3238.0 - Estimates and Projections, Aboriginal and Torres Strait Islander Australians, 2001 to 2026 Quality Declaration 
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Contents >> Assumptions >> Mortality assumptions

MORTALITY ASSUMPTIONS

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

  • life expectancy at birth for each projection year is assumed; and
  • life tables, based on the 2010-2012 age/sex structure of mortality, are generated to match the assumed life expectancies at birth.

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

Assumptions for mortality at lower geographical levels are based on 2010-2012 differentials between Australia and each state or territory, groups of Indigenous Regions, and Remoteness Areas.

The effect of alternative life expectancy at birth assumptions on the number of projected deaths and size of the future Aboriginal and Torres Strait Islander population is described in Chapter 4.


Current life expectancy at birth

At the national level, Aboriginal and Torres Strait Islander life expectancy at birth for the period 2010-2012 is estimated to be 69.1 years for males and 73.7 years for females (see Life Tables for Aboriginal and Torres Strait Islander Australians, 2010-2012, cat. no. 3302.0.55.003).

As survivorship ratios are required on a financial year basis, life expectancy at birth estimates were adjusted to account for the six-month period between the midpoint of 2010-2012 (calendar year life expectancy) and 2010-11 (financial year life expectancy), resulting in life expectancy at birth of 69.0 years for Aboriginal and Torres Strait Islander males and 73.6 years for Aboriginal and Torres Strait Islander females for Australia for the year ending 30 June 2011, which form the starting point of the life expectancy at birth assumptions.


Trends in life expectancy at birth

The ABS has compiled life tables for Aboriginal and Torres Strait Islander Australians following the 1996, 2001, 2006 and 2011 Censuses of Population and Housing. Due to changes in methods, the 2006 and 2011 estimates of life expectancy at birth are not comparable to estimates for earlier periods. Assumptions about future levels of Aboriginal and Torres Strait Islander life expectancy at birth can therefore only be based on observed trends over the most recent intercensal period.

A recent study (Wilson, Condon and Barnes, 2007) found evidence that life expectancy at birth of Aboriginal and Torres Strait Islander people living in the Northern Territory has improved, increasing from 52 years for males and 54 years for females in the late 1960s to around 60 years for males and 68 years for females in recent years. The study found that improvements in infant mortality contributed considerably to increases in life expectancy at birth, particularly between the late 1960s and mid-1980s. Since then, life expectancy gains have been largely the result of improving mortality of Aboriginal and Torres Strait Islander people aged 45 years and over.

In addition, alternative measures indicate some improvement in mortality of Aboriginal and Torres Strait Islander Australians over time. For example, declines in Aboriginal and Torres Strait Islander mortality, as measured by age-standardised death rates, have been recorded for both males and females in Western Australia, and females in the Northern Territory between 1991 and 2005. Declines in Aboriginal and Torres Strait Islander infant mortality have also been recorded in Western Australia, South Australia and the Northern Territory over the period (see The Health and Welfare of Australia's Aboriginal and Torres Strait Islander Peoples, Oct 2010, cat. no. 4704.0, Wang Z and Li SQ, 2010, Mortality in the Northern Territory 1967-2006, Health Gains Planning Information Sheet, Dec 2010, Northern Territory Government, Casuarina NT and SCRGSP (Steering Committee for the Review of Government Service Provision) 2011, Overcoming Indigenous Disadvantage: Key Indicators 2011, Productivity Commission, Canberra).


Assumed life expectancy at birth

Three life expectancy at birth assumptions have been used to produce the three main series.
  • The first assumption is that Aboriginal and Torres Strait Islander life expectancy at birth will increase at the rate of 0.2 years per year for males and 0.15 years per year for females. This is close to the improvement currently being observed in the total Australia population. Based on this assumption, life expectancy would increase to 72.0 years for males and 75.9 years for females over the projection period.
  • The second mortality assumption is that Aboriginal and Torres Strait Islander life expectancy at birth will increase by 0.3 years per year for males and 0.25 years per year for females from 2010-11 levels. This level of improvement assumes that Aboriginal and Torres Strait Islander life expectancy at birth will increase at a faster rate than total Australian life expectancy (as assumed in the medium mortality assumption, Population Projections, Australia, 2012(base) to 2101, cat. no. 3222.0), resulting in a narrowing of the difference between Aboriginal and Torres Strait Islander and total Australian life expectancy at birth throughout the projection period. Based on this assumption, male life expectancy at birth would increase by 4.5 years and female life expectancy would increase by 3.75 years over the 15-year projection period, reaching 73.5 and 77.4 years respectively in 2026.
  • The third mortality assumption is that Aboriginal and Torres Strait Islander life expectancy at birth will increase at the rate of 0.5 years per year for males and 0.45 years per year for females from 2010-11 levels. Based on this assumption, male life expectancy at birth would increase by 7.5 years and female life expectancy would increase by 6.75 years over the 15 year projection period, reaching 76.5 and 80.4 years respectively in 2026.


State/territory variations in mortality

Aboriginal and Torres Strait Islander life expectancy at the national level has been calculated using an age-specific adjustment to allow for different patterns in mortality amongst different age groups. This adjustment could not be applied at the state and territory level. For this reason the Australia-level estimates are not strictly comparable with the state/territory level estimates. However, for the purpose of compiling estimates and projections, mortality differentials are calculated based on the relationship of 2010-2012 life expectancies at birth for each state/territory (without age adjustment) compared with Australia (with age adjustment).

Aboriginal and Torres Strait Islander life expectancy at birth differs between the states and territories. For the purposes of these projections, mortality differentials between each state/territory and Australia are calculated and applied to the assumed Australian life expectancies at birth (table 2.14) to obtain assumed life expectancy at birth for the states and territories. This method assumes that the mortality differentials, based on those observed during 2010-2012, will remain constant throughout the projection period.

Aboriginal and Torres Strait Islander life expectancy at birth for 2010-2012 is available for New South Wales, Queensland, Western Australia and the Northern Territory. Due to small numbers of deaths registered as Aboriginal and Torres Strait Islander it was not possible to produce Aboriginal and Torres Strait Islander life tables for the remaining jurisdictions. For the purposes of the projections, life expectancy at birth for Victoria and Tasmania is assumed to be the same as that for New South Wales, while life expectancy at birth for South Australia is assumed to be the same as that for Western Australia. Life expectancy at birth for the Australian Capital Territory is assumed to be the same as that derived for Sydney Indigenous Region.

2.14 ABORIGINAL AND TORRES STRAIT ISLANDER LIFE EXPECTANCY AT BIRTH AND MORTALITY DIFFERENTIALS(a), States and territories - 2010-2012

LIFE EXPECTANCY AT BIRTH
MORTALITY DIFFERENTIALS
Males
Females
Males
Females
years
years
%
%

New South Wales
70.5
74.6
102
101
Queensland
68.7
74.4
99
101
Western Australia
65.0
70.2
94
95
Northern Territory
63.4
68.7
92
93
Australia(b)
69.1
73.7
100
100

(a) Mortality differentials are calculated based on the relationship of 2010-2012 life expectancies at birth for each state/territory (without age adjustment), compared with Australia (with age adjustment).
(b) Includes Other Territories.



Regional variations in mortality

Indigenous Regions

To apply assumptions on life expectancy at birth for alternative geographies, Indigenous Regions (IREGs) were aggregated into two groups for each state and territory (except Tasmania and the Australian Capital Territory):
  • capital city IREG (for example, Adelaide IREG); and,
  • rest of state/territory IREGs combined (for example, Port Augusta IREG and Port Lincoln - Ceduna IREG combined).

To account for under-identification of deaths of Aboriginal and Torres Strait Islander people at the smaller geographic level, the number of registered deaths of Aboriginal and Torres Strait Islander people for each IREG group in 2010-2012 was adjusted using state and territory adjustment factors from the 2011 Census Data Enhancement (CDE) Indigenous Mortality Study. For more information about the derivation and use of adjustment factors in the compilation of Aboriginal and Torres Strait Islander life tables for the states and territories, see Life Tables for Aboriginal and Torres Strait Islander Australians, 2010-2012 (cat. no. 3302.0.55.003).

A life table methodology was used to obtain life expectancy at birth for 2010-2012 for each IREG group using adjusted deaths in conjunction with 2011 Aboriginal and Torres Strait Islander populations for each IREG group. Differentials were calculated as the ratio of Aboriginal and Torres Strait Islander life expectancy at birth for each IREG group and Australia with age adjustment (table 2.15). This method assumes that under-identification of Aboriginal and Torres Strait Islander deaths is consistent across all regions within each state and territory as information on under-identification is not available at the IREG level. Mortality differentials are assumed to remain constant throughout the projection period.

2.15 ABORIGINAL AND TORRES STRAIT ISLANDER LIFE EXPECTANCY AT BIRTH AND MORTALITY DIFFERENTIALS(a), Indigenous Regions - 2010-2012

MALE MORTALITY DIFFERENTIALS
FEMALE MORTALITY DIFFERENTIALS
Capital city IREG
Rest of state IREG group
Capital city IREG
Rest of state IREG group
%
%
%
%

New South Wales
106
100
105
99
Queensland
103
98
103
101
Western Australia
97
93
100
94
Northern Territory
94
91
95
92
Australia(b)
100
100
100
100

(a) Mortality differentials based on the relationship of 2010-2012 life expectancies at birth for each capital city IREG and rest of state IREG group, compared with Australian life expectancy (with age adjustment) of 69.1 years for males and 73.7 years for females.
(b) Includes Other Territories.


As noted above, Aboriginal and Torres Strait Islander life tables were not produced for Victoria, South Australia, Tasmania and the Australian Capital Territory. The following differentials have been used for IREG groups in these states and territories where sufficient data is not available to calculate a relevant differential:
  • for Victoria, Melbourne IREG uses the Sydney IREG differential, and rest of Victoria IREG uses the rest of New South Wales IREG group differential;
  • for South Australia, Adelaide IREG uses the Perth IREG differential, and the rest of South Australia IREG group uses the rest of Western Australia IREG group differential;
  • for Tasmania, the New South Wales state differential is used; and
  • for the Australian Capital Territory, the Sydney IREG differential is used.

Remoteness Areas

Aboriginal and Torres Strait Islander life expectancy at birth differentials for Remoteness Areas were calculated using the same method as that used for IREG groups (table 2.16). To account for the under-identification in deaths of Aboriginal and Torres Strait Islander people, the number of registered deaths of Aboriginal and Torres Strait Islander people in 2010-2012 for each Remoteness Area was adjusted using Australia-level adjustment factors from the CDE Indigenous Mortality Study. As with IREGs this method assumes that under-identification of Aboriginal and Torres Strait Islander deaths across Remoteness Areas is consistent across Australia. Mortality differentials are assumed to remain constant throughout the projection period.

Investigation into using adjustment factors for three categories of Remoteness Areas (Major Cities, Inner and Outer Regional combined and Remote and Very Remote combined) was undertaken, but insufficient data was available to accurately calculate reliable factors at this level.

2.16 MORTALITY DIFFERENTIALS(a), Remoteness Areas - 2010-2012

Males
Females
%
%

Major Cities
105
104
Inner and Outer Regional
103
102
Remote and Very Remote
90
92
Australia(b)
100
100

(a) Mortality differentials based on the relationship of 2010-2012 life expectancies at birth for each Remoteness Area, compared with Australian life expectancy (with age adjustment) of 69.1 years for males and 73.7 years for females.
(b) Includes Other Territories.




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