### What is burden of disease?

Burden of disease analysis measures the impact of disease and injury in a population by estimating the years of life lost (YLL, fatal burden) and years lived with disability (YLD, non-fatal burden). The sum of non-fatal and fatal burden equates to the total burden (disability-adjusted life year, DALY).

1 DALY is equivalent to 1 year of healthy life lost.

Burden of disease studies allow the impact of both deaths and living with illness to be compared and reported in a consistent manner. The health impacts and distribution of diseases and injuries contribute to the evidence base to inform health policy and programs, and service delivery.

### How are burden of disease estimates (DALY, YLD, YLL) calculated?

Disability-adjusted life years (DALY) are estimated by combining the years of life lost (YLL) with the years lived with disability (YLD) in a single reference year for each sex, age group and disease or injury.

DALY = YLL + YLD

YLL equals the sum of the number of deaths due to the disease at each age multiplied by the number of remaining years that a person would on average expected to have lived according to an aspirational life expectancy.

YLD is estimated by multiplying the point prevalence of all sequelae (that is, consequences of a disease) by a disability weight which reflects the severity of the health state. A health state reflects a combination of signs and symptoms that result in health loss (for example, end stage of chronic liver disease). The disability weights used in ABDS 2023 were sourced from the Global Burden of Disease Study 2013 (GBD 2013 Collaborators 2015). Point prevalence is defined as the number of people with a condition at a particular point in time, for a reference year.

For 2023, burden estimates were mostly based on trends from previous ABDS reference years, 2020 and 2021 data where available and appropriate. Further detail about the trend analyses can be found in the Technical notes.

### How is health-adjusted life expectancy calculated?

Health-adjusted life expectancy (HALE) extends the concept of life expectancy by considering the time spent living with ill health from disease and injury. HALE is measured using the morbidity and mortality experienced by the population for a particular reference year.

In the ABDS, Sullivan’s method was used to calculate HALE (see Jagger et al. 2014). Further information can be found in the Australian Burden of Disease Study 2018: methods and supplementary material report.

For ABDS 2023, the life table for 2023 derived from the ABS provisional deaths and projected 2023 YLD rates were used to calculate HALE. For more information see HALE in the Technical notes.

### Which diseases are included in the Australian Burden of Disease Study?

Burden of disease analysis provides estimates for an extensive list of diseases and injuries, and the list of diseases has been devised to be mutually exclusive (non-overlapping).

The ABDS 2023 disease list comprises 220 specific diseases or conditions (such as coronary heart disease, stroke, lung cancer or bowel cancer), grouped into 17 disease groups of related diseases or conditions (such as cardiovascular diseases or cancer). Estimates for injuries are calculated from two perspectives – external cause of injury (such as road traffic accident) and nature of injury (such as traumatic brain injury).

Conditions that could not be individually specified are included in a residual category for each disease group (such as ‘other cardiovascular conditions’).

COVID‑19 is a disease under the Infectious diseases group in the ABDS 2023. Further information on the data and methods used for COVID‑19 is provided in the Technical notes.

More information on the diseases included in the Australian Burden of Disease studies can be found in the Australian Burden of Disease Study: methods and supplementary material 2018 report.

### How does the Australian Burden of Disease Study 2023 differ from previous studies?

To provide burden of disease estimates best matched to the public health context for the Australian population, previous Australian Burden of Disease Studies started when the key data resources became available for most included diseases. The complexity of the process (including reviewing and improving disease-specific methods and resources, data extraction, analysis and checking) results in a 3–year to 4–year delay between the reference period and release of results.

To address challenges such as timeliness and completeness of available data, the burden estimates for the ABDS 2023 were largely based on trend analyses rather than gathering data for each reference period, as was done in previous studies.

Trend analysis is a method used to evaluate the pattern of burden estimates over time and to predict burden estimates for the period of interest. Trend analysis allows for burden to be estimated for the current year (2023), based on the assumption that past trends have continued. The COVID‑19 pandemic may have influenced morbidity and mortality of some diseases. However, for most diseases adjustments due to COVID‑19 impacts were not in scope for ABDS 2023 due to limited data availability at the time of analysis.

Estimates from the trend analysis should be interpreted with caution, as the changes in burden due to factors outside disease epidemiology, such as new public health interventions, were not accounted for in this analysis. The early impact of COVID‑19 restrictions on Australia’s population was accounted for in the population data used for 2023.

This Study includes estimates for COVID‑19. Burden from COVID‑19 and lower respiratory infections (including influenza and pneumonia) were estimated from 2023 data available at the time of analysis (further detail is provided in the Technical notes). However, these estimates may be revised in the future, as more data become available for the latter half of 2023.

The ABDS 2023 does not include subnational or risk factor estimates. The most recent estimates are presented in the Australian Burden of Disease Study: impact and causes of illness and death in Australia 2018 report.

Further information on the data and methods used in ABDS 2023 can be found in the Technical notes

### Which data sources are used in the Australian Burden of Disease Study 2023?

Mortality data to calculate YLL estimates for 2023 were sourced from the AIHW National Mortality Database (NMD) (deaths occurring from 2011 to 2021 were used in trend analysis) and the ABS provisional death registration data for January to June in 2023 (used to validate projected deaths for 2023 and make adjustments where required).

Deaths due to COVID‑19 and lower respiratory infections (including influenza and pneumonia) were mainly sourced from the ABS provisional deaths for available months in 2023, with deaths for the remainder of 2023 modelled based on monthly trends (see Technical notes for further detail).

The YLL estimates for 2023 should be interpreted with caution. Some cause of death information used in the analyses is subject to change pending the status of coroner investigation. The ABS revisions process is described in detail elsewhere (ABS 2021). The YLL estimates presented may be revised for the next Study when more information becomes available for 2023.

For YLD estimates, there is no single comprehensive and reliable source of data for the incidence, prevalence, severity and duration of all non-fatal health conditions. Morbidity estimates were drawn from a wide variety of data sources, and generally based on the best single source. This included administrative data, national surveys, disease registers and epidemiological studies. Potential sources for disease-specific morbidity data were required to:

• have case definitions appropriate to the disease being analysed
• be relevant to the Australian population
• be timely, accurate, reliable and credible.

YLD estimates for 2023 were calculated using trend analysis based on data for previous ABDS reference years (2003, 2011, 2015, 2018, 2019 (calculated as part of ABDS 2022) and updated prevalence data for 2020 where available (for example, hospitalisation and cancer incidence data and data from the National Survey of Mental Health and Wellbeing) and appropriate (for example, for diseases that were not largely impacted by COVID‑19 and the pandemic restrictions and pause on non-essential surgeries etc.).

Further information on the data and methods used in ABDS 2023, as well as differences between the ABDS 2023 and the ABDS 2018, can be found in the Technical notes. The overarching methods used for previous ABDS, and more information on the redistribution of deaths, can be found in the Australian Burden of Disease Study: methods and supplementary material 2018 report.

### Why use estimates from the Australian Burden of Disease Study 2023 instead of the Australian Burden of Disease Study 2018?

The ABDS 2023 was undertaken to build on the AIHW’s previous burden of disease studies and current disease monitoring work. The ABDS 2023 provides an update of burden of disease estimates using the infrastructure developed as part of ABDS 2011, 2015 and 2018.

The ABDS 2023 provides national burden of disease estimates relevant to the public health context for the Australian population for 2023. It includes burden estimates for the year of release (2023) and burden estimates for COVID‑19.

Due to different methods used in the ABDS 2023 compared to previous studies, estimates from the ABDS 2023 are not directly comparable, and may differ from, published estimates in previous Australian burden of disease studies.

For further information on the differences between ABDS 2023 and previous studies see How does the Australian Burden of Disease Study 2023 differ from previous studies?

### Why use estimates from the Australian Burden of Disease Study 2023 instead of the Australian Burden of Disease Study 2022?

The ABDS 2023 builds on work from the ABDS 2022, which was the first ABDS to estimate burden for the year of release based on historical trends and to include burden due to COVID‑19. Since the ABDS 2022, methods for estimating burden due to COVID‑19 have been refined and some estimates from previous years were revised due to updates in key data sources, such as the National Survey of Mental Health and Wellbeing 2020–21. Therefore, estimates from the ABDS 2023 are not directly comparable, and may differ from, published estimates in previous Australian burden of disease studies. However, estimates for different reference years within the ABDS 2023 are comparable.

For further information on the differences between ABDS 2023 and previous studies see ‘How does the Australian Burden of Disease Study 2023 differ from previous studies?’

### Where do I find subnational estimates, such as by state/territory?

The ABDS 2023 includes national estimates only. For subnational (state/territory, remoteness area, socio-economic group) estimates, see the Australian Burden of Disease Study: impact and causes of illness and death in Australia 2018 report. Subnational estimates may not add up to the national estimates. Updated subnational estimates are expected to be included in the next major update of the Australian Burden of Disease Study in late 2026.

### Are risk factors included in the Australian Burden of Disease Study 2023?

The ABDS 2023 does not include risk factors. For the most recent estimates, see the Australian Burden of Disease Study: impact and causes of illness and death in Australian 2018 report.

### How does Australia compare to other countries?

International comparisons are important and can provide a useful perspective of global disease burden. The Global Burden of Disease (GBD) studies and the WHO’s Global Health Estimates help to inform comparisons that show how health challenges differ globally and regionally. Comparisons are best made with data that are based on consistent definitions and that have similar collection methods and population coverage. In practice, this means that results are comparable within a study but not between studies. Hence, the GBD and WHO results for Australia cannot be compared with results produced in this study.

Australian estimates can be compared with those for countries and regions as estimated in the GBD 2019. For this comparison, see Australian Burden of Disease Study: impact and causes of illness and death in Australia 2018 report.

### Why do some diseases have no fatal or non-fatal estimates?

Some diseases do not have YLL or YLD estimates as either mortality does not occur from that disease (such as hearing loss disorders), or the disease is only fatal and as such there is no morbidity (such as sudden infant death syndrome). For some rare infections, there were no deaths or morbidity associated with the disease in certain reference years.

### What population data were used?

All Australian population-based rates for 2021, 2020, 2019, 2018 were calculated using populations rebased to the 2016 Census (accessed 15 December 2022) (ABS 2022).

Population-based rates for 2015 were calculated using final population estimates from the 2011 Census (accessed 22 December 2018) (ABS 2018).

Population-based rates for 2011 and 2003 were calculated using final population estimates from the 2011 Census (ABS 2017).

Population data for 2023 were sourced from population projections by the Centre for Population (2022). This was the only available source that accounted for the early impacts of the COVID–19 pandemic on Australia’s population. The population under the ‘central scenario’ was used for this Study, which assumed overseas migration to Australia was significantly affected by the COVID–19 pandemic.

The 2001 Australian Standard Population was used for all age-standardisation, as per AIHW and ABS standards (ABS 2016).

### What information is available about the quality of estimates in the Australian Burden of Disease Study 2023?

The ABDS 2023 estimates were produced using the best data available in the scope and time frame of the Study.

Disease burden estimates for 2023 were largely based on projecting historical trends. Uncertainty assessments were also conducted alongside trend analysis. To provide information on the quality of input estimates from previous reference years (2003, 2011, 2015 and 2018), a quality index was developed to rate estimates according to the relevance and quality of source data, and methods used to transform data into a form required for this analysis. Generally, the higher the rating, the more relevant and accurate the estimate. For disease burden due to COVID‑19 and lower respiratory infections (including influenza and pneumonia), this approach to rating data quality was used to reflect uncertainty.

To report on the reliability of projected burden of disease measures, the inclusion of confidence intervals associated with regression estimates was explored. However, these were not presented as these relate to the regression models and do not reflect the underlying uncertainty associated with data inputs that inform prevalence estimates. Other outputs of the regression models may indicate the best fit projection based on the set of YLL and YLD crude rates available for each age-sex-cause group. However, these do not necessarily represent the most appropriate projections in the context of the overall epidemiology of a given disease or injury, especially when considering impacts of the COVID‑19 pandemic.

Fatal burden (YLL) estimates were considered to have the highest rating for both data and methods used, whilst non-fatal burden (YLD) estimates varied depending on the disease or injury and the data sources used.

The quality of input estimates in the ABDS 2023 for earlier reference years (2003, 2011, 2015 and 2018) are the same as the quality presented in the ABDS 2018. Therefore, refer to Appendix B in the Australian Burden of Disease Study: impact and causes of illness and death in Australia 2018 report (AIHW 2021a) and the Australian Burden of Disease Study: methods and supplementary material 2018 report (AIHW 2021b) for more detail on the quality of the YLD estimates and the data and methods used for the earlier reference years. The quality statements for COVID‑19 and lower respiratory infections (including influenza and pneumonia) for 2023 are presented in the Technical notes.

### Where can I get more information on methods used in Australian Burden of Disease Study 2023?

Information about the methods used for 2023 burden of disease estimates are presented in the Technical notes. Aside from COVID‑19 and lower respiratory infections (including influenza and pneumonia), the methods used for the earlier reference years to inform the trend for 2023 are the same as methods used in the ABDS 2018. For information about methods used for specific diseases for earlier reference years (2003, 2011, 2015 and 2018), refer to the Australian Burden of Disease Study: methods and supplementary material 2018 report.