At the population level, the burden of disease as measured by DALYs is calculated by DALY = YLL + YLD where YLL is years of life lost, and YLD is years lived with disability. In turn, population YLD is determined by the number of years disabled weighed by level of disability caused by a disability or disease using the formula YLD = I x DW x L. In this formula I = number of incident cases in the population, DW = disability weight of specific condition, and L = average duration of the case until remission or death (years). There is also a prevalence (as opposed to incidence) based calculation for YLD. Premature death is calculated by YLL = N x L, where N = number of deaths due to condition, L = standard life expectancy at age of death (expectancy - age at death).[4]