Disability weights in the global burden of disease 2010 study: two steps forward, one step back?

Perspectives In the global burden of disease (GBD) project, the disability-adjusted life year (DALY) is used as a measure of disease burden. DALYs combine years of life lost to premature death and years lived with a disability or health condition, weighted for the severity of the condition. This combined measure makes it possible to compare health conditions with different symptoms and outcomes using a standardized metric. Initiated in the early 1990s, the methods used to measure the GBD recently underwent major revision. Details about the new methods and up-to-date information about the state of health in the world were published in the December 2012 issue of the Lancet, which was devoted entirely to the GBD 2010 study. 1 Although the new methods used to calculate the GBD are a considerable improvement over previous ones, central concerns about the utility of DALYs for making decisions about the prioritization of health conditions and the allocation of resources remain unaddressed. Since their inception, GBD studies have been criticized for their methodological and normative choices in four areas: the use of age weighting (i.e. the assignment of different weights to years of life lost at different ages); the use of different life expectancies for men and women; discounting (i.e. the assignment of a lower weight to years of life lost in the future); and the determination of disability weights, which are intended to capture the severity of a condition. The team that conducted the GBD 2010 study took these criticisms seriously and enlisted experts in multiple disciplines to help revise its methods. In response to the first three criticisms it dropped discounting, made age weights uniform and used the same life expectancy for men and women (86 years) to calculate years of life lost. 1 To address the fourth criticism, the team revised its method for determining disability weights. These are standardized values that are assigned to non-fatal health outcomes to capture their severity on a scale between 0 (full health) and 1 (death). For example, in the GBD 2010 study, complete hearing loss and severe chronic neck pain were assigned disability weights of 0.033 and 0.286, respectively. Many critics of earlier GBD studies, which were originally commissioned in 1990 and have been updated twice since, were dissatisfied with the particular person trade-off method used to determine disability weights. The method consisted of asking respondents to choose between different hypothetical public health interventions. 2 …