Burden of Disease

Burden of disease is the impact of a health problem in an area measured by financial cost, mortality, morbidity, or other indicators. It is often quantified in terms of quality-adjusted life years (QALYs) or disability-adjusted life years (DALYs),which combine the burden due to both death and morbidity into one index.

The global burden of disease (GBD) is a comprehensive regional and global assessment of mortality and disability from 107 diseases and injuries and ten risk factors. The GBD is assessed using the GBD study by the World Health Organization, and is an example of an evidence-based input to public health policy debate. The aim of the study was to provide information and projections about disease burden on a global scale. 公卫论坛

The burden of disease can be viewed as the gap between current health status and an ideal situation in which everyone lives into old age free of disease and disability. Causes of the gap are premature mortality, disability and exposure to certain risk factors that contribute to illness. 公卫论坛

The GBD is now in its fifth round. The series quantifies the burdens of 483 sequelae of 109 major causes of death and disability disaggregated by eight geographic regions and ten age-sex groups.

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2.1 Definition
One DALY can be thought of as one lost year of "healthy" life. The sum of these DALYs across the population, or the burden of disease, can be thought of as a measurement of the gap between current health status and an ideal health situation where the entire population lives to an advanced age, free of disease and disability.

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2.2 Calculation
DALYs for a disease or health condition are calculated as the sum of the Years of Life Lost (YLL) due to premature mortality in the population and the Years Lost due to Disability (YLD) for incident cases of the health condition: 公卫家园

DALY = YLL + YLD 公卫百科

The YLL basically correspond to the number of deaths multiplied by the standard life expectancy at the age at which death occurs. The basic formula for YLL (without yet including other social preferences discussed below), is the following for a given cause, age and sex:

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where: 公卫人

YLL = N * L

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N = number of deaths
L = standard life expectancy at age of death in years
Because YLL measure the incident stream of lost years of life due to deaths, an incidence perspective is also taken for the calculation of YLD. To estimate YLD for a particular cause in a particular time period, the number of incident cases in that period is multiplied by the average duration of the disease and a weight factor that reflects the severity of the disease on a scale from 0 (perfect health) to 1 (dead). The basic formula for YLD is the following (again, without applying social preferences):

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where:

YLD = I * DW * L

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I = number of incident cases
DW = disability weight
L = average duration of the case until remission or death (years)

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