Technical notes
Rates
Unless otherwise stated, crude rates are presented and, as such, these rates have not been adjusted to account for differences in the age structures of different populations. Differences between populations may therefore be due to differences in age structures and not necessarily to other factors. To enhance comparability across groups where the age structure of the population may affect interpretation, age-standardisation is used where possible.
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. In this report, the direct age-standardisation method was used. For age-standardised rates in this report, five-year age groups were used, with ages over 85 years combined, thus 0–4, 5–9, 10–14, . . . . . . . . . , 80–84, 85+. For more information about age-standardisation, including the formula, see here age-standardised rate.
The Australian estimated resident population (ERP) as at 30 June 2001 has been used as the standard population.
For other rate calculations, the ABS ERP data were used to calculate most of the rates presented for administrative data collections (for example, rate of deaths, hospitalisations and mortality). The ERP data were also used to calculate some of the prevalence rates based on past NHSs which reported only prevalence counts (not rates).
For example, the NHS 2001 and NHS 2004–05 reported only counts of the number of Australians estimated to be living with neurological conditions. To calculate the percentages, AIHW used the ABS ERP for the reference year as the denominator and the estimated count of Australians living with neurological conditions as the numerator.
Rates were calculated using the ERP of the reference year as at 30 June for data that had a reference period of a calendar year (1 January to 30 December) and as at 31 December for data that had a reference period of a financial year (1 July to 30 June).
For ERP data see National, state and territory population, September 2024 | Australian Bureau of Statistics.
Socioeconomic areas
Comparisons between areas that are more or less socioeconomically disadvantaged are based on the Socioeconomic Indexes for Areas (SEIFA) which uses the Index of Relative Socioeconomic Disadvantage (IRSD).
The IRSD classifies individuals according to the socioeconomic characteristics of the area in which they live. It scores each area by summarising attributes of the population, such as income, educational attainment, unemployment rate and jobs in relatively unskilled occupations. The index does not show how individuals living in the same area differ from each other in their socioeconomic group.
Refer to the ABS Socioeconomic indexes for areas (SEIFA): Technical paper 2021 for more information.
Remoteness areas
Comparisons between remoteness areas are done using the Australian Statistical Geography Standard (ASGS) Remoteness Areas structure, which is based on area of residence. Australia is divided into 5 classes of remoteness based on a measure of relative access to services. The 5 remoteness areas are Major cities, Inner regional, Outer regional, Remote and Very remote. Refer to the ABS Remoteness structure for more information.
Margin of error
The margin of error indicates the range within which the true population value is likely to fall, at a given level of confidence (commonly 95%). In other words, it quantifies how the estimation result from a sample might differ from the actual value you would have obtained if you had studied the whole population. The larger the margin of error, the less confidence one should have that the result from the sample would accurately reflect the true value in the population.