Notes on the data: Health risk factors

Estimated male, female or total population, aged 2 to 17 years, who were obese or overweight, 2017-18

Policy context: Overweight and obesity in childhood and adolescence can cause a range of physical and emotional health problems; and obesity increases the risk of chronic disease and premature death in adulthood. In 2017-18, around one in four (24.9%) children and young people aged 2-17 years were overweight or obese, comprised of 16.7% overweight and 8.2% obese. There has been no change since 2014-15 (25.8%) in the proportion of children and young people who were overweight or obese [1,2,3].

Reference

Australian Bureau of Statistics (ABS). Children’s Risk Factors, National Health Survey: First Results, 2014-15. Available from: http://www.abs.gov.au/ausstats/abs@.nsf/mf/4364.0.55.001; last accessed 4 December 2016
Australian Bureau of Statistics (ABS). Table 16: Children's Body Mass Index, waist circumference, height and weight. National Health Survey: First Results, 2014-15. Canberra: ABS; 2015. Available from: https://www.abs.gov.au/AUSSTATS/abs@.nsf/DetailsPage/4364.0.55.0012014-15?OpenDocument; last accessed 4 December 2016
Australian Bureau of Statistics (ABS). Table 16: Children's Body Mass Index, waist circumference, height and weight. National Health Survey: First Results, 2017-18. Canberra: ABS; 2018. Available from: https://www.abs.gov.au/AUSSTATS/abs@.nsf/DetailsPage/4364.0.55.0012017-18?OpenDocument; last accessed 13 December 2019

Notes:

Differences from data published by the Australian Bureau of Statistics (ABS):

Data by quintile of socioeconomic disadvantage and Remoteness will differ to the extent that data extracted from Survey TableBuilder have been randomised, whereas those published by the ABS are not. In addition, rates published by the ABS for modelled estimates are generally crude rates; rates published by PHIDU are age-standardised.

In the absence of data from administrative data sets, estimates are provided at the Population Health Area (PHA) level for selected health risk factors from the 2017–18 National Health Survey (NHS), conducted by the Australian Bureau of Statistics (ABS). The estimates at the Population Health Area (PHA) are modelled estimates produced by the ABS (estimates at the Local Government Area (LGA) and Primary Health Network (PHN) level were derived from the PHA estimates).

Details of the method used and accuracy of results are available from the ABS paper Explanatory Notes: Modelled estimates for small areas based on the 2017-18 National Health Survey, available here.

For the Primary Health Network (PHN) data, differences between the PHN totals and the sum of LGAs within PHNs result from the use of different geographic correspondence files.

Estimates for quintile of socioeconomic disadvantage of area and Remoteness Area are direct estimates, extracted using the ABS Survey TableBuilder.

Users of these modelled estimates should note that they do not represent data collected in administrative or other data sets. As such, they should be used with caution, and treated as indicative of the likely social dimensions present in an area with these demographic and socioeconomic characteristics.

The numbers are estimates for an area, not measured events as are, for example, death statistics. As such, they should be viewed as a tool that, when used in conjunction with local area knowledge and taking into consideration the prediction reliability, can provide useful information that can assist with decision making for small geographic regions. Of particular note is that the true value of the published estimates is also likely to vary within a range of values as shown by the upper and lower limits published in the data (xlsx) and viewable in the column chart in the single map atlases.

What the modelled estimates do achieve, however, is to summarise the various demographic, socioeconomic and administrative information available for an area in a way that indicates the expected level of each health indicator for an area with those characteristics. In the absence of accurate, localised information about the health indicator, such predictions can usefully contribute to policy and program development, service planning and other decision-making processes that require an indication of the geographic distribution of the health indicator.

The relatively high survey response rate in the NHS provides a high level of coverage across the population; however, the response rate among some groups is lower than among other groups, e.g., those living in the most disadvantaged areas have a lower response rate than those living in less disadvantaged areas. Although the sample includes the majority of people living in households in private dwellings, it excludes those living in the very remote areas of Australia and discrete Aboriginal and Torres Strait Islander communities; whereas these areas comprise less than 3% of the total population, Aboriginal people comprise up to one third of the population. The survey does not include persons usually resident in non-private dwellings (hospitals, gaols, nursing homes - and also excludes members of the armed forces).

This and other limitations of the method mean that estimates have not been published for PHAs with populations under 1,000.

The ABS 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.

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 NHS interview, were used to calculate the BMI. For more information about BMI classifications produced for children, refer to the Body Mass Index definition in the National Health Survey: First Results, 2017-18 Glossary.

Note that the modelled estimates are based on the 56.1% of children and young people aged 2 to 17 years 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 Appendix 2: Physical measurements in the ABS publication National Health Survey: First Results, 2017-18 (Cat. no. 4364.0.55.001).

Geography: Data available by Population Health Area, Local Government Area, Primary Health Network, quintile of socioeconomic disadvantage of area and Remoteness Area

Numerator: Estimated number of males, females or persons aged 2 to 17 years who were assessed as being overweight (not obese) or obese, based on their measured height and weight

Denominator: Male, female or total population aged 2 to 17 years

Detail of analysis: Indirectly age-standardised rate per 100 males, females or persons (aged 2 to 17 years); and/or indirectly age-standardised ratio, based on the Australian standard

PHA, LGA & PHN: Age-standardised rates are based on Australian Bureau of Statistics data, produced as a consultancy for PHIDU, from the 2017—18 National Health Survey.

Quintiles & Remoteness: Compiled by PHIDU based on direct estimates from the 2017–18 National Health Survey, ABS Survey TableBuilder.