in the numerator (deaths) and the denominator (population estimates) as different population scopes feed directly into bias in death rates.

#### A2.2 CDE linked data(a), identification rates and life expectancy estimates based on Aboriginal and Torres Strait Islander deaths - 2015-2017(b)

LIFE EXPECTANCY AT BIRTH
Aboriginal and Torres Strait Islander deaths in death registrationsAdditional Aboriginal and Torres Strait Islander deaths identified in Census onlyTotal Aboriginal and Torres Strait Islander deaths by deaths registrations or CensusAboriginal and Torres Strait Islander deaths identification rate(c)MalesFemales
State/territoryno.no.no.no.yearsyears
NSW
689
332
1,021
0.67
70.7
75.8
Qld
654
114
768
0.85
69.7
74.5
WA
353
41
394
0.90
66.2
71.2
NT
277
8
285
0.97
65.7
68.9
Aust.(d)
2,315
726
3,041
0.76
69.1
73.6
a. Deaths identified in either Census or registration in the CDE linked data.
b. Final Aboriginal and Torres Strait Islander population estimates for 30 June 2016 based on the 2016 Census.
c. Ratio of Aboriginal and Torres Strait Islander deaths identified in death registrations to the total Aboriginal and Torres Strait Islander deaths identified in either registration and Census.
d. Includes all states and territories.

#### 3. Deaths identified as Aboriginal and Torres Strait Islander in either Census or death registrations in the CDE linked and unlinked data

This approach, like the previous approach, is based on Aboriginal and Torres Strait Islander deaths identified in either the Census or death registrations, but uses the Aboriginal and Torres Strait Islander deaths identified in the CDE linked file plus those Aboriginal and Torres Strait Islander deaths which were unable to be linked to a Census record.

#### A2.3 CDE linked and unlinked data(a), identification rates and life expectancy estimates based on Aboriginal and Torres Strait Islander deaths - 2015-2017(b)

LIFE EXPECTANCY AT BIRTH ESTIMATES
Aboriginal and Torres Strait Islander deaths from death registrations prior to linkageAboriginal and Torres Strait Islander deaths after linkageAboriginal and Torres Strait Islander deaths identification rate(c)MalesFemales
State/territoryno.no.no.yearsyears
NSW
906
1,238
0.73
71.7
76.6
Qld
906
1,020
0.89
70.3
74.9
WA
532
573
0.93
66.7
71.6
NT
437
445
0.98
65.8
69.1
Aust.(d)
3,246
3,972
0.82
70.1
74.4
a. Deaths identified in either Census or registration in the CDE linked and unlinked data.
b. Final Aboriginal and Torres Strait Islander population estimates for 30 June 2016 based on the 2016 Census.
c. Ratio of Aboriginal and Torres Strait Islander deaths prior to linkage to Aboriginal and Torres Strait Islander deaths after linkage.
d. Includes all states and territories.

Like the previous approach, this approach also produces life expectancy estimates which are biased as the identification of Indigenous status in the numerator and the denominator are inconsistent.

#### 4. Direct method using identification based on the 2016 Census

The CDE linked dataset can be used to derive direct estimates of mortality of the Aboriginal and Torres Strait Islander population counted in the 2016 Census. The method of estimation involves a three stage process. Firstly, people who identified themselves as Aboriginal and Torres Strait Islander in the 2016 Census were selected from the Census. Secondly, only those death records for which Indigenous status was reported as Aboriginal and Torres Strait Islander in the Census were taken from the linked file. Thirdly, age-specific death rates were calculated by dividing the Aboriginal and Torres Strait Islander deaths by the Aboriginal and Torres Strait Islander Census counts. These rates were then used to derive Aboriginal and Torres Strait Islander life tables. No adjustments were made to the death rates to account for potential undercoverage of deaths, hence the method is referred to as 'direct'.

This approach was intended to make Aboriginal and Torres Strait Islander counts for deaths and for the population at risk (that is, Aboriginal and Torres Strait Islander usual residents of Australians) consistent. However, this is not the case. Due to undercount in Census a proportion of death records could not be linked, as there was no corresponding Census record to link with. Such people are removed from the counts of deaths and from the counts of the population at risk. However, people whose information from death registrations or Census is not accurate enough to make a link are not included in the death counts, but it is not possible to remove from the Census count the corresponding count of people with unlinkable information in Census or what would have been unlinkable information from death registrations, had they died.

## Glossary

### Show all

#### Aboriginal and Torres Strait Islander death

The life tables in this release are based on the average number of Aboriginal and Torres Strait Islander deaths registered in 2015-2017 adjusted for under/over identification of Indigenous Status in registrations.

Death registrations are collected in the form of administrative data from the Registrars of Births, Deaths and Marriages in each state/territory. For all states and territories, death registration forms (DRFs) use a standard question to elicit information about a person's Aboriginal and Torres Strait Islander origin. The death of a person is recorded as Aboriginal, Torres Strait Islander or both on the Death Registration Form (DRF). From 2007, Indigenous status for deaths registered in South Australia, Western Australia, Tasmania, the Northern Territory and the Australian Capital Territory was also derived from the Medical Certificate of Cause of Death (MCCD). The Queensland Registry of Births, Deaths and Marriages introduced the MCCD in 2015.

#### Aboriginal and Torres Strait Islander Estimated Resident Population (ERP)

The population used in this release is the final Aboriginal and Torres Strait Islander population estimates for 30 June 2016 based on the 2016 Census. For information on the method of calculating the Aboriginal and Torres Strait Islander estimated resident population, see: Technical Note 1 Estimated Resident Aboriginal and Torres Strait Islander Population - Method of calculation in the publication: Estimates of Aboriginal and Torres Strait Islander Australians, June 2016 (cat. no. 3238.0.55.001).

#### Age-specific death rates

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

#### Census

The complete enumeration of a population or groups at a point in time with respect to well-defined characteristics (eg Population, Manufacturing, etc.). In this release the word "Census" refers to the ABS Census of Population and Housing.

#### Confidence intervals

A confidence interval is a range of values that is used to describe the uncertainty around an estimate, usually from a sample survey. Confidence intervals describe how different the estimate could have been if a different sample was selected from the population. Confidence intervals are calculated with a stated probability (commonly 95%). This means that there is a 95% chance that the true population value will lie within the particular range.

#### Death

The permanent disappearance of all evidence of life after birth has taken place. The definition excludes deaths prior to live birth. For the purposes of the ABS Death Registration collection, a death refers to any death which occurs in, or en route to Australia and is registered with a state or territory Registry of Births, Deaths and Marriages.

#### Estimated Resident Population (ERP)

The official measure of the population of Australia is based on the concept of usual residence. It refers to all people, regardless of nationality, citizenship or legal status, who usually live in Australia, with the exception of foreign diplomatic personnel and their families. It includes usual residents who are overseas for less than 12 months over a 16 month period. It excludes overseas visitors who are in Australia for less than 12 months over a 16 month period.

Estimates of the Australian resident population are generated on a quarterly basis by adding natural increase (the excess of births over deaths) and net overseas migration (NOM) occurring during the period to the population at the beginning of each period.

#### Identification rate

The ratio of observed to expected deaths.

#### Imputation

A statistical process for predicting values where no response was provided to a question and a response could not be derived.

#### Index of Relative Socio-Economic Disadvantage (IRSD)

The Index of Relative Socio-Economic Disadvantage (IRSD) used in this release was developed by the ABS and ranks areas in Australia according to most disadvantaged to least disadvantaged using variables from the 2016 Census of Population and Housing. A low score on this index indicates a high proportion of relatively disadvantaged people in an area. It cannot be concluded that an area with a very high score has a large proportion of relatively advantaged people, as there are no variables in the index to indicate this.

#### Life expectancy

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

#### Life table

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

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

#### Natural increase

Excess of births over deaths.

#### Net undercount

The difference between the actual Census count (including imputations) and an estimate of the number of people who should have been counted in the Census. This estimate is based on the Post Enumeration Survey (PES) conducted after each Census. For a category of person (e.g. based on age, sex and state of usual residence), net undercount is the resultant of Census undercount, overcount, misclassification and imputation error.

#### Non-sampling error

Error which arises from inaccuracies in collecting, recording and processing the data. Every effort is made to minimise non-sampling error by the careful design of questionnaires, intensive training and supervision of interviewers, and efficient data processing procedures. Non-sampling error also arises because information cannot be obtained from all people selected in the collection.

#### Other territories

Following the 1992 amendments to the Acts Interpretation Act to include the Indian Ocean Territories of Christmas Island and the Cocos (Keeling) Islands as part of geographic Australia, another category of the state and territory level has been created, known as Other Territories. Other Territories include Norfolk Island, Jervis Bay, Christmas Island, and the Cocos (Keeling) Islands.

#### Post Enumeration Survey (PES)

A household survey conducted three to four weeks after the Census. The PES allows the ABS to estimate the number of people who should have been counted in the Census compared to the number who were. Results from the PES contribute to a more accurate calculation of the estimated resident population (ERP) for Australia and the states and territories which is then backdated to 30 June of the Census year.

#### Sampling error

Error which occurs because a sample, rather than the entire population, is surveyed. One measure of the likely difference resulting from not including all dwellings in the survey is given by the standard error.

#### SEIFA

Socio-Economic Indexes for Areas (SEIFA) is a product developed by the ABS that ranks areas in Australia according to relative socio-economic advantage and disadvantage. The indexes are based on information from the five-yearly Census.

SEIFA 2016 is the latest version of this product and consists of four indexes:

• The Index of Relative Socio-Economic Disadvantage (IRSD)
• The Index of Education and Occupation (IEO)
• The Index of Economic Resources (IER).

Each index is a summary of a different subset of Census variables and focuses on a different aspect of socio-economic advantage and disadvantage.

#### Standard error

A measure of the spread of the difference between the Census value and an estimate. There are about two chances in three that a sample estimate will differ by less than one standard error from the figure that would have been obtained from a Census, and about nineteen chances in twenty that the difference will be less than two standard errors.

#### Unexplained growth

The intercensal growth in the Indigenous population counts that cannot be fully explained by births, deaths and migration.

#### Year of occurrence

The year the death occurred.

#### Year of registration

The year the death was registered.

## Bibliography

### Show all

Australian Bureau of Statistics, Census of Population and Housing - Details of Undercount, 2016, cat. no. 2940.0, ABS, Canberra.

Australian Bureau of Statistics, Census of Population and Housing: Understanding the Increase in Aboriginal and Torres Strait islander Counts, 2016, cat. no. 2077.0, ABS, Canberra.

Australian Bureau of Statistics, Births, Australia, cat. no. 3301.0, ABS, Canberra.

Australian Bureau of Statistics, Deaths, Australia, cat. no. 3302.0, ABS, Canberra.

Australian Bureau of Statistics, Estimates and Projections, Aboriginal and Torres Strait Islander Australians, 2001 to 2026, cat. no. 3238.0, ABS, Canberra.

Australian Bureau of Statistics, Estimates of Aboriginal and Torres Strait Islander Australians, Jun 2016, cat. no. 3238.0.55.001, ABS, Canberra.

Australian Bureau of Statistics, Information Paper: Death registrations to Census linkage project - Key Findings for Aboriginal and Torres Strait Islander peoples, 2011-2012, cat. no. 3302.0.55.005, ABS, Canberra

Australian Bureau of Statistics, Population Projections, Australia, 2017 to 2066, cat. no. 3222.0, ABS, Canberra.

Australian Bureau of Statistics and the Australian Institute of Health and Welfare, The Health and Welfare of Australia's Aboriginal and Torres Strait Islander Peoples, cat. no. 4704.0, ABS, Canberra.

Australian Institute of Health and Welfare 2017, Trends in Indigenous mortality and life expectancy, 2001-2015: evidence from the Enhanced Mortality Database, Cat. no. IHW 174, Canberra, AIHW.