Methods
Age-standardisation is a method of removing the influence of age when comparing populations with different age structures – either different populations at one time or the same population at different times.
Direct age-standardisation was used in this report. The Australian estimated resident population as at 30 June 2001 has been used as the standard population.
The observed value of a rate may vary because of the influence of chance and natural variation. To indicate if 2 rates are statistically different, 95% confidence intervals can be calculated, and statistically significant differences highlighted.
A 95% confidence interval describes a span of numbers around the estimate that has a 95% chance of including the true value. When comparing 2 groups, if the 2 confidence intervals do not overlap, the reader can be confident that the difference between the groups is real, and not due to chance.
Confidence intervals were calculated for survey data in this report.
Comparisons of regions in this report use the Australian Bureau of Statistics (ABS) Australian Statistical Geography Standard (ASGS) 2016 remoteness structure, which groups Australian regions into 6 remoteness areas.
The 6 remoteness areas are Major cities, Inner regional, Outer regional, Remote, Very remote and Migratory. These areas are defined using the Accessibility/Remoteness Index for Australia, which is a measure of the remoteness of a location from the services that large towns or cities provide.
In some instances, data for remoteness areas have been combined because of small sample sizes.
It is possible that not every record in a data set will correspond directly to a remoteness area. Where data do not correspond, they have been excluded from analyses by remoteness area.
Further information on the ASGS is available on the ABS website.
Socioeconomic classifications in this report are based on the ABS Index of Relative Socio-economic Disadvantage (IRSD). Geographic areas are assigned a score based on social and economic characteristics of that area, such as income, educational attainment, public sector housing, unemployment and jobs in low-skill occupations. The IRSD relates to the average disadvantage of all people living in a geographical area. It cannot be presumed to apply to all individuals living in the area.
For the analyses in this report, the population is divided into 5 socioeconomic areas, with roughly equal populations (each around 20% of the total), based on the level of disadvantage of the statistical local area of their usual residence. The first group includes the 20% of areas with the highest levels of relative disadvantage (referred to as Group 1, lowest or most disadvantaged), while the last group includes the 20% of areas with the lowest levels of relative disadvantage (referred to as Group 5, highest or least disadvantaged).
It is possible that not every record in a dataset will correspond directly to one of these socioeconomic areas. Where data do not correspond, they have been excluded from analyses by socioeconomic area.
The IRSD values used in this report are based on the ABS 2016 Census of Population and Housing with the exception of the National Mortality Database. Further information is available on the ABS website.
In this report, comparisons are made between Aboriginal and Torres Strait Islander people and people who do not identify as Indigenous.
People with ‘not-stated’ Indigenous status are excluded from any analysis by Indigenous status, unless otherwise stated. In cases where people with ‘not-stated’ Indigenous status are included, the comparison is between Indigenous Australians and ‘other Australians’.
National populations
Population data are used throughout this report to calculate rates. The population data used are estimated resident populations (ERPs) derived from the ABS Census of Population and Housing.
The COVID-19 pandemic and the resulting Australian Government closure of the international border from 20 March 2020, caused significant disruptions to the usual Australian population trends. This report uses Australian Estimated Resident Population (ERP) estimates that reflect these disruptions.
In the year July 2020 to June 2021, the overall population growth was much smaller than the years prior – in particular there was a relatively large decline in the population of Victoria. ABS reporting indicates these were primarily due to net-negative international migration.
This may complicate interpretation of statistics calculated from these ERPs. For example, rates and proportions may be greater than in previous years due to decreases in the denominator (population size) of some sub-populations.
For more information: National, state and territory population, June 2021.
Throughout this report, rates of deaths and hospitalisations are age-standardised. In these cases, the standard population used to calculate the age-standardised rate is the Australian ERP as at 30 June 2001.
Aboriginal and Torres Strait Islander populations
The ABS 2016 Census base series B Indigenous population projections were used to derive rates (ABS 2019). To calculate non-Indigenous estimates, the Indigenous projections were subtracted from the total Australian estimated resident population data.
References
ABS (Australian Bureau of Statistics) (2019) Estimates and projections, Aboriginal and Torres Strait Islander Australians, ABS, Australian Government, accessed 1 December 2021.