Notes on the data: ABORIGINAL AND TORRES STRAIT ISLANDER HEALTH RISK FACTORS

Estimated Aboriginal population, aged 15 years and over, who were underweight or in a normal weight range, overweight or obese, 2018–19

Policy context: Each increment in a person's body weight above their optimal level is associated with an increase in the risk of ill health. Overweight arises through an energy imbalance over a sustained period of time. While many factors may influence a person's weight, weight gain is essentially due to the energy intake from the diet being greater than the energy expended through physical activity. The energy imbalance need only be minor for weight gain to occur, and some people, due to genetic and biological factors, may be more likely to gain weight than others. Overweight is associated with higher mortality and morbidity, and those who are already overweight have a higher risk of becoming obese.

Being obese has significant health, social and economic impacts, is more prevalent among disadvantaged populations and is closely related to lack of exercise and diet [1]. Obesity increases the risk of suffering from a range of health conditions, including coronary heart disease, type 2 diabetes, some cancers, knee and hip problems, and sleep apnoea [1].

In 2018–19, 71.2% of Aboriginal people aged 15 years and over were overweight or obese (28.5% overweight (but not obese), 42.7% obese) and 28.9% were underweight or in a normal weight range [2].

References

Australian Bureau of Statistics (ABS). Measures of Australia’s progress, 2010. (ABS Cat. no. 1370.0). Canberra: ABS; 2010.
PHIDU (www.phidu.torrens.edu.au), based on direct estimates from the 2018–19 National Aboriginal and Torres Strait Islander Health Survey, ABS TableBuilder.

Notes:

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.

Indicator detail

The Body Mass Index (BMI) (or Quetelet's index) is a measure of relative weight based on an individual's mass and height. The height (cm) and weight (kg) of respondents, as measured during the National Aboriginal Torres Strait Islander Health Survey (NATSIHS) interview, were used to calculate the BMI. The BMI categories are as follows:

Underweight (less than 18.5);
Normal range (18.5 to less than 25.0);
Overweight (25.0 to less than 30);
Obese (30 or over).

The BMI is a useful tool at a population level for measuring trends in body weight, and helping to define population groups who are at higher risk of becoming obese, and therefore developing long-term medical conditions associated with a high BMI, such as type 2 diabetes and cardiovascular disease.

Note that the modelled estimates are based on the 60.1% of Aboriginal people 15 years and over in the sample who had their height and weight measured. For respondents who did not have their height and weight measured, imputation was used to obtain height, weight and BMI scores. For more information refer to the ABS National Aboriginal and Torres Strait Islander Health Survey methodology

Geography: Data available by Indigenous Area (including Indigenous Region) and Remoteness Area

Numerator: Estimated number of Aboriginal people aged 15 years and over who were assessed (based on their measured height and weight) as being:

underweight or in the normal weight range;
overweight (not obese);
obese;
overweight or obese.

Denominator: Total Aboriginal population aged 15 years and over

Detail of analysis: Indirectly age-standardised rate per 100 population (aged 15 years and over); and/or indirectly age-standardised ratio, based on the Australian standard

Source:

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: Compiled by PHIDU based on direct estimates from the 2018–19 National Aboriginal and Torres Strait Islander Health Survey, ABS TableBuilder.