Abstract
BackgroundDisability-Adjusted Life Years (DALYs) are an established method for quantifying population health needs and guiding prioritisation decisions. Global Burden of Disease (GBD) estimates aim to ensure comparability between countries and over time by using age-standardised rates (ASR) to account for differences in the age structure of different populations. Different standard populations are used for this purpose but it is not widely appreciated that the choice of standard may affect not only the resulting rates but also the rankings of causes of DALYs. We aimed to evaluate the impact of the choice of standard, using the example of Scotland.MethodsDALY estimates were derived from the 2016 Scottish Burden of Disease (SBoD) study for an abridged list of 68 causes of disease/injury, representing a three-year annual average across 2014–16. Crude DALY rates were calculated using Scottish national population estimates. DALY ASRs standardised using the GBD World Standard Population (GBD WSP) were compared to those using the 2013 European Standard Population (ESP2013). Differences in ASR and in rank order within the cause list were summarised for all-cause and for each individual cause.ResultsThe ranking of causes by DALYs were similar using crude rates or ASR (ESP2013). All-cause DALY rates using ASR (GBD WSP) were around 26% lower. Overall 58 out of 68 causes had a lower ASR using GBD WSP compared with ESP2013, with the largest falls occurring for leading causes of mortality observed in older ages. Gains in ASR were much smaller in absolute scale and largely affected causes that operated early in life. These differences were associated with a substantial change to the ranking of causes when GBD WSP was used compared with ESP2013.ConclusionDisease rankings based on DALY ASRs are strongly influenced by the choice of standard population. While GBD WSP offers international comparability, within-country analyses based on DALY ASRs should reflect local age structures. For European countries, including Scotland, ESP2013 may better guide local priority setting by avoiding large disparities occurring between crude and age-standardised results sets, which could potentially confuse non-technical audiences.
Highlights
Disability-Adjusted Life Years (DALYs) are an established method for quantifying population health needs and guiding prioritisation decisions
The all-cause age-standardised rates (ASR) of DALYs in Scotland directly standardised using the Global Burden of Disease (GBD) WSP was 18,275 per 100,000 population, 26% lower than the ASR using ESP2013
Summary of findings Our study found that the ranking of causes of disease/injury were similar between ranks based on crude rates of DALYs and ranks based on age-standardised rates of DALYs using ESP2013 as the reference population
Summary
Disability-Adjusted Life Years (DALYs) are an established method for quantifying population health needs and guiding prioritisation decisions. A Burden of Disease (BoD) approach can be used to summarise the debilitating effects of morbidity and premature mortality in a population in a consistent and comparable manner This is achieved by framing the effects of morbidity and mortality as population health loss as a function of time, in a composite measure called Disability-Adjusted Life Years (DALYs) [1]. It is essential that estimates used to set national and local policies are based on the needs of the populations they represent and are a valid reflection of the relative burden of different causes of ill-health and mortality. Once this assessment has been made comparability between different locations are other important approaches which can be usefully utilised
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