Environmental burden of disease calculation
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Environmental burden of disease calculation
This chapter provides information about methods to calculate the environmental burden of disease, and the assumptions and choices that need to be made. Table 2-1 provides an overview of these baseline assumptions underlying the calculations as performed in the EBoDE project. The remainder of this chapter describes the specific models used for calculating the EBD and explains the different parameters and data used.
TABLE 2-1. Baseline facts and assumptions underlying environmental burden of disease calculations as carried out in the EBoDE project.
| Parameter of assumptions | Choise made | Motivation | Remarks | |
| Year | 2004 | Most redcent year with relatively good data availability | Exposure trends were evaluated till 2010 for a qualitative policy analysis | |
| Environmental stressors | Benzene, dioxins (including furans and dioxin-like PCBs), second-hand smoke, formaldehyde, lead, noise, ozone, particulate matter (PM) and radon | |||
| Countries | Belgium, Finland, France, Germany, Italy and the Netherlands | Integration of national projects | EBoDE working group and methodology is open for other countries | |
| Age weighing & discounting | Main results without discounting and age-weighing; alternative results with discounting (3%) and age-weighing (standard) | Ethical reasons. Supplementary discounted and age-weighed results presented for comparability with WHO estimates | ||
| Standard Life Expectancy | 80 years for men and 82.5 for women | Comparability with WHO estimates | ||
| Lag time | Calculations carried out with and without lag times | For certain diseases there is a relatively long lag between exposure and the effect. When using discounting, the lag should be accounted for | Lag times are based on author judgement and serve as rough estimates | |
| Uncertainty analyses | Qualitative and partly quantitative | It is essential to assess whether the substantial inherent uncertainties affect the order of magnitude of the results or the ranking of stressors | Data availability and limited resources allowed only for qualitative approach. Additional quantitative analyses are recommended as a part of follow-up research |
Basic calculation of the environmental burden of disease
The DALY measures health gaps (i.e. years of life lost due to death or disability) as opposed to health expectancies. It measures the difference between a current situation and an ideal or alternative situation. The DALY combines the time lived with disability and the time lost due to premature mortality in one measure:
DALY = YLL + YLD
where: YLL = Years of Life Lost due to premature mortality. YLD = Years Lost due to Disability.
Years of Life Lost (YLL) in a case of individual death is calculated as the difference between the standard life expectancy at the age of death and the actual age at death. When population data is tabulated for age categories, YLL can be calculated as:
L = LE (agedeath, gender) -agedeath
The basic formula for calculating
the population-wide YLL is:
YLL = N x L
where: LE(age,gender) = life-expectancy at age of death, accounting for gender agedeath = age at death N = number of deaths in a given age category L = remaining years to standard life expectancy at age of death (in years).
Methods for calculating YLL are
further described in section Years of Life Lost, co-morbidity and multi-causality
To estimate the Years Lost due to Disability (YLD), the number of disability cases is multiplied by the average duration of the disease and a disability weight (see further discussion below). The basic formula is:
YLD = n x DW x L
where: YLD = Years Lost due to Disability n = number of incident cases. DW = disability weight. L = average duration of disability (years)
The formulas above describe undiscounted, non-weighted DALYs. DALYs are sometimes attributed a discounting rate, and weightings according to age, in which case the formulas become more complex. These so-called social preferences are discussed in section 2.3.
==Disability weights== (DW)
Disability weights are used to make different health effects with varying degrees of severity comparable. They are weight factors that reflect the severity of the disease on a scale from 0 (perfect health) to 1 (equivalent to death). These factors have been determined in expert panels using standardized surveys.
==Duration estimates== (L) Besides disability weights, estimates of DALYs for morbidity (Years Lost due to Disability – YLD) also take into account the duration of the disease derived from health statistics, registries, expert judgments, etc. In some cases, prevalence data are used in burden of disease calculations instead of incidence data. In that case, the duration of disease is set to 1 year in the calculation, assuming a steady-state situation in which prevalence equals incidence times duration. For mortality, the duration estimate equals the YLL (Years of Life Lost, see section 2.2).