Deaths and hospitalisations attributable to health risks

Estimates of the numbers and rates of deaths and hospitalisations attributable to the use of tobacco and alcohol, to overweight and obesity and other risk factors used age and sex-specific aetiologic fractions for NSW developed by the Australian Institute of Health and Welfare (AIHW) as part of the Australian Burden of Disease Study 2015 (ABDS 2015). The term "population attributable fraction" is a synonym for 'aetiological fraction'. An aetiological fraction is the estimated proportion of cases of the disease in a specific population that would be eliminated in the absence of the risk factor. Hospitalisations attributable to risk factors measure only the more severe outcomes of these risk factors and exclude less severe morbidity which may be captured elsewhere such as in primary health care data.

The ABDS 2015 identified 38 risk factor components that were combined, resulting in 18 individual risk factors which can broadly be grouped into categories (behavioural, metabolic, environmental and dietary risks). Details of the methods used in the ABDS 2015 to derive age and sex-specific aetiological fractions can be found in the report Australian Burden of Disease Study 2015: methods and supplementary information. Below is an overview of the methods from the report (p 111-12).

The burden attributable to selected risk factors is generally estimated using population attributable fractions (PAFs) applied to the disease burden estimated in the ABDS 2015. If PAFs appropriate to the disease and population in question are available from a comprehensive data source (such as a disease register), they are applied directly. If not, PAFs are estimated using the following process:

1. Select risk factors.

2. Identify linked disease based on best evidence in the literature that risk factor has a causal association with increased prevalence or mortality.

3. Define the risk factor exposure level not associated with increased risk of disease (i.e. theoretical minimum risk exposure - TMRED).

4. Estimate the PAFs by comparative risk assessment method (Lim et al. 2012).

5. Estimate the effect of risk factors on disease outcomes (relative risks).

6. Estimate the population-level distribution of risk factor exposure.

7. Calculate the population attributable fraction. This is done for each risk-outcome pair by sex and age group.

The AIHW provided the Australian fractions to NSW with mapping of diseases to ICD-10 codes. These were applied to death and hospital unit record files for these indicators.

References

Australian Institute of Health and Welfare. Australian Burden of Disease Study: Impact and causes of illness and death in Australia 2015 - summary report. Australian Burden of Disease Study series no. 18. BOD 21. Canberra: AIHW; 2019.

Australian Institute of Health and Welfare. Australian Burden of Disease 2015: methods and supplementary material. Australian Burden of Disease Study series no. 20. Cat. no. BOD 23. Canberra: AIHW; 2019.

Lim SS, Vos T, Flaxman AD, Danaei G, Shibuya K, Adair-Rohani H et al. A comparative risk assessment of burden of disease and injury attributable to 67 risk factors and risk factor clusters in 21 regions, 1990-2010: a systematic analysis for the Global Burden of Disease Study 2010. Lancet 2012; 380(9859): 2224-60.