TRENDS IN MORTALITY

Analyses of trends in Indigenous mortality must be undertaken with care, because of the limited understanding of the ways in which changes in the recording of Indigenous status on death registrations have affected the recorded numbers of deaths.

Various statistical measures may be used to assess trends in mortality over time. A measure derived from comprehensive life tables - such as life expectancy at birth - is generally to be preferred as it takes into account age-sex specific death rates (and any shifts in those rates) across all ages. However, the construction of such a measure depends on the availability of an accurate series of age-sex specific population estimates together with an accurate series of age-sex specific counts of deaths. Recent work by the ABS has improved the demographic estimates available to support trend analyses, but those estimates are still regarded as experimental. Any discussion of Indigenous mortality trends should therefore be based on a range of analytical measures to provide a broader understanding of possible trends than can be obtained from any one measure.

This section examines changes over time in all-cause mortality rates, infant mortality rates, age at death and cause-specific mortality rates. Each of these measures has advantages and limitations for understanding trends. These are discussed in the relevant sections of the chapter.

The mortality patterns observed among Australia's Indigenous people are slow moving, and therefore trends are best detected over long periods of time. There is some evidence of more rapid progress in reducing mortality among the Indigenous population in other countries (Ring & Brown 2003). However, the potential for analysis of long-term trends in Indigenous mortality in Australia is greatly constrained by the availability of consistently accurate data over time. When assessed in terms of consistency over time in the number of recorded deaths identified as Indigenous, Western Australia, South Australia and the Northern Territory are each judged to have had reasonably high and reasonably stable coverage of Indigenous deaths since around 1989, although the level of coverage is different in each of those jurisdictions. To test whether the observed trends would have differed if the analyses had been based on a different time window, several different time periods were tested. While the estimated rate of changes differed, there was no change in the direction of trends or their significance. As there is a consistent time series of population estimates from 1991, data for Western Australia, South Australia and the Northern Territory for the period 1991-2005 have been used for the analyses of Indigenous all-cause and infant mortality in this chapter. Due to changes in the coding of cause of death in 1997, the analyses of cause-specific mortality have been based on the period 1997-2005.

It is important to note, that in 2001, the Indigenous populations of Western Australia, South Australia and the Northern Territory together represented 32% of the total estimated Indigenous population in Australia (14% in Western Australia, 6% in South Australia and 12% in the Northern Territory). As a consequence, any statement about the possible detection of trends in mortality in these jurisdictions can give, at best, a partial account of trends in Indigenous mortality in Australia as a whole.

A further constraint in assessing time series trends in Indigenous mortality is the relatively small size of the Indigenous population which means that, even with the high mortality rates being experienced, the absolute numbers of deaths of Indigenous people recorded each year in each jurisdiction have, for statistical purposes, been quite small. Between 1991 and 2005, annual deaths for Western Australia, South Australia and the Northern Territory averaged 125, 373 and 415 respectively. Thus, the year to year fluctuations in the numbers of deaths can be quite large relative to any gradual underlying trend, and it is not meaningful to look at changes in mortality from one year to the next. Longer term changes have been analysed in several ways - examining the rate of change between the beginning and end year, and modelling trends throughout the period. A limitation of the first method is that the results are affected by the particular choice of the start and end year, whereas the trends modelling takes account of all the observations throughout the period. In this chapter, statements about the broad pace of change occurring over a number of years have been based on the fitted trends. When the trend has an estimated p-value of less than 0.05, it is characterised in subsequent text as 'significant'.

The mortality trends analyses presented in this chapter differ from analyses presented in the 2005 edition of this report. While the 2005 edition presented crude Indigenous mortality rates only, in this edition mortality rates for both Indigenous and other Australians are presented using age standardised data. While there is an ongoing debate as to whether standardisation is necessary or even appropriate for this type of analyses because trends may not be the same in all age groups, directly age standardised rates have been used to enable comparisons to be made between mortality trends for Indigenous and other Australians. Due to the inclusion of a 'not stated' category of Indigenous status in 1998 (before which 'not stated' responses were included with non-Indigenous deaths), Indigenous mortality rates have been compared with the mortality rates of 'Other' Australians (which include deaths of both non-Indigenous people and deaths for which Indigenous status was not stated).

While data about changes in mortality among Indigenous Australians are important in their own right, and can inform the design and evaluation of policy and interventions, it is also important to develop an understanding of how these changes in mortality compare with those for other Australians. Mortality rate ratios have therefore been added to this section since the 2005 edition to give an indication of whether the differences between mortality rates for Indigenous and other Australians are lessening over time. Any discussion of trends in Indigenous mortality should be read in the context of changes in mortality for other Australians over the same period.


All-cause mortality

The results presented in this section are for recorded deaths, and assume no change in the rate at which Indigenous status is reported on death registrations. The impact of such changes in recording on the robustness of the conclusions is provided in the later section 'The sensitivity of mortality trends to changes in Indigenous identification'.

Between 1991 and 2005, there was a significant decline in recorded mortality rates in Western Australia, for Indigenous Australians (table 9.33). Over this period there was an average yearly decline in recorded deaths of around 23 deaths per 100,000 population for Indigenous people - this is equivalent to a reduction in the death rate of around 20% during the period of analyses. Significant declines in mortality were observed for both Indigenous males and females in Western Australia. In the Northern Territory, there was a significant decline in recorded mortality rates for Indigenous females only. Over the period, there was an average yearly decline in recorded deaths of around 20 deaths per 100,000 population for Indigenous females - this is equivalent to a reduction in the death rate of around 15% between 1991 and 2005.

Over the same period, there were significant declines in recorded mortality rates for other Australians in Western Australia, South Australia and the Northern Territory. In Western Australia there was an average yearly decline in the rate of around 15 per 100,000 for other Australians (equivalent to a reduction in the death rate of around 26% during the period of analyses); in South Australia there was an average yearly decline in the rate of around 14 per 100,000 for other Australians (equivalent to a reduction in the death rate of around 25% during the period of analyses); and in the Northern Territory there was an average yearly decline in the rate of around 43 per 100,000 for other Australians (equivalent to a reduction in the death rate of around 49% during the period of analyses).

Despite declines in Indigenous mortality in recent years, the mortality rate ratio between Indigenous and other Australians for all causes of death increased significantly in South Australia and the Northern Territory over the period 1991 to 2005, while in Western Australia there was an increase in the rate ratio for males only.

9.33 AGE STANDARDISED DEATH RATES(a)(b), by Indigenous status - 1991-2005
		1991	1992	1993	1994	1995	1996	1997	1998	1999	2000	2001	2002	2003	2004	2005
Indigenous rate per 100,000
WA
	Males	1 799	1 568	1 789	1 672	1 785	1 731	1 522	1 702	1 522	1 697	1 639	1 274	1 422	1 651	1 512
	Females	1 523	1 299	1 466	1 517	1 394	1 197	1 095	1 109	1 043	1 183	861	1 155	899	1 389	1 293
	Persons	1 661	1 433	1 628	1 597	1 583	1 452	1 299	1 387	1 270	1 419	1 211	1 206	1 139	1 518	1 397
SA
	Males	1 420	1 054	1 157	1 597	1 473	1 363	2 006	1 675	1 077	1 511	1 399	1 060	1 522	1 168	1 392
	Females	1 077	956	1 058	1 055	984	967	848	1 013	1 095	1 233	1 041	893	780	1 218	841
	Persons	1 255	1 010	1 105	1 301	1 210	1 164	1 355	1 294	1 111	1 354	1 219	970	1 121	1 197	1 096
NT
	Males	2 075	2 484	1 955	2 138	2 154	1 756	2 630	2 021	1 978	2 068	2 127	2 065	2 105	1 896	1 874
	Females	1 831	1 634	1 499	1 604	1 473	1 166	1 818	1 490	1 601	1 688	1 341	1 449	1 311	1 477	1 321
	Persons	1 947	1 985	1 697	1 839	1 776	1 460	2 091	1 725	1 786	1 866	1 695	1 731	1 666	1 675	1 574
Other rate per 100,000(c)
WA
	Males	979	955	975	975	916	933	887	860	826	811	778	770	758	757	757
	Females	629	623	641	625	604	616	600	576	556	548	548	552	540	532	525
	Persons	783	769	789	779	743	757	729	704	678	667	653	651	640	634	631
SA
	Males	934	938	963	939	906	940	874	835	825	777	746	739	723	686	674
	Females	598	617	622	608	596	616	593	560	556	526	526	544	526	501	484
	Persons	746	758	773	753	734	760	719	684	678	639	627	635	617	587	573
NT
	Males	1 764	1 259	1 434	1 357	1 235	1 064	1 104	879	875	995	838	811	764	714	802
	Females	722	952	801	839	768	701	648	717	644	495	610	514	565	450	494
	Persons	1 231	1 117	1 104	1 100	1 002	893	879	814	774	762	738	676	673	596	666
Rate ratio(d)
WA
	Males	1.9	1.8	1.8	1.8	2.0	1.8	2.2	2.1	1.9	2.2	2.3	2.0	2.2	2.3	2.3
	Females	2.0	1.8	1.8	1.9	1.8	1.5	1.8	1.8	1.9	2.1	1.6	1.9	1.6	2.3	2.0
	Persons	2.2	2.0	2.0	2.1	2.1	1.9	2.2	2.1	2.1	2.4	2.1	2.1	2.1	2.5	2.4
SA
	Males	1.4	1.1	1.2	1.6	1.6	1.5	2.3	1.9	1.3	1.8	1.7	1.3	1.9	1.6	1.9
	Females	1.3	1.2	1.3	1.3	1.3	1.3	1.2	1.4	1.6	1.8	1.5	1.3	1.2	2.0	1.3
	Persons	1.6	1.3	1.4	1.6	1.6	1.6	1.9	1.8	1.6	2.0	1.8	1.5	1.7	1.9	1.8
NT
	Males	1.2	2.0	1.4	1.6	1.7	1.7	2.4	2.3	2.3	2.1	2.5	2.5	2.8	2.7	2.3
	Females	1.5	1.5	1.4	1.5	1.5	1.3	2.1	1.8	2.1	2.2	1.8	2.1	1.9	2.5	2.0
	Persons	1.6	1.8	1.5	1.7	1.8	1.6	2.4	2.1	2.3	2.4	2.3	2.6	2.5	2.8	2.4
(a) Deaths are based on year of registration of death.
(b) Rates have been directly age standardised using the 2001 Australian standard population.
(c) Other includes deaths of non-Indigenous people and those for whom Indigenous status was not stated.
(d) Mortality rate for Indigenous Australians divided by the mortality rate for other Australians.
Source: AIHW National Mortality Database

Infant mortality rates

Consistent with the all-cause mortality analyses, the results presented in this section are also for recorded deaths, and assume no change in the rate at which Indigenous status is reported on infant deaths registrations. Indigenous status on infant death registrations has generally been more comprehensively recorded than for deaths at older ages.

There was a significant decline in recorded mortality for Indigenous infants in Western Australia, South Australia and the Northern Territory during the period 1991-2005 (table 9.34). The average yearly decline in infant mortality was around 0.8 deaths per 1,000 live births in each of the three jurisdictions - equivalent to a reduction in the infant mortality rate of around 41% in Western Australia, 58% in South Australia and 46% in the Northern Territory.

Over the same period, there was a significant decline in recorded infant mortality for other Australian infants in Western Australia and South Australia - an average yearly decline of around 0.2 deaths per 1,000 live births in Western Australia (equivalent to a reduction in the infant mortality rate of around 39%) and an average yearly decline of around 0.1 deaths per 1,000 live births in South Australia (equivalent to a reduction in the infant mortality rate of around 26%).

The relative difference between Indigenous and other infant mortality rates significantly declined over the period 1991-2005. The rate ratio, which is the Indigenous rate divided by the rate for other Australians, declined significantly in South Australia and the Northern Territory by an average of 0.1 per year in South Australia (from around 4.0 in 1991 to 2.0 in 2005) and by an average of 0.04 per year in the Northern Territory (from around 1.9 in 1991 to 1.5 in 2005). The rate difference, which is the Indigenous rate minus the rate for other Australians, declined significantly in Western Australia, South Australia and the Northern Territory (from around 20 per 1,000 births to 8 per 1,000 births in Western Australia and from around 11 per 1,000 births to 5 per 1,000 births in the Northern Territory) and by an average of 0.8 per 1,000 per year in South Australia (from around 15 per 1,000 births to 5 per 1,000 births).

9.34 INFANT MORTALITY RATES(a)(b), by Indigenous status - 1991-2005
	1991	1992	1993	1994	1995	1996	1997	1998	1999	2000	2001	2002	2003	2004	2005
Indigenous
WA	(c)26.1	(c)24.1	16.3	19.6	18.1	24.1	13.6	17.0	16.7	16.9	16.3	16.2	15.4	11.1	11.9
SA	20.2	23.2	17.3	7.5	16.2	12.6	8.5	4.5	7.8	11.1	4.9	14.7	6.9	6.1	9.7
NT	24.7	28.1	29.4	18.7	18.5	19.4	29.4	22.6	19.0	22.9	16.0	15.6	12.9	17.9	16.2
Other(d)
WA	(c)6.0	(c)5.9	5.2	4.6	4.3	5.3	4.8	4.2	3.9	3.4	4.3	3.5	3.3	3.4	4.0
SA	5.1	5.5	4.9	4.7	5.5	4.7	4.6	4.0	4.2	4.4	4.6	4.7	3.6	3.0	4.9
NT	13.2	15.9	17.8	10.9	10.4	11.7	15.9	12.3	12.5	16.2	12.7	11.0	9.7	13.2	11.0
Rate ratio(e)
WA	(c)4.4	(c)4.1	3.1	4.2	4.2	4.5	2.8	4.0	4.3	4.9	3.8	4.6	4.7	3.3	2.9
SA	4.0	4.2	3.6	1.6	3.0	2.7	1.8	1.1	1.9	2.5	1.1	3.1	1.9	2.0	2.0
NT	1.9	1.8	1.7	1.7	1.8	1.7	1.8	1.8	1.5	1.4	1.3	1.4	1.3	1.4	1.5
Rate difference(f)
WA	(c)20.1	(c)18.2	11.1	15.0	13.8	18.8	8.8	12.8	12.8	13.4	12.0	12.7	12.1	7.7	7.9
SA	15.1	17.6	12.5	2.9	10.8	7.9	3.8	0.6	3.6	6.7	0.3	10.0	3.3	3.1	4.8
NT	11.4	12.2	11.6	7.8	8.1	7.6	13.5	10.3	6.5	6.6	3.3	4.6	3.2	4.7	5.1
(a) Infant deaths per 1,000 live births.
(b) Deaths are based on year of registration of death and state of usual residence. Births are based on year of registration.
(c) The average of births over 1993-1995 in Western Australia was used to as the denominator for the estimates of the infant mortality rates for 1991 and 1992 to correct for errors in births recorded for 1991 and 1992.
(d) Other includes deaths of non-Indigenous people and those for whom Indigenous status was not stated.
(e) Mortality rate for Indigenous Australians divided by the mortality rate for other Australians.
(f) Mortality rate for Indigenous Australians minus the mortality rate for other Australians.
Source: AIHW National Mortality Database

Cause-specific mortality

Another potentially informative approach to assessing mortality trends is to examine changes in the pattern of deaths, by specific causes of death. These analyses have the advantage that they may reveal trends that are disguised by the more heterogeneous aggregate of mortality figures. But the available data constrain the analyses that can be done, and caution must be exercised when interpreting changes. First, the numbers of deaths that underlie the analysis diminish when the data are disaggregated to specific causes and the finer the disaggregation, the smaller the numbers and the larger the fluctuations relative to any underlying trend. The analyses undertaken for this report have been confined to five main causes of death - diseases of the circulatory system; diseases of the respiratory system; external causes; endocrine, nutritional and metabolic diseases; and neoplasms. Second, there was a change in the classification and coding of causes of death between 1996 and 1997. ICD-9 was used to classify causes of death prior to 1997 and ICD-10 has been used to classify causes of death from 1997 onwards. As these changes affect the comparability of the data for the two periods, the analyses reported here are for the period 1997-2005. Third, when analysing five causes of death for three jurisdictions and for three population groups (persons, males and females), some statistically significant changes may arise by chance - attention should therefore be paid to those causes that show some consistency of pattern, not to individual differences or changes.

Consistent with the analyses of all-cause mortality, the results presented in this section are for recorded deaths and assume no change in the rate at which Indigenous status is reported on deaths registrations, including no changes in rates of recording Indigenous status by specific causes of death. The impact of such changes in recording on the robustness of the conclusions is provided in the latter section 'The sensitivity of mortality trends to changes in Indigenous identification'.

Of the five causes examined, only diseases of the circulatory system showed consistently significant changes in recorded mortality (table 9.35).

9.35 CAUSE-SPECIFIC AGE STANDARDISED MORTALITY RATES(a)(b)(c), by Indigenous status - 1997-2005
	1997	1998	1999	2000	2001	2002	2003	2004	2005
	rate	rate	rate	rate	rate	rate	rate	rate	rate
Circulatory diseases (I00-I99)
Indigenous rate(b)	606.0	539.4	510.4	505.0	415.6	396.3	406.9	502.4	435.5
Other rate(b)(d)	297.6	285.0	267.3	251.6	245.2	235.9	228.6	220.5	217.8
Rate ratio(e)	2.0	1.9	1.9	2.0	1.7	1.7	1.8	2.3	2.0
Respiratory diseases (J00-J99)
Indigenous rate(b)	152.9	193.2	143.5	164.2	164.8	162.1	142.7	199.2	144.2
Other rate(b)(d)	63.3	57.6	54.2	60.1	57.5	62.9	62.0	57.6	52.8
Rate ratio(e)	2.4	3.4	2.6	2.7	2.9	2.6	2.3	3.5	2.7
External causes (V01-Y98)
Indigenous rate(b)	110.8	139.1	105.3	130.6	127.1	124.4	123.8	121.1	157.8
Other rate(b)(d)	41.8	47.7	41.8	43.8	41.1	38.8	39.9	38.9	41.0
Rate ratio(e)	2.6	2.9	2.5	3.0	3.1	3.2	3.1	3.1	3.9
Endocrine, Nutritional and metabolic diseases (E00-E89)
Indigenous rate(b)	158.1	112.6	137.1	171.0	174.7	151.4	128.0	160.9	166.6
Other rate(b)(d)	23.1	21.1	21.6	21.4	22.2	22.2	22.0	24.8	24.0
Rate ratio(e)	6.8	5.3	6.3	8.0	7.9	6.8	5.8	6.5	6.9
Neoplasms (C00-D48)
Indigenous rate(b)	245.9	224.4	196.9	263.4	214.9	233.2	247.3	260.2	243.0
Other rate(b)(d)	203.2	194.4	195.3	192.4	190.4	191.0	187.1	189.8	188.7
Rate ratio(e)	1.2	1.2	1.0	1.4	1.1	1.2	1.3	1.4	1.3
(a) Deaths are based on year of registration of death and state of usual residence.
(b) Directly age standardised rate per 100,000 population using the 2001 estimated resident population.
(c) Data for WA, SA and NT combined
(d) Comprises deaths of non-Indigenous persons and those for whom Indigenous status was not stated.
(e) Mortality rate for Indigenous persons divided by the mortality rate for other persons.
Source: AIHW National Mortality Database

Over the period 1997-2005, there were significant declines in recorded mortality from circulatory diseases for Indigenous people in Western Australia, South Australia and the Northern Territory (the mortality in 2005 was around three-quarters the rate in 1997). This was mainly due to a significant decline for males (a reduction in the mortality rate of around 32% during the period of analysis).

Over the same period, there were also significant declines in recorded mortality from circulatory diseases for other Australians (the mortality rate in 2005 being around three-quarters of the 1997 rate).

For external causes and neoplasms, there were significant declines in recorded mortality for other Australians over the period 1997-2005 however there were corresponding significant changes in the mortality rates for Indigenous Australians for these causes of death.

There was a significant increase in the rate ratio between Indigenous and other Australian mortality rates for external causes of death (from around 3 in 1997 to 4 in 2005).


The sensitivity of mortality trends to changes in Indigenous identification

When analysing trends in recorded Indigenous mortality, it is important to try to distinguish changes that arise because of real changes in mortality from those that arise because of changes in the reporting of Indigenous status on deaths registrations. But only broad, indicative estimates of changes in coverage are available, so it is not possible to definitively dissect observed changes in recorded mortality into the real and reporting effects.

In the absence of such a definitive dissection, the fitted trends discussed earlier in this chapter have been examined for their sensitivity to changes in Indigenous coverage. If those trends were to persist under a range of plausible assumptions regarding coverage, that would add to the confidence that the trends reflect some real alteration in mortality and are not just artefacts of changes in coverage.

The same approach as was used in the 2005 edition of this report has been used here. Three scenarios for coverage were posed - constant coverage, increasing coverage and decreasing coverage.

• Under the constant coverage scenario, the numbers of deaths for the entire period under study were adjusted using coverage estimates derived from the most recent ABS analyses (relating to the period 2001-2005). These estimates are: Western Australia - 70%; South Australia - 64% and the Northern Territory - 92%.
• Under the increasing coverage scenario, deaths were adjusted by linearly increasing the coverage through the period under study - from 63% in 1991 to 70% in 2005 for Western Australia; from 58% to 64% for South Australia; and from 87% to 92% for the Northern Territory.
• Under the decreasing coverage scenario, deaths were adjusted by linearly decreasing the coverage - from 77% in 1991 to 70% in 2005 for Western Australia; from 70% to 64% for South Australia; and from 97% to 92% for the Northern Territory.

The adjustments in the latter two scenarios were based on judgments about the largest plausible shifts in coverage during the decade. Of course, if any actual shift in coverage were more extreme than has been posed under these scenarios, then the observed trends in mortality might not persist. For all three scenarios, the population figures (used as denominators in the calculation of mortality rates) were re-estimated to reflect the altered number of deaths implied by each scenario.

• The declines in infant mortality rates for Indigenous Australians in Western Australia, South Australia and the Northern Territory during the period 1991-2005 remained statistically significant under all three identification coverage scenarios.
• The declines in mortality rates from diseases of the circulatory system during the period 1997-2005 remained significant under all three identification scenarios for Indigenous males and remained significant under the increasing identification scenario (which is the most likely scenario) for Indigenous people.

Other research and analyses

Chronic diseases

Another recent study also undertaken in the Northern Territory looked at long-term mortality trends in Indigenous deaths from chronic diseases (Thomas et al 2006). Trends in rates of mortality from six chronic diseases were analysed over the period 1977-2001 comparing Indigenous Australians in the Northern Territory with the total Australian population. The chronic diseases analysed were ischaemic heart disease (IHD), chronic obstructive pulmonary disease (COPD), cerebrovascular disease, diabetes mellitus, renal failure and rheumatic heart disease (RHD). Results found that over the 25 years examined, Northern Territory Indigenous mortality rates increased significantly for IHD and diabetes mellitus, however the rate of increase slowed significantly after 1990. For COPD, mortality increased before 1990, however significantly decreased thereafter. For RHD, the Indigenous mortality rate decreased for those aged less than 50 years and increased for those aged 50 years and over. The ratio of Indigenous mortality rates in the Northern Territory to total Australian mortality rates increased for all six chronic diseases. This increase was statistically significant for all diseases except COPD.

Life expectancy in the Northern Territory

A recent study was undertaken in 2007 by Wilson, Condon and Barnes to assess the extent of changes in life expectancy at birth for Indigenous Australians living in the Northern Territory over the period 1967-2004. Life expectancy at birth figures were calculated via life table calculations using Indigenous mortality data and population data from the Northern Territory.

The study found that the life expectancy at birth of Indigenous Australians has risen considerably in the Northern Territory, 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 gap between Indigenous and total Australian female life expectancy in the Northern Territory has narrowed between 1967 and 2004, while the gap between Indigenous and total Australian male life expectancy has remained the same.

Wilson, Condon and Barnes reported that declines in infant mortality accounted for a large amount of the increases in life expectancy for the Northern Territory Indigenous population between the late 1960s and mid 1980s, especially for males. A significant proportion of female life expectancy gains in this early period also came from other childhood and adult ages. From the mid 1980s to the early 2000s, declines in mortality at ages 45 years and over were responsible for the majority of life expectancy gains for both Indigenous males and females in the Northern Territory. For the total Australian population, improvements in middle age and older adult mortality were responsible for the vast majority of gains to Australian life expectancy over the entire period 1967 to 2004.

The gains in life expectancy for Indigenous males and females in the Northern Territory reported by Wilson, Condon and Barnes indicate that Indigenous health status has improved considerably in recent decades in the Northern Territory. There is still however substantial disparity between life expectancy measures of the Indigenous and non-Indigenous populations.

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