Disability-adjusted life years (DALYs)

The disability-adjusted life year (DALY) is a generic measure of health effect that can be used in cost-effectiveness analysis as an alternative to the quality-adjusted life year (QALY). Originally developed by the World Bank in 1990, DALYs have been adopted by the World Health Organisation (WHO) as a favoured way of comparing overall health and life expectancy in different countries. They are a measure of overall disease burden, expressed as the number of years lost due to ill-health, disability or early death. One DALY represents one year of health life lost, typically compared with a theoretical maximum life that is free of disability or disease. In some calculations, years of health life are age-weighted, resulting in disability in younger years having a higher overall impact on overall DALY scores. Based on the ‘person trade-off’ technique, disability weights for (seven levels of) conditions have been determined by a panel of experts, and aggregate DALYs lost (globally and by country) have been calculated for a wide range of conditions. Unlike QALYs, DALY weights are not based on population surveys and its components (reduced survival and increased disability) are added, not multiplied. Psychiatric conditions are notable causes of DALYs lost in Western countries due to high disability burden, but not reduced survival.