Composite measures of environmental burden of disease at the global level
Seminal studies commissioned by The World Bank in the 1990s led to multiple approaches to assessing how much the modifiable environment contributes to the disease burden. The two major methodological approaches to quantify the health of populations and the burden of disease globally and regionally are (1) exposure-based methods and (2) expert opinion-based methods. In exposure-based methods the relationships between exposure and response to specific risk factors are defined through epidemiologic studies and the estimated attributable fractions are used to generate disease burden expressed quantitatively. The Disability-Adjusted Life Years (DALYs), a composite measure of morbidity and mortality associated with risk factors, is a widely used has become a universal index of disease burden. Detailed assessment of disease burden using this approach has been produced for at least six environmental risk factors and five occupational risk factors at the global level. Expert opinion-based methods rely on systematic literature reviews and surveys of experts across disciplines and geopolitical regions, who are asked to judge which fraction of the total burden of disease can be attributed to environmental a specific factors. This approach has been used to estimate the fraction of disease burden that can be attributed to the environment within 85 out of 102 major disease categories identified by World Health Organization (WHO). While global burden of disease quantifies the amount of disease due to specific causes, global Environmental Burden of Disease (EBD) estimates which fraction of the total burden of disease can be attributed to environmental risks. Studies based on both methods have revealed considerable disparities across regions and countries in the Environmental Burden of Disease (EBD), ranging from one-tenth to more than two-thirds of the total burden of disease that can be prevented through improving environmental quality. These differences are not only caused by actual dissimilarities in underlying environmental quality, but also by differences in calculation approaches and assumptions made.