National Burden of Disease Studies: Apractical Guide
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NATIONAL BURDEN OF DISEASE STUDIES: A PRACTICAL GUIDE Edition 2.0 OOccttoobbeerr 22000011 World Health Organization Global Program on Evidence for Health Policy WHO, Geneva ACKNOWLEDGEMENTS This Manual was prepared by an editorial team comprising Colin Mathers, Theo Vos, Alan Lopez, Josh Salomon, and Majid Ezzati. In preparing this manual, we drew on the experience and publications of the Global Burden of Disease Study, of various national burden of disease studies, and on teaching materials prepared for burden of disease training workshops. Chapter 7 draws heavily on guidelines for epidemiological reviews prepared by Edouardo Sabaté. We thank the many people who have contributed to these, but particularly Chris Murray, who has played a leading role in the development and promotion of burden of disease analysis and methodology and Rafael Lozano who contributed substantially to the Global Burden of Disease project at WHO over the last two years. We also thank Jan Barendregt for development and documentation of the DISMOD II software program, and Abhaya Indrayan for his useful inputs and collaboration in preparation of this manual. Suggested citation Mathers CD, Vos T, Lopez AD, Salomon J, Ezzati M (ed.) 2001. National Burden of Disease Studies: A Practical Guide. Edition 2.0. Global Program on Evidence for Health Policy. Geneva: World Health Organization. CONTENTS 1. INTRODUCTION............................................................................................................................. 1 2. SUMMARY MEASURES OF POPULATION HEALTH ............................................................................. 5 3. DISABILITY-ADJUSTED LIFE YEARS (DALYS) ................................................................................. 9 4. PLANNING A NATIONAL BURDEN OF DISEASE STUDY.................................................................... 16 5. ESTIMATING MORTALITY BY AGE AND SEX AND CALCULATING A LIFE TABLE ................................... 24 6. ESTIMATING CAUSES OF DEATH .................................................................................................. 40 7. EPIDEMIOLOGICAL ESTIMATES – GENERAL APPROACH................................................................. 51 8. DISEASE MODELLING USING DISMOD.......................................................................................... 64 9. HEALTH STATE VALUATION.......................................................................................................... 80 10. SPECIFIC APPROACHES TO THE CALCULATION OF YLD.............................................................. 87 11. CALCULATING DALYS ............................................................................................................. 111 12. CALCULATING HEALTHY LIFE EXPECTANCY .............................................................................. 116 13. COMPARATIVE RISK ASSESSMENT............................................................................................ 120 14. PROJECTIONS......................................................................................................................... 131 15. PRESENTATION AND DISSEMINATION OF RESULTS.................................................................... 134 1 INTRODUCTION 1. INTRODUCTION 1.1 PURPOSE OF THIS MANUAL The purpose of this manual is to provide clear practical advice to people undertaking national or sub-national burden of disease studies using the methods developed for the Global Burden of Disease (GBD) Study (Murray and Lopez 1996a). This manual is not intended to provide detailed conceptual or theoretical background to the development of the measures of population health used in burden of disease analyses, such as DALYs or the rationale for burden of disease studies. For such material, you should refer to the GBD publications, and other published papers on burden of disease analysis (see Section 1.5 below for references and information on where to obtain this material). 1.2 BACKGROUND Precise information about diseases and injuries, their incidences, their consequence, their causation and their trend is more than ever necessary to inform policy-making. In a context where increasingly vocal and well informed people demand more health services and interventions than available resources can finance, decision-makers at all levels are increasingly required to evaluate the impact of health policies, to justify the adoption of new ones and to ensure that information is available for inter-programme comparisons. In 1993 the Harvard School of Public Health in collaboration with The World Bank and WHO assessed the global burden of disease . Aside from generating the most comprehensive and consistent set of estimates of mortality and morbidity by age, sex and region ever produced, GBD also introduced a new metric – disability adjusted life year (DALY) – to quantify the burden of disease. The use of DALY allows researchers to combine in a single indicator years of life lost from premature death and years of life lived with disabilities. In recent years, considerable international effort has been put into the development of summary measures of population health that combine information on mortality and non-fatal health outcomes into a International policy interest in such indicators is increasing. The World Health Organization is now undertaking a new assessment of the GBD for the year 2000. The specific objectives of GBD2000 are: · to quantify the burden of premature mortality and disability by age, sex, and region for 135 major causes or groups of causes; · to analyze the contribution to this burden of selected risk factors using a comparable framework; and · to develop various projection scenarios of the burden of disease over the next 30 years. At the same time, WHO member States are increasingly requesting technical assistance and support to undertake country-level burden of disease measurement. Over 30 countries are in various stages of undertaking these assessments and WHO support to these efforts not only ensures better data for planning but also enables further development and testing of tools to facilitate burden of disease assessments. This iterative process builds a partnership between WHO and Member States, laying the groundwork for tackling the bigger challenge of integrating burden of disease data into country-level programming and health system performance assessment. In addition, this partnership contributes towards the ongoing updating of the 1990 estimates of the global and regional burden of disease to year 2000 estimates. 1.3 NATIONAL STUDIES CARRIED OUT TO DATE With the publication of the original GBD Study in 1993-1996, there was immediate interest in applying the methods in countries. Since 1993, when the study in Andhra Pradesh in India started 35 national burden of disease (NBD) studies have been undertaken. Some have been completed and others are still in progress. 1 1 INTRODUCTION Although the majority have followed the essential principles and methodology initially proposed by Murray and Lopez (1996), they are not totally comparable to each other, because some have important modifications to the original procedures. For example, taking into account the valuation of health states as a criterion for classification of the studies, a first generation of NBD studies can be defined as those which used the map of disabilities published in the original version (Lozano et al 1994, 1995, Fundacion Mexicana Para La Salud 1995, Republica de Colombia Ministerio de Salud 1994, Concha et al 1996, Vos et al 1995). Another group of countries have validated the procedures followed at the international level by undertaking local valuations of health states. Yet another group of studies has developed their own procedures for health valuations (Ruwaard and Kramers 1998, Mathers et al 1999). NBD studies have been undertaken primarily by Ministries of Health (planning or epidemiology departments) or by universities. Some of them have been financed by international agencies like the World Bank and others with local funding. These studies have proved to be of considerable usefulness in guiding health sector reform and for priority setting in countries. 1.4 ORGANIZATION OF CONTENTS The content of this Manual has been organized to reflect as far as possible the sequential steps which need to be followed to carry out a national burden of disease study. Chapters 2 and 3 introduce the reader to the key issues and concepts in the construction of summary measures of population health. A choice of one or more of these measures is required as the basic metric to measure disease burden. This is followed by Chapter 4 on the various elements involved in planning an NBD study, including the set of specific choices that need to me made concerning the level and detail of the analysis. Once these decisions have been made, the first step in carrying out a study is to estimate the age-sex distribution of deaths. Guidance on methods to do this is given in Chapter 5. Chapter 6 then provides details on methods and approaches to estimating causes of death by age and sex. With Chapters 5 and 6, the basic epidemiological material for estimating the premature mortality component of DALYs can be assembled. The next section of the Manual deals with the estimation of disease burden for non-fatal outcomes. Chapter 7 outlines the principles and key data sources needed to prepare systematic reviews of the epidemiological literature in order to estimate basic input parameters for calculating