The Australian Bureau of Statistics (ABS) uses a cohort-component method for producing population projections. Using this method, assumptions made about future levels of fertility, mortality, and migration are applied to a base population (split by sex and single year of age) to obtain a projected population for the following year. The assumptions are then applied to this new (projected) population to obtain a projected population for the next year. This process is repeated until the end of the projection period is reached.
A similar method can also be used to produce population estimates for previous years (in this release, years prior to the 2011 Census of Population and Housing). This technique requires assumptions to be made about past levels of mortality taking into account the most recent Census data to utilise the best quality estimates available. These are applied to the base population to obtain a 'reverse-survived' population for the previous year. The assumptions are then applied to this new (reverse-survived) population to obtain a population for the preceding year. This process is repeated until the first year of the estimation period is reached.
Estimates and projections presented in this release supersede estimates and projections based on earlier censuses. The assumptions used differ from those in previous publications. As a result, and in addition to the use of a different base population, which is significantly larger than the previous base population, the size, structure and components of the estimated and projected Aboriginal and Torres Strait Islander population are different to those previously published for the same period.
Span of estimates and projections
Backcast estimates of the Aboriginal and Torres Strait Islander population in this release span the period 30 June 2001 to 30 June 2011 and are available for Australia and the states and territories. Estimates for the period 30 June 1996 to 30 June 2000 have also been produced and are available as an illustrative series in Appendix 1. Given the 15-year interval for which the assumption of improving life expectancy at birth is applied, backcast data should be interpreted with caution.
Projections of the Aboriginal and Torres Strait Islander population in this release span the period 30 June 2012 to 30 June 2026 and are available for Australia, states and territories, Indigenous Regions and Remoteness Areas. Again, given the 15-year interval for which the assumptions are applied, projections data should be interpreted with caution.
The base population is the Aboriginal and Torres Strait Islander estimated resident population of Australia at 30 June 2011, derived from 2011 Census of Population and Housing counts of Aboriginal and Torres Strait Islander Australians, adjusted for net undercount as measured by the Post Enumeration Survey (PES). The base population estimates for the Northern Territory at 30 June 2011 are based on age-heaping adjusted data. For further information on this adjustment and the base population, see Estimates of Aboriginal and Torres Strait Islander Australians (cat. no. 3238.0.55.001).