ArticlesGlobal and regional mortality from 235 causes of death for 20 age groups in 1990 and 2010: a systematic analysis for the Global Burden of Disease Study 2010
Introduction
Cause-specific mortality is arguably one of the most fundamental metrics of population health. The rates and numbers of people who die, where, at what age, and from what, is a crucial input into policy debates, planning interventions, and prioritising research for new health technologies. Trends in causes of death provide an important geographical summary of whether society is or is not making progress in reducing the burden of premature (and especially avoidable) mortality and where renewed efforts are needed. If a health information system is not providing timely and accurate information on causes of death by age and sex, major reforms are required to provide health planners with this essential health intelligence.
Despite the importance of tracking causes of death and the tradition since 1893 of standardisation of definitions and coding for causes of death in the International Classification of Diseases and Injuries (ICD), global assessments of causes of death are a major analytical challenge. Vital registration systems that include medical certification of the cause of death captured about 18·8 million deaths of an estimated annual total of 51·7 million deaths in 2005, which is the latest year for which the largest number of countries (100) reported deaths from a vital registration system. Even for these deaths, the comparability of findings on the leading causes of death is affected by variation in certification skills among physicians, the diagnostic and pathological data available at the time of completing a death certificate, variations in medical culture in choosing the underlying cause, and legal and institutional frameworks for governing mortality reporting.1, 2, 3, 4, 5 For the remaining deaths that are not medically certified, many different data sources and diagnostic approaches must be used from surveillance systems, demographic research sites, surveys, censuses, disease registries, and police records to construct a consolidated picture of causes of death in various populations. Because of the variety of data sources and their associated biases, cause of death assessments are inherently uncertain and subject to vigorous debate.6, 7, 8
Efforts to develop global assessments for selected causes began in the 1980s.9, 10, 11 These efforts were motivated partly because the sum of various disease-specific estimates substantially exceeded the estimated number of deaths in the world, particularly for children.12 Lopez and Hull11 attempted to develop a set of estimates of mortality in children younger than 5 years (under-5 mortality) by cause consistent with all-cause mortality data in 1983. The Global Burden of Disease study 1990 (GBD 1990) was the first comprehensive attempt to do so, and included 134 causes covering all age groups. The GBD 1990 cause of death approach was applied with some refinements to yield estimates of causes of death for 1999, 2000, 2001, 2002, 2004, and 2008.13, 14, 15, 16, 17 Over this period, special attention was paid to priority diseases such as malaria, HIV/AIDS, and tuberculosis. The Child Health Epidemiology Reference Group (CHERG) also produced estimates of under-5 mortality from 16 causes that summed to estimates of deaths in children younger than 5 years for 2000–03, 2008, and 2010,18, 19, 20 partly using the GBD 1990 approach combined with other methods, and putting special emphasis on the use of verbal autopsy as a source of data in low-income settings. Additionally to these comprehensive approaches, the tradition of disease-specific analyses that began in the 1980s with global cancer mortality has continued and intensified. In the past 5 years, for example, articles and reports have been published on global mortality from maternal causes,21, 22, 23, 24 malaria,25, 26 tuberculosis,27, 28 HIV/AIDS,29 road traffic accidents,30 site-specific cancers,31, 32 and diabetes,33 among others.34, 35 These assessments of individual causes are based on diverse epidemiological approaches of varying scientific rigour, and, moreover, are not constrained to sum to estimates of all-cause mortality from demographic sources.
Global cause of death assessments can be characterised in four dimensions: the universe of raw data identified and examined, efforts to evaluate and enhance quality and comparability of data, the statistical modelling strategy, and whether causes of death are constrained to sum to all-cause mortality. First, in terms of the universe of data, the various iterations of the GBD and CHERG analysis of deaths in children younger than 5 years have made substantial use of data on causes of death from systems that attempt to capture the event of death. Other single-cause analyses, such as the annual UNAIDS efforts to estimate HIV-related deaths, measles estimates,34 the World Malaria Report,26 the WHO Global TB Control Report,28 and many others have used data on disease incidence or prevalence and on case-fatality rates combined in a model of natural history progression. Second, perhaps the area of greatest variation in the published studies is the efforts to assess and enhance the quality and comparability of available data. These efforts often include very specific steps undertaken for different data sources and are frequently poorly documented. Third, in the past two decades, efforts to develop statistical models for causes of death have become more sophisticated. Compositional models that estimate cause fractions for several causes at once were first applied to global health by Salomon and Murray36 and have been used extensively by CHERG but only for a subset of causes. GBD revisions for 1999, 2000, 2001, 2002, 2004, and 2008 have used these compositional models to allocate deaths according to three broad cause groups: communicable, maternal, neonatal, and nutritional causes; non-communicable diseases; and injuries. More recently, the array of modelling strategies used for causes of death has been broadened to include spatial-temporal Gaussian process regression,22, 37 mixed effects hierarchical models, and ensemble models.38 Given the profusion of statistical modelling options, an important innovation has been the reporting of out-of-sample predictive validity to document the performance of complex models.22, 38
Finally, in view of the developments in the field of mortality and cause of death estimation, for the GBD 2010 we completely re-evaluated all aspects of the GBD analytical strategy, including demographic estimation of all-cause mortality.39, 40 Because of the huge increase in published verbal autopsy studies and the availability in the public domain of cause of death data from government vital registration sources (130 countries), the universe of data has expanded substantially. Assessing and enhancing the quality and comparability of data can now take into account time trends in cause of death data from 1980 to 2010 that provide important insights into changes in certification and coding. Borrowing from other scientific fields, we have changed our analytical approach (see below) to an ensemble modelling strategy to generate more realistic uncertainty intervals (UIs) and more accurate predictions.38 These innovations have been used in estimating mortality for an expanded GBD 2010 cause list of 291 causes compared with 134 in the GBD 1990 Study; of the 291 causes, 235 are causes of mortality, whereas the remaining causes account for years lived with disability (YLDs) but not deaths. We use a unified framework for all causes such that the sum of cause-specific estimates equals the number of deaths from all causes in each country or region, period, age group, and sex. This creates a link between the systematic analysis of data on all-cause mortality reported by Wang and colleagues40 and results by cause presented here. In this Article, we provide a summary overview of the vast array of data and methods that have gone into this revision of the GBD, as well as what we believe are the key global and regional findings of importance for health priority debates.
Section snippets
Methods
Some general aspects of the analytical framework such as the creation of the 21 GBD regions and the full hierarchical cause list including the mapping of the ICD to the GBD 2010 cause list are reported elsewhere.39 Although results are reported in this Article at the regional level for 1990 and 2010, the cause of death analysis has been undertaken at the country level for 187 countries from 1980 to 2010. Use of longer time series improves the performance of many types of estimation models; data
Results
The GBD 2010 cause list divides causes into three broad groups. At the most aggregate level, communicable, maternal, neonatal, and nutritional causes account for 13·2 million (24·9%) of 52·8 million total deaths at all ages in 2010. Non-communicable causes account for 34·5 million or 65·5%. The third category, injuries, accounts for 5·1 million or 9·6%. The continued decrease in deaths from communicable, maternal, neonatal, and nutritional disorders is striking, if not surprising. The number of
Discussion
The GBD 2010 is the most comprehensive and systematic analysis of causes of death undertaken to date. The addition of time trends over 1980–2010 and quantification of uncertainty increases both the utility and the methodological rigour of the results. The global health community can now draw on annual estimates of mortality, by age and sex, for 21 regions of the world, for each year from 1980 to 2010, for 235 separate causes, each with 95% UIs to aid interpretation. These estimates of cause of
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