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3302.0.55.003 - Experimental Life Tables for Aboriginal and Torres Strait Islander Australians, 2005–2007  
Previous ISSUE Released at 11:30 AM (CANBERRA TIME) 25/05/2009   
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EXPLANATORY NOTES


INTRODUCTION

1 This publication contains abridged experimental life tables for male and female Aboriginal and Torres Strait Islander (Indigenous) Australians for the reference period 2005-2007.


Use of experimental Indigenous life tables

2 The life tables in this publication have been produced to enable the construction of ABS estimates and projections of the Aboriginal and Torres Strait Islander population of Australia for the period 1991 to 2021. 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.

3 Estimates of life expectancy at birth for Indigenous Australians are commonly used as a measure for assessing Indigenous population health and disadvantage. Due to significant changes in methodology, ABS strongly advises that comparisons between the estimates presented here and previously published estimates should not be made. Differences should not be interpreted as measuring changes in Indigenous life expectancy over time.


SCOPE

4 Life tables in this publication 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 Indigenous deaths in Victoria, South Australia, Tasmania and the Australian Capital Territory, it is not possible to construct life tables for these jurisdictions (see paragraphs 10-12 and 24-26).


CLASSIFICATIONS

Indigenous status

5 The term Indigenous is used in this publication to refer to Australian Aboriginal and Torres Strait Islander peoples. ABS Indigenous population statistics are based on responses to the ABS standard question for Indigenous identification (Question 7 of the 2006 Census), as below:

Diagram: Indigenous status


Australian Standard Geographical Classification

6 The Australian Standard Geographical Classification (ASGC) is a hierarchical classification system consisting of six interrelated classification structures. The ASGC provides a common framework of statistical geography and thereby enables the production of statistics which are comparable and can be spatially integrated.

7 For further information refer to Australian Standard Geographical Classification (ASGC) (cat. no. 1216.0).


METHOD FOR PRODUCING LIFE TABLES

8 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.

9 A life table may be complete or abridged, depending on the age intervals used in their compilation. Life tables in this publication 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 5-year age groups were considered more reliable than those for single years of age due to the small annual numbers of Indigenous deaths in the states and territories.

10 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.

11 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:
  • ASDRa,s = Deathsa,s / Populationa,s where
      • ASDRa,s is the age-specific death rate for age group a and sex s;
      • Deathsa,s is the number of deaths for age group a and sex s over a specified period of time; and
      • Populationa,s is the population of the age group a and sex s at the mid-point of the specified period.

12 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 publication 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.

13 The life tables in this publication are period life tables, based on mortality rates for 2005-2007. Period 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 Indigenous population

14 To produce life tables for the Indigenous population of Australia, information on the number of Indigenous deaths and the Indigenous population are required. Data quality issues are discussed in Chapter 2: Quality issues with Indigenous deaths and population data.

15 The life tables in this publication are based on the number of Indigenous deaths registered in 2005-2007 and Indigenous population estimates for 30 June 2006 from Experimental Estimates of Aboriginal and Torres Strait Islander Australians, Jun 2006 (cat. no. 3238.0.55.001).

16 To account for under-identification of Indigenous deaths in death registrations, the numbers of Indigenous deaths were adjusted according to the adjustment factors derived from the Census Data Enhancement Indigenous Mortality Quality Study (see table 3.5). This is described in Chapter 3: Data linkage to derive Indigenous deaths identification rates.

17 The adjusted numbers of Indigenous deaths were divided by three to obtain the average annual number of Indigenous deaths over the period 2005-2007, and in conjunction with 30 June 2006 Indigenous population estimates were used to calculate age-specific death rates for the Indigenous population. Life tables were then derived as described in paragraphs 11 and 12 above.


Life tables for the non-Indigenous population

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

19 Numbers of non-Indigenous deaths were obtained by subtracting the adjusted numbers of Indigenous deaths from the total number of deaths registered in 2005-2007 and dividing by three to obtain the average annual number of non-Indigenous deaths.

20 Estimates of the non-Indigenous population for 30 June 2006 from Experimental Estimates of Aboriginal and Torres Strait Islander Australians, Jun 2006 (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.


Graduation of life tables

21 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.

22 Life tables were first produced for the Indigenous and non-Indigenous populations as described above. While numbers of deaths were averaged for 2005-2007, 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 Indigenous and non-Indigenous life tables, for all states and territories and both sexes.

23 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 occured.


Victoria, South Australia, Tasmania and Australian Capital Territory

24 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.

25 Due to the small Indigenous populations of Victoria, South Australia, Tasmania and the Australian Capital Territory, these jurisdictions record very small numbers of Indigenous deaths annually (around 90, 135, 25 and 10 Indigenous deaths per year on average for 2005-2007 respectively).

26 For abridged life tables with an upper age group of 85 years and over, there are 19 age groups in total. Disaggregating the numbers of Indigenous deaths in these jurisdictions by age and 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 life tables for the Indigenous populations of these jurisdictions.


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

27 Estimates of life expectancy at birth for the total population presented in this publication differ from estimates published in Deaths, Australia, 2006 (cat. no. 3302.0). Estimates presented in this publication are derived from abridged life tables with an upper age limit of 85 years and over, using numbers of deaths registered in 2005-2007 and the population as at 30 June 2006, while life expectancy estimates in Deaths, Australia, 2006 (cat. no. 3302.0) are based on complete life tables with an upper age group of 115 years and over, using deaths according to month of occurrence in 2005-2007 and quarterly population estimates. In addition, graduation processes applied to both sets of life tables differ.


CONFIDENTIALITY

28 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.

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


ROUNDING

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


ACKNOWLEDGEMENTS

31 The ABS publications draw extensively on information provided freely by individuals, business, governments and other organisations. Their continued cooperation is very much appreciated; without it, the wide range of statistics published by the ABS would not be available. Information received by the ABS is treated in strict confidence as required by the Census and Statistics Act 1905.


RELATED PRODUCTS

32 Other ABS products which may be of interest to users include:

ADDITIONAL STATISTICS AVAILABLE

33 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 Experimental Life Tables for Aboriginal and Torres Strait Islander Australians, 2005-2007 (cat. no. 3302.0.55.003):
  • Table 1: Experimental Life Tables for Aboriginal and Torres Strait Islander Australians, State/Territory and Australia - 2005-2007
  • Table 2: Summary of Linked Deaths by Indigenous Status, State/Territory and Australia - 2006-2007

34 Additional demographic information is available on the ABS website <http://www.abs.gov.au>; click Themes, then under People click on Demography. Users can also access the full range of electronic ABS data from the ABS website.

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

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


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