Avoidable mortality trends in Aboriginal and non-Aboriginal populations in the Northern Territory, 1985-2004
Shu Qin Li, Natalie Gray, Steven Guthridge, Sabine Pircher
Northern Territory Department of Health and Families
Zhiqiang Want
School of Medicine, University of Queensland
Yuejen Zhao
Northern Territory Department of Health and Familie
Submitted: April 2009 Revision requested: July 2009 Accepted: August 2009
Correspondence to:
Shu Qin Li, Health Gains Planning, NT Department of Health and Families, PO Box 40596,
Casuaring NT 0811. Fax: (08) 8985 8075; e-mail:
Key words: avoidable mortality, Aboriginal health, Northern Territory, health care
Objectives: To analyse rates of avoidable mortality in Aboriginal and non-Aboriginal residents of the Northern Territory (NT) from 1985 to 2004, in order to assess the contribution of health care to life expectancy improvements.
Methods: Australian Bureau of Statistics (ABS) death registration data for NT residents were used to identify ‘avoidable’ deaths, with further separation into three categories of conditions amenable to either medical care or health policy, and a category for ischaemic heart disease (IHD). A Poisson regression model was used to calculate the average annual change in avoidable mortality by sex and Aboriginality in the NT compared with Australia as a whole.
Results: In the 20 years between 1985 and 2004, avoidable mortality rates fell 18.9% in NT Aboriginal people, 61.1% in NT non-Aboriginal people and 59.5% in Australians overall. NT Aboriginal people continued to experience higher avoidable mortality than other Australians and the disparity increased over time. Most of the decline in avoidable mortality for Aboriginal Territorians occurred for conditions amenable to medical care.
Conclusion: Medical care has made a significant contribution to improvements in Aboriginal life expectancy in the NT; however, reductions in avoidable mortality from IHD and conditions amenable to health policy have been variable.
Implications: The results highlight the need for ongoing investment in comprehensive programs incorporating appropriate health policy interventions and management of chronic diseases.
Introduction
In the 17 years to 2000, life expectancy in Australia increased from 79 to 83 years for women and from 72 to 78 years for men.1 Although considerable attention has justifiably been given to the substantial gap in life expectancy between non-Aboriginal and Aboriginal Australians, a recent article demonstrated that for the Northern Territory (NT) there has been a significant improvement in Aboriginal life expectancy since the 1960s.2 Between 1967 and 2004, life expectancy at birth in the NT increased from 54 to 68 years for Aboriginal women, and from 52 to 60 years for Aboriginal men. For Aboriginal women, this represented a 5.6 years reduction in the gap between their life expectancy and that of all Australian women.
There is also evidence that despite an emerging epidemic of chronic disease in the NT Aboriginal population,3 the increase in Aboriginal mortality rates from ischaemic heart disease (IHD) and diabetes has slowed since 1990 and the mortality rate from chronic obstructive pulmonary disease (COPD) has fallen.4 While these figures give some cause for optimism, from a health service planning perspective it is useful to separate the contribution of the health care system, from the more general contribution of social determinants of health, to these outcomes.
The concept of ‘avoidable mortality’ builds on Rutstein’s pioneering work in 1976 on ‘amenable mortality’, and the extensive work on ‘preventable mortality’, which recognised that some conditions were responsive to interventions such as health care, lifestyle change and environmental modification. 5,6,7 Avoidable mortality provides a methodology to assess the extent to which declining mortality rates can be attributed to health care including medical interventions, public health programs and population-based health strategies. This approach labels as ‘avoidable’ deaths from conditions for which death could be avoided by timely and effective health care.8 It needs to be acknowledged that the sensitivity of this method may vary with the selection of causes of death, and that there is currently no ‘gold standard’ of causes that are used when analysing this population health indicator.7 Although debate about the list of conditions that constitute avoidable mortality has limited the capacity for international comparisons of the effectiveness of different approaches to health care,8,9,10 it remains a useful epidemiological tool to compare trends in avoidable and non-avoidable mortality.
A recent analysis of avoidable mortality in Australia reported that between 1968 and 2001 health care played a significant role in overall mortality reductions, with avoidable mortality rates falling 70% and non-avoidable mortality rates falling 34%.8 However, the benefits of health care have not been distributed equally throughout the population, with people of higher socio-economic status receiving disproportionate benefit leading to a widening of health inequalities.11 Overseas data suggest a similar disparity in avoidable mortality for certain ethnic groups, with Maori and Pacific Islands people in New Zealand experiencing avoidable mortality rates more than twice those of the total population10 and migrants in the Netherlands also experiencing higher mortality from conditions deemed to be avoidable.12 To date, there has been little information available on avoidable mortality rates for Aboriginal Australians.
Vigorous and collective efforts have been made over the past two decades to tackle excess mortality among the NT Aboriginal population, including the development of the NT Preventable Chronic Disease Strategy, which has prioritised the prevention and management of chronic diseases.13 This study aims to analyse avoidable mortality rates in Aboriginal and non-Aboriginal Territorians, examine trends over time, and measure the impact of health care on mortality reductions in the NT in order to assess the success of current programs and to inform continuing efforts to reduce Aboriginal mortality.
Methods
Data
This study uses Australian Bureau of Statistics (ABS) death registration data for both NT and Australia. For the NT Aboriginal population the coverage and identification of deaths are known to be close to 100% from 1988 when Indigenous status was first recorded on NT death registration forms.2,14 For the years 1967 to 1987, extensive data validation has been previously performed manually for each individual record, and where necessary, Indigenous status was derived from names, residence, place of birth and other information from death registrations forms.2,15 The near complete identification of Indigenous deaths in the NT mortality data since the 1960s provided reliable data for long-term trend analysis. NT population data were based on the Australian Bureau of Statistics 2001 Census.16
The ABS codes the underlying cause of death using the International Classification of Diseases and Related Health Problems, 9th revision (ICD-9-CM)17 for deaths registered from 1981 to 1996, and the 10th revision (ICD-10-AM)18 for deaths registered from 1997 onwards. To ensure comparability with other Australian avoidable mortality analyses,8 an age limit of 74 years was applied for this study.
Following Korda and Butler,8 avoidable deaths were classified into three categories (Appendix A): conditions amenable to medical care (such as asthma, pneumonia and breast cancer), conditions responsive to population-based health policies (smoking, alcohol consumption and motor vehicle accidents) but considered to lack effective treatment once the conditions have developed (such as lung cancer, chronic liver disease and cirrhosis, and motor vehicle accidents), and ischaemic heart disease (IHD), which is considered partly amenable to medical care but primarily responsive to health policy. Deaths from remaining conditions were classified as ‘non-avoidable’ by health care interventions.
Statistical analysis
Annual avoidable and non-avoidable mortality rates by year of death, sex and Indigenous status were calculated from 1985 to 2004, and age-adjusted using the 2001 Australian estimated resident population.
Poisson regression was used to estimate the average annual changes in avoidable mortality by sex and Aboriginality in the NT, compared with the overall Australian population. The Poisson regression model was further used to estimate the annual change in avoidable mortality by the three categories and major conditions of interest, such as diabetes and stroke. Various interaction terms were added to the Poisson regression model to test differences in annual changes between NT Aboriginal and all Australians, and between NT non-Aboriginal and all Australians.
Stata software (version 8; Stata Corp, College Station, Tex, USA) was used for all statistical analysis. Ethics approval was granted by the Human Research Ethics Committee of the NT Department of Health and Families and the Menzies School of Health Research.
Results
Overall trends in avoidable mortality
During the 20-year period from 1985 to 2004, 6411 NT residents died from conditions that were considered to be avoidable (Table 1). These comprised 40.5% of total NT deaths. Although Aboriginal people account for 28% of the NT population, they experienced 54% of total avoidable deaths.
Table 1. Number of avoidable deaths by Aboriginality, Northern Territory, five year period, 1985 to -2004
Time trends in avoidable and non-avoidable mortality for the NT and all Australians are shown in Figure 1. Avoidable mortality rates in the NT population were consistently higher, and fell more slowly, than those in all Australians during the study period. The avoidable mortality rates in NT residents fell from 371 to 195 deaths per 100 000 person years (47.6%) and the rates in all Australians fell from 269 to 109 deaths per 100 000 person years (59.6%). Using the Poisson regression model, the average annual reduction in avoidable mortality was 3.5% (95% CI: 3.11%-3.92%) in the NT and 4.6% (95% CI: 4.51%-4.60%) in all Australians. This difference in average annual reduction was statistically significantly (p<0.05). The average annual reduction for non-avoidable mortality was also significantly higher (2.6%, 95% CI: 2.16%-2.98%) for the NT residents than for all Australians (1.5%, 95% CI: 1.47%-1.56%).
Figure 1. Avoidable and non-avoidable mortality, NT and Australia, 1985 to 2004
Trends in total avoidable mortality by Aboriginality and sex
Avoidable mortality rates declined over time in all population groups (Table 2), however the rates in NT Aboriginal people started at nearly three times the comparable Australian rates, and the disparity increased over time. Avoidable mortality rates fell from 638 in 1985 to 517 deaths in 2004 per 100 000 person years (18.9%) in Aboriginal Territorians, from 290 in 1985 to 113 in 2004 deaths per 100 000 person years (61.1%) in non-Aboriginal Territorians, and from 269 in 1985 to 109 in 2004 deaths per 100 000 person years (59.5%) in all Australians.
Table 2. Age-adjusted avoidable mortality rate by sex and Aboriginality, NT and Australia, five year period, 1985 to 2004
The average annual reduction in avoidable mortality rates was 1.7% (95% CI: 1.10%-2.23%) in the total NT Aboriginal population with Aboriginal males experiencing a fall of 1.8% (95% CI: 1.03%-2.51%) and Aboriginal females a fall of 1.4% (95% CI: 0.56%-2.33%). This compares with an estimated average annual avoidable mortality reduction for the NT’s non-Aboriginal population of 4.7% (95% CI: 4.10%-5.25%). The overall Australian average annual reduction in avoidable mortality rate was 4.5% (95% CI: 4.47%-4.56%), comprising 4.8% (95% CI: 4.73%-4.84%) in males and 4.2% (95% CI: 4.11%-4.25%) in females. The differences in average annual reduction rate between NT Aboriginal population and other Australians were statistically significant (p<0.05).
Trends in three categories of avoidable mortality
Throughout the study period, mortality rates from conditions amenable to medical care were four to five times higher in Aboriginal Territorians than Australians as a whole. These rates declined substantially from 1985 to 2004 in all population groups (Table 3). The estimated average annual reduction in the avoidable mortality rate for these conditions for Aboriginal and non-Aboriginal Territorians was 3.2% (95% CI: 2.45%-3.99%) and 3.8% (95% CI: 2.76%-4.77%) respectively, compared with 3.6% (95% CI: 3.57%-3.70%) for all Australians. These differences were not statistically significant (p > 0.05). The decline in mortality rates for medical care conditions was observed for most common conditions, with the notable exception of some chronic diseases including diabetes, nephritis and nephrosis.
Table 3. Age-adjusted avoidable mortality rate from conditions amenable to medical care, by sex and Aboriginality, five year period, NT and Australia, 1985 to 2004
Mortality rates from avoidable conditions responsive to health policy were three to four times higher for Aboriginal Territorians than for Australians as a whole. This ratio persisted throughout the study period. Further, while mortality rates from these causes declined consistently over time in non-Aboriginal Territorians and in all Australians, andwith a narrowing of the gap between non-Aboriginal Territorians and all Australians existed, there was only marginal change in the NT’s Aboriginal population (Table 4). For Aboriginal males there was a minor improvement, while for Aboriginal females there was an initial increase in mortality rates, with no overall improvement for Aboriginal women across the entire 20 years.
Table 4. Age-adjusted avoidable mortality rate from conditions amenable to health policy, by sex and Aboriginality, five year period, NT and Australia, 1985-2004
Table 5 demonstrates a steady decline in Australian and NT non-Aboriginal mortality from IHD between 1985 and 2004. In contrast, IHD mortality in the NT Aboriginal population increased between 1985 and 1994, by 23.9% for males and 33.3% for females. This was followed by a marginal decline of 2.2% for Aboriginal males and 5.3% for Aboriginal females between 1995 and 2004. This has led to a substantial increase in the gap in mortality rates from IHD between Aboriginal Territorians and both non-Aboriginal Territorians and all Australians.
Table 5. Age-adjusted avoidable mortality rate from ischaemic heart disease by sex and Aboriginality, NT and Australia, five year period, 1985-2004
Discussion
The results of this analysis confirm that, while Aboriginal Territorians continue to experience significantly higher avoidable mortality than non-Aboriginal people, the health care system has made a considerable contribution to the fall in NT Aboriginal mortality rates between 1985 and 2004. This is demonstrated by both the substantial decline in deaths from conditions within the medical care category and by the more rapid fall in avoidable than non-avoidable causes of death.8 Nevertheless, the reduction in avoidable mortality rate for Aboriginal Territorians was less than one-third that of non-Aboriginal Territorians confirming that improved outcomes have not been shared equally.