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Estimating the Aboriginal and Torres Strait Islander Resident Population

Each Population Census gives an opportunity to update ABS estimates of the Aboriginal and Torres Strait Islander population, both at a broad national level and for regions of Australia. This process involves not just the Census counts but also estimates from the Census Post Enumeration Survey (PES) of the number of persons that have been missed by the Census.

The population estimates are obtained by smoothing PES-based net undercount estimates with high standard errors towards a stable predicted value. This process has been extensively discussed with stakeholders, including at two meetings of the Aboriginal and Torres Strait Islander Demographic Statistics Expert Advisory Group; it was also considered by the Methodology Advisory Committee in November 2011. The Bayesian model underlying the smoothing has been developed as a result of these consultations.

The estimation proceeded as follows. A prediction of the proportion of persons missed in the 2011 Census was obtained for a set of 18 regions, based on a logistic regression model applied to items that are available on the Census. The Bayesian modelling approach was then applied to smooth the estimates from PES towards these predictions plus a common "intercept" value. This intercept was allowed to be somewhat different for the four approximate regions classified as in Northern Australia, to reflect the particular challenges of collecting data in these regions.

The amount of smoothing used was chosen to give good model fit, an approach known as "Empirical Bayes". Consideration was also given to smoothing over time, but this was not implemented as there appeared to be important changes in Indigenous identification between the 2006 and 2011 Censuses. The results of the smoothing and the preliminary population estimates for 30 June 2011 will be published in late September 2012 in Australian Demographic Statistics, March Quarter 2012 (cat. no. 3101.0). Final population estimates will be released in August 2013.

Further Information
For more information, please contact Philip Bell (08 8237 7304, philip.bell@abs.gov.au)