The Burden of Mental Disorders: A Comparison of Methods between the Australian Burden of Disease Studies and the Global Burden of Disease Study

Article excerpt

Voir page 436 le resume en francais. En la pagina 436 figura un resumen en espanol.

The prominent position of mental disorders, particularly depression, as a cause of disease burden is a widely quoted result of the Global Burden of Disease (GBD) study (1-5). However, there has been little discussion of the methods used to estimate the mental health burden at either the global or national level. The general debate about the use of the disability-adjusted life year (DALY) as a summary measure of population health has largely concentrated on the underlying assumptions of age-weighting and discounting and the relevance of burden of disease measurements to policy-making (6-11).

One report has challenged the severity weights for mental disorders used in the GBD study. Findings from a small community sample in New South Wales, Australia, led to a cautious conclusion that the GBD study may have overestimated the disability weights (DWs) for depression and substance disorders, while underestimating the level of disability associated with anxiety disorders (12). However, the epidemiological assumptions that fed into the GBD study's calculation of the burden of mental disorders have not been scrutinized in the literature. Only three of the intended ten volumes in the Global Burden of Disease and Injury Series have been published to date (13-15); and a description of methods used in calculating the burden of mental disorders has not yet appeared. The only epidemiological information is in vol. 2 of the series, detailing for each disease and world region the age-specific and sex-specific values of incidence, prevalence, average duration and mortality.

As part of the two recent burden of disease studies in Australia, an effort was made to examine critically the GBD estimates for mental disorders, to improve the methods and to apply them to the most appropriate information on the epidemiology of mental disorders in the country. The results of the national Australian study conducted by the Australian Institute of Health and Welfare and of an analysis of the burden of disease in Victoria carried out by the state's Department of Human Services are available as printed reports and on the internet (16-19). The two project teams worked closely together and shared methods and analyses.

The methods used to estimate the burden of mental disorder in Australia are discussed below, and departures from those of the GBD study are identified and justified. The consequences are described and discussed of the methodological changes on the estimates for the state of Victoria and the results are compared with those of the GBD estimates for the Established Market Economy (EME) region. Although burden was estimated for dementia and other neurological conditions in the Australian studies, these conditions were included in a separate category for nervous system disorders and they are not discussed here.

Methods

The disability-adjusted life year

Summary measures of population health combine information on mortality and non-fatal health outcomes to describe population health in a single number. The DALY was designed to provide a common measure for fatal and non-fatal health outcomes, to allow estimates of health impact to be mapped to causes, and to enable common values and health standards to be applied to all regions of the world (13).

DALYs for a disease are the sum of the years of life lost because of premature mortality in the population and the years lost because of disability for incident cases of the health condition in question. The DALY is a health gap measure that extends the concept of potential years of life lost because of premature death to include equivalent years of healthy life lost in states of less than full health, broadly termed disability (20).

The Australian burden of disease studies depart from the general methodology used in the GBD study in the following key areas. …