Methods: Aboriginal People
Recording of Aboriginality in administrative data collections
Assessing the health of the Aboriginal population is difficult for a range of reasons, including errors in estimating the number of Aboriginal people in administrative health data collected by health services and population data collected by the Australian Bureau of Statistics (ABS). The recording of the Aboriginality of a person using a health service in administrative data collections may be incomplete and variable. Aboriginality may be under-reported in administrative data collections because, for a particular occasion of care, staff may not ask whether a person is or is not Aboriginal or because Aboriginal people may be reluctant or choose not to identify as Aboriginal in some circumstances.
The estimated level of enumeration of Aboriginal people in hospital data (Admitted Patient Data Collection) in NSW has increased from 53% in 2001-02 to 84% in 2017-18 (See Reporting of Aboriginality in hospital data for more detail). Recording and reporting of Aboriginality is usually better for rural and remote regions than for major cities.
Differences in population composition and age standardisation
In NSW, the Aboriginal population is relatively young, with a median age of 22 years, compared to the non-Aboriginal population, with a median age of 38 years (2016 Census data). Furthermore, the structures of the Aboriginal and non-Aboriginal populations are different in NSW. For example, in 2016 in NSW, 45% of Aboriginal persons were below 20 years of age, 11% were 55 to 84 years old, and 0.2% were 85 years or older. By comparison, 24% of non-Aboriginal persons were below 20 years of age, 26% were 55 to 84 years old, and 2.2% were 85 years or older (See Population by Aboriginality for more detail).
As many health conditions are age-related, age standardisation is a technique that can be used to enhance the comparability of data, such as disease rates, between Aboriginal and non-Aboriginal populations. Age standardisation adjusts for the confounding effects of compositional differences in age structure between the populations or sub-populations being compared (AIHW).
In HealthStats NSW, directly age standardised rates are calculated using 5 year age groups. Due to the low numbers of Aboriginal persons in older age groups, persons aged 85+ years are amalgamated into a single age group for both Aboriginal and non-Aboriginal populations. By contrast, amalgamation from age 100+ years is used in age standardisation for the total population of NSW. Although amalgamating older ages allows Aboriginal and non-Aboriginal populations to be meaningfully compared, it is less suitable for comparison of disease distribution within the total population because information concerning older age groups is lost.
Due to smaller Aboriginal populations in sub-state geographies, 10 year age groups are used between 4 and 65 years of age, and persons over 65 years are amalgamated into a single age group, when calculating age standardised rates for Aboriginal and non-Aboriginal populations within Local Health Districts and Primary Health Networks in HealthStats NSW. By contrast, amalgamation from age 85+ years and 5 year age groups are used when calculating age standardised rates for the total population of Local Health Districts and Primary Health Networks.
Note that comparisons of disease and injury rates between Aboriginal and non-Aboriginal populations can sometimes be limited by the low numbers of older Aboriginal persons. The differences between the age structures of Aboriginal and non-Aboriginal populations may result in situations where rate estimates of rare and chronic diseases are less reliable in the Aboriginal compared with the non-Aboriginal population.
Aboriginal population estimates used in HealthStats NSW
The estimated resident Aboriginal populations for NSW used for direct age standardisation in HealthStats NSW were produced by the ABS and are based on the 2016 Census. The Aboriginal populations from 2006 to 2016 are recast estimates and Aboriginal populations from 2017 onwards are projections using the ABS projection Series B (which reflects current demographic trends). The non-Aboriginal populations for comparison are estimated by subtracting Aboriginal population estimates from the estimated total population for NSW. No sub-state population projections or recast estimates are currently available for Aboriginal populations based on the 2016 ABS Census. As such, only a single year of data can be reported on HealthStats NSW for sub-state Aboriginal populations, such as Local Health Districts and Primary Health Networks.
References
Australian Bureau of Statistics. Census of Population and Housing - QuickStats, Community Profiles and DataPacks User Guide, Australia, 2016. Cat no 2916.0 Canberra: ABS, 2017. Available at: https://quickstats.censusdata.abs.gov.au/census_services/getproduct/census/2016/quickstat/1"
Australian Bureau of Statistics. Estimates and Projections, Aboriginal and Torres Strait Islander Australians, 2006 to 2031. Cat no 3238.0. Canberra: ABS, 2019. Available at: https://www.abs.gov.au/AUSSTATS/abs%40.nsf/Lookup/3238.0Main+Features12006%20to%202031?OpenDocument