Disability-adjusted life years

Construction of a composite measure of health that reflects both mortality and morbidity requires a metric – a unit with which to measure health. The unit used by burden of disease studies is time measured in years – the healthy life-year.

Other possible metrics can be envisaged, for example the monetary value of the healthy life lost to disease. Such a metric would share the difficulties encountered in using life-years as a metric and involve additional assumptions and value judgements. On the other hand, it could provide the basis for the calculation of outcome measures for use in cost benefit analyses of the return on investments in improving health as opposed to other sectors. It will not be considered further here.

Years of healthy life can be used as a metric to measure either the length of healthy life or the health gap, which is to say the loss of healthy life in a population compared with some target. While the first type of measure is of value for comparing the health of different populations, the second type provides a more intuitive way of quantifying the negative impact on health of different diseases.

Thus, the core indicator used in studies of the burden of disease is a measure of loss of healthy life. It is the disability-adjusted life year or DALY.