Disability weights in the Global Burden of Disease 2010: unclear meaning and overstatement of international agreement.
The Global Burden of Disease Project (GBD) is a huge international enterprise that provides vast amounts of valuable data on (a) the prevalence of different diseases in the world as a whole, in regions and in individual countries, (b) their causes (risk factors), and (c) their burden on populations in terms of Disability Adjusted Life Years (DALYs). However, the methods used for disability weighting of life years are problematic. After a long history of changing concepts and methods the GBD in its 2010 version has landed on 'health' as a unidimensional construct to be used for weighing multi-dimensional non-fatal health problems against each other and against death. The unidimensional health construct does not have a clear meaning. It likely also leads to biases in assessments of conditions that in everyday language are associated with 'being ill' as opposed to conditions which are not associated with 'being ill' (states of physical disability and the state dead). Furthermore, the transformation of ordinal data from paired comparisons into disability weights with purported ratio scale properties is not validated nor explained in a way that allows judgements of face validity. There are also issues related to the way in which different health problems were described to respondents. Lastly, international agreement on disability weights is clearly overstated. Policy makers at national and international levels should understand the GBD 2010 methods properly and carefully consider their validity before deciding to implement the methods, or the disability weights estimated so far by means of them, in further projects and studies. Considerable local adjustments of the weights offered presently are a likely outcome of such methodological scrutiny.