a Institut de médecine sociale et préventive, Faculté de médecine, Université de Genève, 1211 Geneva 4, Switzerland.
b Departamento de Salud Internacional, Escuela Nacional de Sanidad, Instituto de Salud Carlos III, 28029 Madrid, Spain.
Reprint request to: Dr Doris Schopper, Institut de médecine sociale et préventive, Faculté de médecine, Université de Genève, 1211 Geneva 4, Switzerland. E-mail: dschopper{at}geneva.msf.org
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Abstract |
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Methods We followed the procedures developed for the Global Burden of Disease (GBD) study to ensure comparability. Some adaptations were made for mortality coding. Disability was estimated based on data for countries classified as Established Market Economies (EME) in the GBD study.
Results Non-communicable diseases accounted for 79% of the disability adjusted life years (DALY), injuries represented 12%, and communicable diseases and other disorders 9%. Ischaemic heart disease was the largest single contributor to DALY, followed by unipolar major depression. Neuropsychiatric disorders and mental health accounted for more than 23% of DALY.
Conclusions Some of the most important problems identifieddepression, osteoarthritis and alcohol abusewould have been overlooked in an analysis based solely on mortality data. The most striking finding is the importance of mental health problems. The main limitation is the lack of morbidity data for Geneva.
Keywords DALY, YLD, YLL, health priorities, burden of disease, Switzerland
Accepted 17 February 2000
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Introduction |
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Traditionally mortality-based indicators such as life expectancy and infant mortality have been used to measure changes in the health status of a population. In addition, specific mortality rates have been used to identify health problems that needed special attention. To take account of the fact that it may be natural to die at a certain age, and that a death at age 80 should not be valued in the same way when setting health priorities as a death at age 20, the concept of premature death* was developed.48 However, in industrialized countries where mortality rates are low, these are no longer sensitive indicators of change. As life expectancy is already very high, major changes in health status would need to occur to induce a measurable change in life expectancy. In Geneva, for example, we estimated that even if all deaths before age 50 were eliminated, life expectancy would only increase by 3.8 years for men and 2.1 years for women. If all deaths before age 70 were eliminated, life expectancy would increase by 8.3 years for men and 4.7 years for women. In countries with high life expectancies the issue is thus not so much to add quantity to life, but quality. Low and non-fatal consequences of acute and chronic disease and injury become as or more important than premature mortality.
We thus wanted to use a synthetic indicator which combines fatal and non-fatal outcomes. Based on earlier attempts to develop a summary measure that combines mortality, morbidity and disability,912 such an indicator was elaborated for the 1993 World Development Report Investing in health:13 the disability adjusted life year (DALY).14 The DALY extends the concept of premature death (potential years of life lost [PYLL]) to include equivalent years of healthy life lost because of illness and disability (years lived with disability [YLD]).15 The methods developed for this worldwide analysis are being used in studies in The Netherlands, Spain, Sweden, Australia and the USA,16 although results have not been published yet.
We used the DALY method to identify the relative importance of specific diseases and injuries in the overall disease burden in the canton of Geneva. We describe the methodological adaptations needed for the specific situation in Geneva, present the results of the analysis by age group and sex, discuss the relative importance of specific health problems and identify the 15 most important problems. Major differences between the burden of disease in Geneva and other industrialized countries will be indicated. Finally, we discuss the relevance of these findings for the future health strategy in the canton of Geneva.
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Materials and Methods |
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Mortality data
Mortality estimates came from the national 19901994 mortality data base for the canton of Geneva, the most recent data available at the time of the study. Data were averaged over the 5-year period to avoid unstable mortality rates due to the small population (400 000). In Switzerland information on cause of death is coded according to the 8th Revision of the International Classification of Diseases (ICD-8), while DALY were developed using mainly the ICD-9 classification. Therefore coding was revised to ensure comparability. Differences were found in the coding of viral hepatitis B and C, which were aggregated into a single category as infectious hepatitis.
Following the GBD systematic, health problems were ordered in a tree structure with three basic causes of death: communicable diseases and maternal, perinatal and nutritional disorders (Group I); non-communicable and chronic illnesses (Group II); and all injuries, intentional and non-intentional (Group III). Each group is divided into major subcategories that are mutually exhaustive and exclusive and which can be disaggregated into a third and fourth level to identify more specific causes of death.22
Irrelevant diseases such as most tropical diseases were excluded. Others that are very rare were not disaggregated at the third level (drowning). Three new subcategories were added due to the relative importance of the disease entities in Geneva: cancer of the larynx, sudden infant death and influenza with or without pneumonia. Finally, due to aggregated coding of prematurity and low birthweight in Geneva, both are included in the same subgroup, instead of using exclusively low birthweight as noted in the GBD classification.
To deal with ill-defined codes, we assumed that deaths due to injuries were not likely to be coded as an ill-defined cause; that in adults, ill-defined deaths are more likely to be due to deaths from chronic diseases than from transmissible diseases; and that in children, these deaths are probably due to diseases from Groups I or II. Based on these assumptions all deaths with ill-defined codes in adults were redistributed to Group II and in children to Groups I and II, proportionally to the existing deaths in each age and sex group.
With regard to cardiovascular diseases, coding for cerebrovascular disease is mostly correct or slightly overestimated while ischaemic heart disease (IHD) is more likely to be undercoded due to excessive coding of heart failure, ventricular dysrhythmias, general arteriosclerosis, and ill-defined descriptions and conditions of heart disease. These codes are termed cardiovascular garbage codes. Based on the algorithm used in the GBD23 we partially recoded ill-defined cardiovascular deaths to IHD.
Mortality analyses are based on standard model life table West 26,24 with a life expectancy at birth of 82.5 years for women. Life table West 2525 for females is used for men (life expectancy at birth of 80 years). Thus deaths at all ages will be considered as a loss and included in the analysis, with a slight difference in the standard for males and females. For reasons of comparability we used the same age-weighting and discounting of future years (3%) as Murray et al.26
Disability data
The information required to estimate Years Lived with Disability (YLD)disease incidence by age and sex, age of disease onset, disease duration in years, and degree of disabilityis not available for Geneva in most cases. We thus indirectly estimated the YLD using data published by Murray et al. for the 35 countries classified as Established Market Economies (EME).17,22 We used YLD/YLL (years life lost) ratios calculated for health conditions in EME to estimate YLD in Geneva when this ratio is <10 (i.e. AIDS, self-inflicted injuries/suicide). In conditions with a higher disability burden (YLD/YLL ratios >10; i.e. depression, osteoarthritis) we used primary data on incidence, age of onset, duration and degree of disability for EME countries as published in the GBD to calculate YLD in Geneva.
Throughout the study, EME estimates were validated for diseases for which information on disease incidence or prevalence was available for Geneva. Regarding unipolar major depression, one population-based survey had found higher incidence rates than the EME estimates.27 As these data have not yet been confirmed by an epidemiological study, we used the more conservative EME estimates. Following consistent findings that dementia prevalence is higher in Geneva than in EME,28 we increased the dementia incidence estimate for EME by 10% to calculate YLD. No other disease estimates were adjusted.
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Results |
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Conclusion |
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This has been the first attempt to identify the most important health problems in the canton of Geneva using DALY as a single unit of measurement. Combining mortality, morbidity and disability allowed for comparisons between specific health conditions that would not be comparable otherwise. Some of the most important problems identifieddepression, osteoarthritis, alcohol abuse and injuries from fallswould have been overlooked in an analysis based solely on mortality data, as more than two-thirds of the weight of each of these diseases is represented by disability. However, some of the assumptions underlying the method such as age weighting, discount rates and the valuation of disabilities have been challenged.3133 It is probable that age weighting, which reflects a higher valuation of life in early adulthood than in young children and old people, and discount rates reflecting social time preferences, do not influence the list of priority health problems in any major way. In fact the sensitive analysis carried out in the GBD study showed that modifying these specific values did not affect the ranking of importance of the main diseases. However, as pointed out recently,34 the valuation of life lived with disability remains an unsolved problem. Valuing life lived with disability less than a healthy life could lead to discriminate strongly against patients who have less potential for health than others. We would suggest that the priorities identified through the DALY analysis be first compared to locally available evidence and then be used to highlight areas that need special attention. We believe the main limitation of this analysis is the lack of morbidity data for Geneva which forced us to rely on estimates for the EME. Consequently, the comparison with the results for EME as published in the GBD is mostly driven by differences in mortality patterns. The study thus points to the need for consistent long-term data collection, particularly for those conditions where mortality plays a minor part in the attributable disease burden. Meanwhile these first results can serve as baseline against which the future evolution of the health status of the Genevan population can be compared in a more complete way than using only mortality data. In addition, once results from DALY analyses carried out in other European regions become available, similarities and differences should be examined in more detail.
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Appendix |
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Acknowledgments |
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Notes |
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** First proposed by Demsey in 1947, a wide array of different measures have since been elaborated. The simplest and most widely used measure is potential years of life lost. A potential limit to life is chosen arbitrarily (in general close to life expectancy of the population considered) and the duration of life lost due to death is the potential limit minus the age at death.
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