Global Burden of Disease
The term “burden of disease” can refer to the overall impact of diseases and injuries at the individual level, at the societal level, or to the economic costs of diseases. Specifically, the “global burden of disease” (GBD) refers to a WHO and World Bank study published in the World Development Report 1993 that measured the total loss of health resulting from diseases and injuries. Updated in 1996 and again in 2000, the study generates the most comprehensive and consistent set of estimates of mortality and morbidity by age, sex and region. The original report showed that infectious disease accounts for 43% of the global burden.
The GBD study also introduced a new metric disability-adjusted life year (DALY) to quantify the burden of disease. DALYs are used to help measure the burden of disease and the effectiveness of health interventions. The DALY is a health gap measure, which combines information on the impact of premature death, and of disability and other non-fatal health outcomes. Also statistically innovative are years of life lost (YLLs), an indicator showing loss from premature mortality, based on early death judged against the average life expectancy in the population of a developed country. Thus the burden of disease is a measurement of the gap between current health status and an ideal situation where everyone lives into old age, free of disease and disability.
In the World Health Report 2000, WHO introduced the disability-adjusted life expectancy (DALE), a summary measure of the level of health attained by populations. The name of this measure was changed to health-adjusted life expectancy (HALE) in the World Health Report 2002, to better reflect the inclusion of all states of health in the calculation. The HALE is based on life expectancy at birth but includes an adjustment for time spent in poor health. It is most easily understood as the equivalent number of years in full health that a newborn can expect to live, based on current rates of ill health and mortality.
The Commission on Macroeconomics and Health used burden of disease statistics to show that ill-health among the poor is the result of a relatively small number of identifiable conditions - HIV/AIDS, malaria, TB, childhood infectious diseases, maternal and perinatal conditions, tobacco-related illnesses and micro-nutrient deficiencies.
DALYs and HALE may be used to inform priority-setting. This is a process by which policy makers rank health problems by order of potential for health gain (determined jointly by the disease burden and the cost-effectiveness of available interventions) and allocate funds accordingly, also taking into account other social goals such as reducing health inequality. For example, in some countries, five out of the ten leading causes of DALYs are related to reproductive ill-health, suggesting that this should be a priority in these countries, assuming the existence of cost-effective interventions. Some are concerned that this approach leads to a focus on a single disease or group of diseases, with the result that complementary efforts required to strengthen public health systems are neglected. However, GBD analysts have never suggested that burden alone should be used to set priorities.