Investigating Australia's burden of disease

Australia has a long history of vital registration, with excellent statistics on causes of death. These have been widely used to describe and monitor major public health issues, ranging from the progression (and decline) of chronic disease epidemics¹ to the emergence of recent threats to health such as HIV/AIDS.² Mortality data have been used to demonstrate the success of public health interventions, a good example of which is their use to document Australia's extraordinary success in reducing road traffic deaths since the early 1970s.³

The use of mortality data as a fundamental component of the public policy process is related in part to their widespread availability and timeliness. While statistics on causes of death are undoubtedly useful for public health surveillance, they do not adequately represent a population's level of health, as they disregard the importance of widely prevalent, severely disabling conditions. An ideal health metric is therefore one which simultaneously measures and contrasts both fatal and non-fatal health outcomes. Indeed, such a measure is needed to assess the benefits of health interventions, which may reduce both mortality and the period of life lived in a disabled state.

	Tobacco use alone accounts for about 10% of the entire national burden of disease...

It was precisely these considerations which motivated the development of disability-adjusted life years (DALYs) and disability-adjusted life expectancy (DALE) as the principal summary measures of population health in the Global Burden of Disease Study.⁴ DALYs are a gap measure; they measure the gap between a population's actual health and some defined health goal, while DALE belongs to the family of health expectancies, summarising the expected number of years to be lived in the equivalent of "full health". Both DALE and DALYs require a number of social value choices relating, among other things, to the valuation of time spent in less than perfect health, the definition of an implied norm for population health, and the differential weighting of years of life lived at different ages. Murray and Lopez have described in some detail how these social value choices were made in the Global Burden of Disease Study,⁵ arguing for the use of age weighting, discounting, and deliberative procedures which emphasise societal perspectives on health-state valuation, rather than individual preferences.

After the publication of the Global Burden of Disease Study, much work has been done in several countries to improve upon the methods and databases which were used to estimate disease burden in 1990. In this issue of the Journal, the results of the Australian Burden of Disease Study are reported by Mathers et al, summarising the health of Australians in 1996.⁶ The complete, extensive report and summary document were published by the Australian Institute of Health and Welfare in November 1999.^7,8

With this ground-breaking analysis, debates about public health priorities in Australia will be markedly better informed. Not only do policymakers now have a comprehensive and comparative view of the disease burden from 176 diseases and injuries, but, using DALYs as a common metric, the contribution of major risk factors to that burden has been quantified. The results, if perhaps not surprising, confirm the need to incorporate non-fatal health outcomes into health policy debates. For females, depression and dementia, neither of which are leading causes of death, are leading causes of disease burden, ranked 3rd and 4th, respectively, after ischaemic heart disease and stroke. Osteoarthritis and asthma are also among the top 10 causes of disease burden. Among males, the leading causes of disease burden (ischaemic heart disease, stroke, lung cancer, chronic obstructive pulmonary disease, suicide and road traffic accidents) are also leading causes of death. The importance of sequelae among non-fatal incident cases (eg, after stroke or chronic obstructive pulmonary disease) and the younger-age pattern of deaths in males (eg, from suicide or road traffic accidents) clearly increase the contribution of these causes to DALYs. This is precisely what one would hope a health metric would accomplish.

Much effort has been devoted to health promotion in Australia in recent decades, with considerable success, but the results of this study suggest that much more remains to be done. Tobacco use alone accounts for about 10% of the entire national burden of disease and injury in Australia, and, although much of this is attributable to past smoking, significant progress in further reducing the disease burden from tobacco must remain a public health priority. Interestingly, of the other attributable risk factors, both physical inactivity and obesity were found to contribute importantly (4%-6%) to disease burden, suggesting that the public health implications of the worldwide trend towards a higher prevalence of overweight adults may well have been seriously underestimated.⁹ Contrasting the leading causes of disease and injury burden with the contributions of the various risk factors provides a clear and objective statement about health priorities in Australia.

Are burden of disease studies useful? Do they justify the extra time and resources needed over and above a review of cause of death statistics, and, where available, health survey data on the incidence and prevalence of diseases, injuries and disabilities? Surely they do. The value of comparative assessments of the causes of health loss, be they fatal outcomes or otherwise, is obvious. Simultaneously quantifying disease burden from several causes minimises the tendency to "inflate" the burden from specific conditions viewed in isolation. Moreover, burden of disease studies provide an accounting tool to assess the quality, availability and relevance of data collection systems for the purpose for which they were intended -- namely, to guide and inform public health policy and action. The work of Mathers and colleagues will not only enrich public health debates in Australia, but their methodological advances will be of considerable relevance to similar efforts under way or contemplated elsewhere.

Alan D Lopez
Coordinator, Epidemiology and Burden of Disease
World Health Organization, Geneva, Switzerland
lopezaATwho.ch

1. d'Espaignet E, van Ommeren M, Taylor F, et al. Trends in Australian mortality, 1921-1988. Canberra: Australian Institute of Health and Welfare/AGPS, 1991. (Mortality Series No. 1.)
2. Gold J, Li Y, Kaldor JM. Premature mortality in Australia 1983-1992: the first decade of the AIDS epidemic. Med J Aust 1994; 161: 652-656.
3. Lopez AD. Competing causes of death: a review of recent trends in mortality in industrialized countries. Trends in cancer mortality in industrial countries. Ann N Y Acad Sci 1990; 609: 58-74.
4. Murray CJL, Lopez AD. Progress and directions in refining the global burden of disease approach: a response to Williams. Health Econ 2000; 9: 69-82.
5. Murray CJL, Lopez AD. The Global Burden of Disease: a comprehensive assessment of mortality and disability from diseases, injuries and risk factors in 1990 and projected to 2020. Cambridge, Mass: Harvard University Press on behalf of the World Health Organization and the World Bank, 1996.
6. Mathers CD, Vos ET, Stevenson CE, Begg SJ. The Australian Burden of Disease Study: measuring the loss of health from diseases, injuries and risk factors. Med J Aust 2000; 172: 592-596.
7. Mathers C, Vos T, Stevenson C. The burden of disease and injury in Australia. Australian Institute of Health and Welfare. Canberra: AIHW, 1999. Also at: <http://www.aihw.gov.au/publications/health/bdia.html> (accessed 12 May 2000).
8. Mathers C, Vos T, Stevenson C. The burden of disease and injury in Australia: summary report. Australian Institute of Health and Welfare. Canberra: AIHW, 1999. Also at: <http://www.aihw.gov.au/publications/health/bdiasr.html> (accessed 12 May 2000).
9. World Health Organization. Obesity: preventing and managing the global epidemic. Geneva. World Health Organization, 1998. (WHO/NUT/NCD/08.1.)