Academic journal article Bulletin of the World Health Organization

Cross-National Comparability of Burden of Disease Estimates: The European Disability Weights Project. (Research)

Academic journal article Bulletin of the World Health Organization

Cross-National Comparability of Burden of Disease Estimates: The European Disability Weights Project. (Research)

Article excerpt

Introduction

The value of summary measures of population health as a tool for health policy and planning purposes has been increasingly recognized (1). Summary measures such as the disability-adjusted life-year (DALY) combine mortality data with that on non-fatal health outcomes. In the DALY, as developed in the Global Burden of Disease (GBD) study, mortality and morbidity were included as years of life lost (YLL) and years lived with disability (YLD), respectively (2). Essential information for the estimation of DALYs include disease-specific epidemiological data and disability weights. The latter are used for weighting the years lived with a specific disease by the severity of the disability associated with it. The GBD study inspired the use of DALYs in comprehensive studies on disease burden at the national level (3-5). Both the valuation technique and the use of expert opinion in order to elicit disability weights in the GBD study have been questioned on methodological grounds (6-8). Additionally, the sensitivity of DALYs, defined by the relative contributions of true and error variation, is assumed to be low. Potential sources of true variation include differences in the size and structure of populations, real differences in disease epidemiology between populations or over time, and differences in disability weights. Error variation may originate from sampling and measurement error and from incomparability in available epidemiological data and disability weights. The detection of true variation is the focus of rest when estimating the burden of disease in DALYs. However, error may limit the power to detect true differences between populations (9).

The cross-national stability' of disability weights and the relative effects of three sources of variability on DALY estimates were investigated in the European Disability Weights Project. In this paper we present the derivation of country-specific disability weights for 15 disease stages; analyse cross-national variation in visual analogue scale (VAS) scores for these disease stages; apply the disability weights in a burden-of-disease estimation of dementia in women in Denmark, England and Wales, France, the Netherlands, Spain, and Sweden; and explore the relative importance of cross-national differences in demography, epidemiology, and disability weights.

Methods

The European Disability Weights Project included participants from Denmark, England and Wales, France, the Netherlands, Spain, and Sweden, and ran for two years from March 1998.

The disability weight derivation consisted of the following: disease selection and staging; valuation; and analysis with special attention to country-specific effects.

The burden of disease estimation involved the following: collection of demographic data; collection of prevalence data for dementia; epidemiological modelling; and DALY estimation.

Dementia was chosen because there was evidence that good and comparable epidemiological data were available in the participating countries. Only the results for women are presented because of limited space.

Disease selection and staging

Thirteen diseases were selected which covered a range of severity and different dimensions of disability and were relevant for the European situation. Each was subdivided into homogeneous stages with respect to functional status, treatment, and prognosis. A textual and a standardized generic description of the associated functional health status, validated by clinical experts, was developed for each stage. The generic description used the EuroQol (EQ-5D) classification system of health status (mobility, self-care, usual activities, pain/ discomfort and anxiety/depression), with the addition of a sixth dimension of cognitive functioning (EQ-5D+C) (10, 11). Fig. 1 provides an example of a description of a disease stage as presented to panellists in the valuation procedure.

[FIGURE 1 OMITTED]

Valuation procedure

The valuation procedure, modified from the GBD protocol and the Dutch Disability Weights Study (12, 13), used a panel process to value 15 disease stages, one or two for each selected disease. …

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