Notes on the data: ABORIGINAL AND TORRES STRAIT ISLANDER CHRONIC DISEASES AND CONDITIONS
Estimated Aboriginal population with circulatory system diseases, 2018–19
Policy context: The heart, blood and blood vessels make up the circulatory system. The leading conditions contributing to circulatory system disease burden and mortality are hypertension (high blood pressure), stroke, and ischaemic heart disease (coronary heart disease). These diseases are mainly caused by a damaged blood supply to the heart, brain and/or limbs, and share a number of risk factors. Behavioural risk factors, such as poor diet and tobacco smoking, contribute significantly to the likelihood of developing a circulatory system disease.
In 2018–19, 15.3% of Aboriginal people in Australia reported having at least one heart or other circulatory system condition.
- PHIDU (www.phidu.torrens.edu.au), based on direct estimates from the 2018–19 National Aboriginal and Torres Strait Islander Health Survey, ABS TableBuilder.
Modelled Estimates: Overview
National surveys like the 2018–19 National Aboriginal and Torres Strait Islander Health Survey (NATSIHS) are designed to measure population characteristics for Australia or for a large proportion of the Australian population such as for a state or territory. Due to sample size limitations, it is not possible to provide accurate measures of population characteristics at lower geographic levels. The survey sample size is often too small, resulting in high margins of error. To meet user demands for information at lower geographic levels, the Australian Bureau of Statistics (ABS) can produce modelled estimates. Modelled estimates use both the survey responses for NATSIHS, together with other information about the population of a geographic area gained from the Population Census and administrative data sources to build a predictive model that estimates a given characteristic for a small area. The term “small area” refers to a geographical area that is smaller than a state or territory, such as Indigenous Areas, Indigenous Regions and Primary Health Networks. Strictly speaking modelled estimates are not as reliable as directly estimated survey measures from the NATSIHS. Measures of error are provided with these estimates (in the data) and the Technical Appendix explains what types of error are present.
Modelled estimates can be used for observing national trends by using the complete set of modelled data for IAREs across Australia or a state/territory to support program evaluation or resource allocation or looking at trends across a range of IAREs. For example, looking at a range of areas in remote Australia or along the Eastern seaboard with high or low number or proportion of people with the selected characteristic. A modelled estimate for a single area on its own should be used with extreme caution. Models are limited by the input data. Often significant local information about particular small areas exists but has not been collected for all areas and cannot be incorporated into the models.
The ABS has used a number of methods to measure the quality of the estimates, one of which is the relative root mean squared error (RRMSE) of the modelled estimates. The RRMSEs are included with the data. Users are advised that:
- estimates with RRMSEs less than 25% are considered reliable for most purposes;
- estimates with RRMSEs from 0.25 and to 0.50 have been marked (~) to indicate that they should be used with caution; and
- those greater than 0.50 but less than 1 are marked (~~) to indicate that the estimate is considered too unreliable for general use.
Modelled Estimates: Indigenous Areas and Indigenous Regions
Small area modelled estimates are produced by the ABS to provide users reliable estimates at a lower geographic level than State or Territory. Initially, the ABS produced a set of estimates from the 2018–19 NATSIHS for Indigenous Regions. PHIDU raised the possibility of having similar estimates for a selection of the variables at the (smaller) Indigenous Area level, for Indigenous Areas where the population was large enough and the particular variable had a sufficiently high proportion in the population. The ABS agreed, and it is the result of their further work that is presented here.
Where estimates could not be made for an Indigenous Area, as a result of its population size, the data for that Indigenous Area have been grouped with other, unpublished Indigenous Areas within the over-arching Indigenous Region, and a rate for the combined group calculated and published. Modelled estimates use both the survey responses from the NATSIHS, together with other information about the population of a geographic area gained from the Population Census and administrative data sources to build a predictive model that estimates a given characteristic for a small area. Details of the method used and accuracy of results are available from the ABS Explanatory Notes: Modelled estimates for small areas based on the 2018–19 National Aboriginal and Torres Strait Islander Health Survey
For the Indigenous Regions of Tasmania (IREG601) and Australian Capital Territory (IREG801), direct estimates were published instead of modelled estimates. Estimates for States and Territories, Greater Capital City Statistical Areas (GCCSA) and Remoteness Areas are also direct estimates, extracted using the ABS TableBuilder.
As part of the National Aboriginal and Torres Strait Islander Health Survey (NATSIHS), respondents were asked if they had ever been told by a doctor or nurse that they had one or more heart or other circulatory system conditions and if they considered they currently have one or more such conditions.
The following conditions, however, were included regardless of whether the condition was current and/or long-term:
- heart attack
- other ischaemic heart diseases
- other cerebrovascular diseases
A long-term condition is defined as a condition that has lasted, or is expected to last, for 6 months or more.
Geography: Data available by Indigenous Area (including Indigenous Region) and Remoteness Area
Numerator: Estimated number of Aboriginal people with circulatory system diseases
Denominator: Total Aboriginal population
Detail of analysis: Indirectly age-standardised rate per 100 population; and/or indirectly age-standardised ratio, based on the Australian standard
Indigenous Areas: Age-standardised rates are based on Australian Bureau of Statistics data, produced for PHIDU, from the 2018–19 National Aboriginal and Torres Strait Islander Health Survey.
Indigenous Regions: Age-standardised rates are based on Australian Bureau of Statistics data from the 2018–19 National Aboriginal and Torres Strait Islander Health Survey: Small Area Estimates, Australia (ABS Cat. no. 4715.0).
Remoteness Areas: Age-standardised rates (direct estimates) are calculated from Australian Bureau of Statistics customised reports, produced for PHIDU, from the 2018–19 National Aboriginal and Torres Strait Islander Health Survey.