2 Following the 1992 amendments to the Acts Interpretation Act to include the Indian Ocean Territories of Christmas Island and the Cocos (Keeling) Islands as part of geographic Australia, population estimates commencing from September quarter 1993 include estimates for these two territories. To reflect this change, another category of the state and territory level has been created, known as Other Territories. Other Territories include Jervis Bay Territory, previously included with the Australian Capital Territory, as well as Christmas Island and the Cocos (Keeling) Islands, previously excluded from population estimates for Australia.

POPULATION AND COMPONENTS OF POPULATION CHANGE

3 Australia’s population estimates for the period since 1971 are compiled according to the place of usual residence of the population. An explanation of the place of usual residence conceptual basis for population estimates is given in Demographic Estimates and Projections: Concepts, Sources and Methods (cat. no. 3228.0).

Method of estimation

4 The estimated resident population is an estimate of the Australian population obtained by adding to the estimated population at the beginning of each period the components of natural increase (on a usual residence basis) and net overseas migration. For the states and territories, account is also taken of estimated interstate movements involving a change of usual residence. Estimates of the resident population are based on census counts by place of usual residence, to which are added the estimated net census undercount and Australian residents estimated to have been temporarily overseas at the time of the census. Overseas visitors in Australia are excluded from this calculation.

5 After each census (at 30 June of the census year), estimates for the preceding intercensal period are revised by incorporating an additional adjustment (intercensal discrepancy) to ensure that the total intercensal increase agrees with the difference between the estimated resident populations at the two 30 June dates in the respective census years.

FINAL 2006 REBASING

6 The Australian Bureau of Statistics (ABS) has used the new information obtained from the 2006 census to rebase the estimated resident population (ERP) of Australia and its states and territories. The 2006 Census of Population and Housing (2006 Census) is used to construct a new base population figure for 30 June 2006. Because this new population estimate uses the Census as its main data source, it is said to be 'based' on that Census and is referred to as a population base for population estimates and projection, for subsequent reference periods. For more information on final rebasing see Feature Article: 'Final rebasing and revision of Australia's population estimates, September quarter 2001 – June quarter 2006' in this release.

New method for defining Residents Temporarily Overseas

7 The ABS has improved the measure of net overseas migration by expanding the Australian residence criteria from a 12/12 months rule to a 12/16 months rule (see Information Paper: Improved Methods for estimating Net Overseas Migration (cat.no.3107.0.55.003) and Information Paper: Statistical Implications of Improved Methods for Estimating Net Overseas Migration, Australia, 2007 (cat.no.3107.0.55.005)). This had implications for the measurement of residents temporarily overseas (RTOs) due to the change in residence criteria mentioned above. A final measure of RTOs could only be obtained 21 months after Census night, when actual traveller behaviour, and each traveller's true residence status on Census night (according to the 12/16 month rule) could be observed.

Natural increase: births and deaths

8 The births and deaths data in this release are shown by state and territory of usual residence, using year/quarter of occurrence for revised and final data and year/quarter of registration for preliminary data. This may affect some comparison within relevant tables. For preliminary estimates, births and deaths by quarter of registration are used as a proxy for quarter of occurrence. For revised estimates, a factor has been applied to the number of occurrences to allow for these occurrences which are yet to be registered. For final estimates after 30 June 1991 and June 2001, year/quarter of occurrence data are used. For further details see Demography Working Paper 1998/2 – Quarterly Birth and Death Estimates (cat. no. 3114.0).

9 The timeliness and accuracy of ABS quarterly population estimates depends in part on the timeliness and accuracy of estimates of births and deaths which are based on registrations. To be able to provide timely estimates the ABS produces preliminary estimates using births and deaths by quarter of registration as a proxy for quarter of occurrence. The major difficulty in this area stems from the fact that while the vast majority of births and deaths are registered promptly, a small proportion of registrations are delayed for months or even years. Lags or accumulations in births and deaths registrations can be caused by either:

• late notification of a birth or death event to a state or territory registry;
• delays arising from incomplete information supplied for a registration;
• procedural changes affecting the processing cycles in any of the state and territory registries; and
• resolution of issues that may arise within the ABS or registry processing systems.

11 Under reporting to the Australian Bureau of Statistics of birth registrations for the State of Victoria has recently been identified. Additional records from the Victorian Registry of Births, Deaths and Marriages for 2007 have now been received. As a consequence separate quarterly estimates for 2007 births, natural increase, population growth and estimated resident population in 2007 are not yet available for Victoria and Australia. These will be published in the rescheduled issue of Australian Demographic Statistics, December Quarter 2007 (cat. no. 3101.0) on 24 June 2008.

Net overseas migration

12 Conceptually, net overseas migration (NOM) is based on an international travellers' duration of stay being in or out of Australia for 12 months or more. It is the difference between the number of incoming travellers who stay in Australia for 12 months or more and are added to the population (NOM arrivals) and the number of outgoing travellers who leave Australia for 12 months or more and are subtracted from the population (NOM departures). For the method based on the 12/16 rule this 12 months does not have to be continuous and is measured over a 16 month reference period. For example, whether a traveller is in or out of the population is determined by their exact duration of stay in Australia over the subsequent 16 months after arrival or departure.

13 The ABS has developed improved methods for estimating NOM. This has been used in estimating Australia's official population since September quarter 2006. Estimates of NOM based on the previous methods and those based on the improved methods are not comparable. The key change is the introduction of a '12/16 month rule' for determining a person's residency in Australia, replacing the previous '12/12 month rule'. For further information on the new improved method see Information Paper: Improved Methods for Estimating Net Overseas Migration, 2007 (cat. no. 3107.0.55.003) and Information Paper: Statistical Implications of Improved Methods for Estimating Net Overseas Migration, Australia 2007 (cat. no. 3107.0.55.005).

Net interstate migration

14 Net interstate migration is a key determinant of the accuracy of state and territory population estimates. Data on interstate migration can not be directly estimated. Instead, post-censal estimates of interstate migration are modelled using administrative by-product data. Currently the data used by the ABS is information on interstate changes of address advised to Medicare Australia and to the Department of Defence in the case of the military. The Medicare-based model used for generating post-censal estimates of interstate migration is largely superseded when new Census information becomes available.

15 Due to the non-compulsory and non-universal nature of the available (indirect) data sources, post-censal quarterly estimates of interstate migration have long been considered the weakest measure of a component of population change. For further information on the process of estimating interstate migration and the administrative data used, see the Demography Working Paper: 2004/1 Review of Interstate Migration Method (cat. no. 3106.0.55.001) and the Information Paper: Evaluation of Administrative Data Sources for Use in Quarterly Estimation of Interstate Migration, 2006 to 2011 (cat. no. 3127.0.55.001).

Defence force adjustment

16 Medicare theoretically covers all Australian usual residents as well as those non-Australian residents granted temporary registration. However, there are a range of Australian usual residents who do not access the Medicare system, primarily due to access to alternative health services. One group is the military. As such, estimates of interstate migration produced from the interstate migration model described in the working paper Demography Working Paper: 2004/1 Review of Interstate Migration Method (cat. no. 3106.0.55.001) are adjusted to compensate for defence force movements not covered by Medicare. These adjustments are estimated using counts of defence force personnel by age, sex and state/territory, obtained from the Department of Defence, with 70% of any change in quarterly defence numbers assumed to be due to interstate migration not otherwise covered by the model.

Rates of population growth

17 These express population change over a period as a proportion (%) of the population at the beginning of the period.

Rounding

18 In this publication population estimates and their components have sometimes been rounded. Rounded figures and unrounded figures should not be assumed to be accurate to the last digit shown. Where figures have been rounded, discrepancies may occur between sums of component items and totals.

RELATED PRODUCTS

19 Other ABS products which may be of interest to users include:

Australian Demographic Statistics (cat no. 3101.0)

Australian Demographic Trends (cat. no. 3102.0)

Australian Historical Population Statistics (cat. no. 3105.0.65.001)

Births, Australia (cat. no. 3301.0)

Census of Population and Housing — Details of Undercount, Aug 2006 (cat. no. 2940.0)

Census of Population and Housing — Undercount (cat. no. 2940.0)

Deaths, Australia (cat. no. 3302.0)

Demographic Estimates and Projections: Concepts, Sources and Methods (cat. no. 3228.0)

Experimental Estimates and Projections, Aboriginal and Torres Strait Islander Australians, 1991 to 2009 (cat. no. 3238.0)

Information Paper: Determining Seats in the House of Representatives - Legislative Requirements for Provision of ABS Statistics (cat. no. 3107.0.55.002)

Information Paper: Improved Methods for Estimating Net Overseas Migration (cat. no. 3107.0.55.003)

Information Paper: Measuring Net Undercount in the 2006 Population Census, 2007 (cat. no. 2940.0.55.001)

Information Paper: Statistical Implications of Improved Methods for Estimating Net Overseas Migration, Australia 2007 (cat. no. 3107.0.55.005)

Migration Australia (cat. no. 3412.0) – includes data on the country of birth of the ERP of Australia

Overseas Arrivals and Departures, Australia (cat. no. 3401.0) – issued monthly

Population by Age and Sex: Australian States and Territories (cat. no. 3201.0)

Population by Age and Sex, Australia (cat. no. 3235.0) – for sub state population data at SLA or LGA geographic levels

Population Projections, Australia (cat. no. 3222.0)

Regional Population Growth, Australia (cat. no. 3218.0)

ADDITIONAL STATISTICS AVAILABLE

20 As well as the statistics included in this and related publications, the ABS may have other relevant data available on request. Inquiries should be made to the National Information and Referral Service on 1300 135 070.

21 ABS products and publications are available free of charge from the ABS website <https://www.abs.gov.au>. Click on Statistics to gain access to the full range of ABS statistical and reference information.