Based on Australian Burden of Disease Study 2015, Australian Institute of Health and Welfare. Prepared by the Centre for Epidemiology and Evidence, NSW Ministry of Health.
Years of life lost (YLL): measures in years the burden from dying 'prematurely', that is dying before the 'ideal' lifespan. The 'ideal' remaining life expectancy varies by age group and gender. YLL represents the fatal component of the total burden of disease in a population.
Years lived with disability (YLD): measures in years the burden from living with ill-health thorugh disease, injury or disability, that could have been in good health. It represents the duration of time spent living with illness, weighted for the severity of the illness. YLD represents the non-fatal burden of disease in a population.
Disability-adjusted life years (DALY): measures in years healthy life lost, either through premature death (YLL) or living with ill health due to illness or injury (YLD). One DALY therefore represents one lost year of healthy life. Total burden (DALY) is the sum of fatal burden (YLL) and non-fatal burden (YLD).
Health-adjusted life expectancy (HALE): the average life expectancy spent in full health. For each disease group, HALE is interpreted as the average life expectancy free of that disease type. Note that some diseases with higher case fatality rates (i.e. a higher death rate closely following initial diagnosis) may have a higher HALE than other chronic diseases where a longer time is spent living in ill health prior to death. It is important to consider the burden due to years of life lost (YLL) for these fatal diseases, since HALE only captures the burden of living with disease.
Please see Australian Burden of Disease Study 2015: methods and supplementary information for more details
Burden of disease analysis measures the combined impact in the entire population of living with illness and injury (non-fatal burden) and dying prematurely (fatal burden). More than merely counting deaths and disease prevalence, it takes into account age at death and severity of disease. The summary measure 'disability-adjusted life years' (or DALY) is used to count the total years of healthy life lost from death and illness in the whole population.
Information on the health impacts and distribution of different diseases and injuries is important for monitoring population health and in providing an evidence base to inform health-policy and service planning. Burden of disease information can also be used to measure the health impact of interventions, and to highlight which diseases to focus on when investigating the cost-effectiveness of programs and interventions.
The Australian Burden of Disease Study 2015 is based on methods developed for the “Global Burden of Disease” studies but has evolved to produce estimates that more accurately reflect the Australian context. The indicators presented here relate to the NSW population for 2011 and 2015 respectively.
Key findings for New South Wales in 2015 included:
-People living in New South Wales lost 1.53 million years of healthy life due to living with or dying early from disease and ill health, which was a 6% increase from 2011.
-The burden due to premature death (50.1% of total burden) was very similar to that of burden from living with illness (49.9%).
-Males experienced more health loss (53% of total burden) than females (47% of total burden).
-The top 5 conditions causing the most burden were cancer and other neoplasms, cardiovascular disease, mental and substance use disorders, musculoskeletal conditions and respiratory disease.
-Health-adjusted life expectancy (HALE) for males and females born in 2015 was 71.6 and 74.5 years, respectively. On average, it is expected approximately 89% of their life will be lived in full health.
Please see Australian Burden of Disease Study: impact and causes of illness and death in Australia 2015 for further details.
Estimating the fatal burden (YLL)
The first step to estimate YLL is to compile the total number of deaths by age and disease (cause of death). All deaths data used in Australian Burden of Disease Study 2015 (ABDS 2015) were extracted from the Australian Institute of Health and Welfare's (AIHW) National Mortality Database. This is a register of all deaths in Australia since 1964, sourced from the cause of death unit record files created by the Australian Bureau of Statistics (ABS).
YLL for each disease is then calculated at the disease-specific level (for each age). Using single year of age at death, each death is weighted according to the remaining or potential life expectancy at that age of death using the reference life table – this becomes the years of life lost. The ABDS 2015 uses the standard reference life table used in Global Burden of Disease Study 2010 and 2013 when calculating YLL for the Australian, subnational and Indigenous populations.
Estimating the non-fatal burden (YLD)
The first step to estimate YLD is to define the major disabling sequelae associated with each disease in the disease list, and attribute disability weights that express the health loss on a scale from 0 (no health loss) to 1 (total health loss) associated with each sequelae. Several sequelae may be associated with each disease. To provide a set of weights for these sequelae, ABDS 2015 has followed the practice of using estimates of the health losses associated with a smaller set of health states to which each of the sequelae can be mapped. The health states and disability weights used in this study for both national and Indigenous estimates are drawn from Global Burden of Disease Study 2013.
The next step is to compile estimates of point prevalence for each sequela-health state combinations. An adjustment must then be made for the potentially biasing effect of comorbidity; in ABDS 2015, the bias adjustment has been effected through altering the suite of disability weights.
The final step is to calculate YLD for each disease, which is calculated as the point prevalence multiplied by the disability weight summed over all sequela levels (for each age and sex).
Estimating the total burden (DALY)
As they use time as a common currency, the YLL and YLD can be summed to measure DALY: 1 DALY represents the loss of 1 year of healthy life. So, DALY = YLL + YLD.
Further technical details on the computation of YLL, YLD and DALY can be found in the AIHW report Australian Burden of Disease Study 2015: methods and supplementary material.
Estimating health-adjusted life expectancy (HALE)
Using Sullivan’s method, HALE is derived by computing the total years lived without disability using a measure of the years lived at each age group (obtained from ABS life tables for 2010-2012 and 2014-2016 ) and a measure of the years lived with disability for 2011 and 2015 (obtained from ABDS 2015). Technical details for the computation of HALE can be found in the relevant HealthStats methods paper.