A. Method
The cohort-component method was used for these projections. In this method, the base population is projected forward annually by calculating the effect of births, deaths and migration within each age-sex group according to the specified fertility, mortality and migration assumptions.
These projections were produced in two stages. Firstly, the resident population of each capital city and balance of State/Territory was projected by single year of age and sex. Secondly, the population of each SLA within each capital city and balance of State/Territory was projected by single year of age and sex, and constrained to sum to the respective capital city and balance of State/Territory projected population for each year.
B. Assumptions for Capital City and Balance of State/Territory Projections
The base population for the capital city and balance of State/Territory projections was the preliminary estimated resident population in each area, at 30 June 1999. The assumptions for fertility, mortality, overseas migration and interstate migration are the same at the capital city and balance of State/Territory level as Series II outlined in Population Projections, Australia 1999 to 2101 (Cat. No. 3222.0) published on 17 August 2000. Series II incorporates assumptions for Australia of 'low' fertility (a total fertility rate of 1.60 births per women from 2008), 'medium' overseas migration (an annual net overseas migration gain of 90,000) and 'medium' interstate migration.
C. Assumptions for SLA Projections
The base population for SLAs in NSW, Victoria, South Australia, Western Australia, Tasmania and ACT was the preliminary estimated resident population in each area by single year of age and sex, at 30 June 1999. For SLAs in Queensland and Northern Territory, the revised estimated resident population in each area at 30 June 1999 was used as the base.
The fertility assumptions were based on average age-specific fertility rates observed in each SLA between 1991 and 1997, projected to change in line with the State/Territory assumptions outlined in Population Projections, 1997 to 2051 (Cat. No. 3222.0) published on 14 July 1998. The mortality assumptions were based on the State/Territory age-and-sex-specific mortality rates. Assumptions for 1998-2006 were calculated using the rates of mortality decline observed in each State/Territory between 1987-91 and 1992-96. Assumptions beyond 2006 were calculated using the rates of mortality decline observed in Australia during 1967-71 to 1992-96. The mortality assumption was then adjusted to reflect the recent mortality experienced in each SLA.
In constraining the SLA population projections to the projections published in Population Projections, Australia 1999 to 2101, the fertility and mortality assumptions used in the latter projections will in effect filter down to the SLA projections.
The assumed migration levels were based on historical trends of net migration in each SLA, the assumed levels of State/Territory overseas and interstate migration, and any recent State/Territory government dwelling and population projections or local land planning information. The assumed SLA net migration levels were constrained to the capital city and balance of State/Territory assumptions in Series II. The age-sex distributions for the assumed migration levels were based on overseas and inter-SLA migration rates used in the calculation of published ABS SLA age-sex population estimates, which were originally derived from 1996 Census of Population and Housing migration data.
D. Nature of Projections
The nature of the projection method and inherent fluctuations in population dynamics mean that care should be taken when using and interpreting the projection results. The projections are not exact forecasts but simply illustrate future changes which would occur if the stated assumptions were to apply over the projection period. While the projections take account of land planning and other decisions by governments known at the time the projections were derived, the ABS does not always have access to the policies or decisions of Commonwealth, State and Local Governments and businesses that assist in accurately forecasting small area populations. The projections do not attempt to allow for non-demographic factors (eg. major government policy decisions, economic factors, catastrophes, wars) which may affect future demographic behaviour.
The unpredictability of migration trends, especially in the short-term, can have a significant effect on projection results. Special care should be taken with small SLAs (populations under 1,000 people) and small age-sex cells (populations under 100 people). Accordingly, SLAs with a base population of less than 1,000 have generally been kept constant as the age-sex cells are too small for reliable projection.
All SLAs in these projections are based on the Australian Standard Geographic Classification boundaries as they existed at the 1996 Census (ASGC 1996). The actual boundaries for a given SLA, or for other geographic regions such as Local Government Areas (LGAs) derived from this SLA, may change over time making the projections no longer comparable with other data.
E. Liability
It is important to recognise that the projection results given in this report simply reflect the assumptions made about future fertility, mortality and migration trends. While the assumptions are formulated on the basis of an objective assessment of demographic trends over the past decade and their likely future dynamics, there can be no certainty that they will be realised.
While ABS takes responsibility for the method employed, the assumptions used are the final responsibility of the client, and the projections are not official ABS population statistics.
No liability will be accepted by the Australian Bureau of Statistics for any damages arising from decisions or actions based upon these population projections.
F. Referencing these statistics
These projections should be referred to as projections prepared by the ABS according to assumptions agreed to by the Commonwealth Department of Health and Aged Care. The short reference is - Commonwealth Department of Health and Aged Care projections.
G. Additional Information
For further information on population projections refer to the ABS publication Population Projections, Australia 1999 to 2101 (Cat. No. 3222.0) available from ABS offices in all capital cities. For more information, or quotes on the preparation of alternative projections, please contact:
Matthew Berger
Demography Section
Australian Bureau of Statistics
Tel. 02 6252 6639
Email: matthew.berger@abs.gov.au
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