EXPLANATORY NOTES
INTRODUCTION
1 This quarterly publication contains the most recent estimates of the resident populations (ERP) of Australia and the states and territories based on the results of the 2006 Census of Population and Housing held on 8 August 2006 (with various adjustments described in paragraph 5). The ABS has used the 2006 Census to produce revised rebased estimates of the resident population (refer to paragraph 6). The publication contains the latest available statistics on births, deaths (including infant deaths) and overseas and interstate migration. In addition, the publication includes estimates of the resident population by age groups, major population regions and experimental estimates and projections of the Aboriginal and Torres Strait Islander population. It also includes projected resident populations, projected number of households and projected average household size. Periodically, articles on specific demographic topics will be released on the ABS web site in conjunction with this publication.
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 which were previously excluded from population estimates for Australia. Data for Other and External Territories are detailed separately in Table 9.
3 Estimates for Australian External Territories will be updated annually as at 30 June unless a more recent estimate is required for electoral apportionment purposes under the Commonwealth Electoral Act 1918.
POPULATION AND COMPONENTS OF POPULATION CHANGE
4 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
5 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 component of natural increase (on a usual residence basis) and the component of 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 Census net undercount and the number of Australian residents estimated to have been temporarily overseas at the time of the Census. Overseas visitors in Australia are excluded from this calculation.
6 After each Census, 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.
Status of quarterly ERP data
7 The status of quarterly ERP data changes over time from preliminary to revised to final. The following table shows the current status of ERP and the components of population change: natural increase, net overseas migration and net interstate migration.
Natural increase: births and deaths
8 Natural increase is a major component of ABS quarterly state and territory population estimates and is calculated using the estimated number of births and deaths. The births and deaths data in this release are shown by state and territory of usual residence, using year/quarter of registration for preliminary data and year/quarter of occurrence for both revised and final data. This may affect time series comparisons 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 those occurrences which were yet to be registered at the time of revision. For final estimates between 30 June 1991 and 30 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.
10 Preliminary births and deaths estimates are subject to fluctuations caused by lags or accumulations in the reporting of births and deaths registrations. Accumulations can result from the eventual processing of lagged registrations in a later quarter. As a result, preliminary quarterly estimates can be an underestimate or an overestimate of the true numbers of births and deaths occurring in a reference period. Note that estimates from September quarter 2006 onwards are preliminary.
Births and deaths data adjustment
11 Adjustments were applied to December quarter 2006 births and deaths registrations in the previous issue of this publication to produce an accurate estimated resident population at 31 December 2006. These adjustments included the numbers of births and deaths registered over the three previous 2006 quarters (March, June and September). Adjustments applied to December quarter 2006 births and deaths registrations have been updated and are now shown in their correct quarters.
12 Further, in this issue the scheduled annual revisions for each quarter of the 2005-06 financial year were undertaken, revising all births and deaths (based on occurrence) for this time period. Preliminary births and deaths (based on registration) for September and December quarters 2006, have also been updated as mentioned in the paragraph above.
Net overseas migration
13 Conceptually, net overseas migration (NOM) is the difference between permanent and long-term arrivals, and permanent and long-term departures. Estimates of NOM are derived from information provided on incoming and outgoing passenger cards, as well as other data supplied by the Department of Immigration and Citizenship (DIAC), formerly the Department of Immigration and Multicultural Affairs (DIMA) and the Department of Immigration and Multicultural and Indigenous Affairs (DIMIA). Data on the intended duration of stay of overseas visitors arriving in Australia and the intended duration of absence of Australian residents travelling overseas are used to initially determine the numbers of permanent and long-term arrivals, and permanent and long-term departures. Passenger card data are then used to calculate migration adjustments and determine the state and territory distribution of NOM.
14 The Australian Bureau of Statistics (ABS) has developed an improved method for calculating NOM for September quarter 2006 onwards. Estimates from the past time series based on the previous method, and the current time series based on the improved method are not comparable. Preliminary estimates for September quarter 2006 onwards based on the new method are included in Table 2 of this issue. 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 (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).
15 The previous method used to estimate net overseas migration from September quarter 2001 to June quarter 2006 compared data on actual travel movements over a one year period with those advised by individual travellers, and are explained in more detail in Demography Working Paper 2003/5 - Net Overseas Migration: Adjusting for Actual Duration of Stay or Absence (cat. no. 3137.0). In order to conduct such a comparison, data for a 15 month period (i.e. one year plus one quarter) were required.
Net interstate migration
16 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.
17 When Census data on interstate movement becomes available part of the process of rebasing ERPs for states and territories is the re-derivation of interstate migration for the intercensal period. The overall approach is to minimise state intercensal error using data analysed from the Census questions concerning an individual's place of residence one-year ago, five-years ago and at Census night. When new Census data are available, interstate migration estimates for the intercensal period are replaced with estimates derived from Census data on place of usual residence five years ago. These estimates are then scaled so that they sum to zero at the Australian level. A similar process is carried out for the year prior to the Census, using Census data on place of usual residence one year ago. The difference between the original interstate migration estimates and the rebased estimates is apportioned across all quarters, movement categories, ages and sex categories in the intercensal period in order to minimise quarterly change.
18 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
19 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
20 The average annual growth rate, r, is calculated as a percentage using the formula
r = 
where P0 is the population at the start of the period, Pn is the population at the end of the period and n is the length of the period between Pn and P0 in years.
EXPERIMENTAL ESTIMATES OF ABORIGINAL AND TORRES STRAIT ISLANDER POPULATION
21 Estimates of the Indigenous population are experimental in that the standard approach to population estimation is not possible because satisfactory data on births, deaths and internal migration are not generally available. Furthermore, there is significant intercensal volatility in census counts of the Indigenous population, thus adding to the problem of estimating the true Indigenous population. This volatility can in part be attributed to changes to the Indigenous population that can not be attributed to natural increase or interstate migration. As a result, a method based on the use of life tables is used to produce time series data. For further details see Experimental Estimates and Projections, Aboriginal and Torres Strait Islander Australians (cat. no. 3238.0).
EXPERIMENTAL PROJECTIONS OF ABORIGINAL AND TORRES STRAIT ISLANDER POPULATION
22 Experimental estimates of the Indigenous population as at 30 June 2001 are used as the base population for projections of the Indigenous population to 30 June 2009. A low and a high projection series have been generated, and respectively imply a low and high overall growth rate of the Indigenous population. The low series assumes a change to the Indigenous population is a result of natural increase and, for states and territories, a result of interstate migration. The high series assumes an increase in the Indigenous population observed between the 1996 and 2001 Censuses which cannot be attributed to natural increase. For further details see Experimental Estimates and Projections, Aboriginal and Torres Strait Islander Australians, 1991-2009 (cat. no. 3238.0).
OVERSEAS ARRIVALS AND DEPARTURES STATISTICS
23 Persons arriving in, or departing from Australia provide information in the form of incoming and outgoing passenger cards. Incoming persons also provide information in visa applications, apart from people travelling as Australian and New Zealand citizens. These and other information available to the Department of Immigration and Citizenship (DIAC) serve as a source for statistics of overseas arrivals and departures (OAD).
24 In July 1998, DIAC revised the incoming and outgoing passenger cards and associated procedures as well as computer systems. Some questions which obtained information already stored in the DIAC Travel and Immigration Processing System (TRIPS) (e.g. sex and marital status) were deleted. Data for the deleted questions and some other missing data (for unanswered questions or missing data) is obtained from the DIAC TRIPS. The changes also affect the data for 'previous country of residence' which is imputed for Australian and New Zealand citizens. For more information see the May 1998 issue of Overseas Arrivals and Departures, Australia (cat. no. 3401.0). Since July 1998, there have been additional minor changes to both incoming and outgoing passenger cards.
25 From July 2001, DIAC adopted a new passenger card processing system which involved electronic imaging of passenger cards and intelligent character recognition of the data stored in the images. This process has yielded several improvements to the processing of passenger card data, most notably the detailed information about missing values. There have also been several changes to data quality. Further information on these changes is provided in Overseas Arrivals and Departures, Australia (cat. no. 3401.0).
Scope
26 Overseas arrivals and departures statistics relate to the number of movements of travellers rather than the number of travellers (i.e. multiple movements of individual persons during a given reference period are each counted separately). The statistics exclude the movements of operational air and ships' crew, of transit passengers who pass through Australia but are not cleared for entry, and of passengers on pleasure cruises commencing and finishing in Australia. Similarly, these statistics exclude unauthorised arrivals.
27 For more information on overseas arrivals and departures see Overseas Arrivals and Departures, Australia (cat. no. 3401.0).
POPULATION PROJECTIONS
28 Population projections presented in this publication are not predictions or forecasts. They are an assessment of what would happen to Australia's population if the assumed levels of components of population change - births, deaths and migration - were to hold for the next 50-100 years.
29 The ERP at June 2004 is the base for the projections series. The three series presented in this publication, and their assumptions are as follows:
- Series A (high series) - assumes the TFR will reach 1.9 babies per woman by 2018 and then remain constant, life expectancy at birth will continue to increase until 2050-51 (reaching 92.7 years for males and 95.1 years for females), NOM will reach 140,000 by 2007-08 and then remain constant, and high flows of interstate migration.
- Series B (medium series) - assumes the TFR will decrease to 1.7 babies per woman by 2018 and then remain constant, life expectancy at birth will continue to increase each year until 2050-51, though at a declining rate (reaching 84.9 years for males and 88.0 years for females), NOM will be held constant at 110,000 per year throughout the projection period, and medium flows of interstate migration.
- Series C (low series) - assumes the TFR will decrease to 1.5 babies per woman by 2018 and then remain constant, life expectancy at birth will continue to increase each year until 2050-51, though at a declining rate (reaching 84.9 years for males and 88.0 years for females), NOM will reach 80,000 per year by 2007-08 and then remain constant, and low flows of interstate migration.
For additional series and information (e.g. age, sex, states/territories and capital cities/balances of state) see Population Projections, Australia, 2004-2101 (cat. no. 3222.0).
HOUSEHOLD PROJECTIONS
30 The ABS uses a propensity method to project numbers of households, families and living arrangements. The method identifies propensities (i.e. proportions) for people to belong to different living arrangement types from the Census of Population and Housing.
Trends observed in propensities over the last four Censuses are then projected forward and applied to a projected total population see; Series II,
Population Projections, Australia, 2002 to 2101 (cat. no. 3222.0). From these projections of living arrangements, projected numbers of families and households are derived.
31 Data presented in tables 19 and 20 are not intended as predictions or forecasts, but are illustrations of growth and change in the numbers of households and average household size which would occur if the assumptions about future trends in living arrangements were to prevail over the projection period. For more information see Household and Family Projections, Australia, 2001 to 2026 (cat. no. 3236.0).
CONFIDENTIALITY
32 The Census and Statistics Act, 1905 provides the authority for the ABS to collect statistical information, and requires that statistical output shall not be published or disseminated in a manner that is likely to enable the identification of a particular person or organisation. This requirement means that the ABS must take care and make assurances that any statistical information about individual respondents cannot be derived from published data.
33 Some techniques used to guard against identification or disclosure of confidential information in statistical tables are suppression of sensitive cells, and random adjustments to cells with very small values. To protect confidentiality within this publication, some cell values may have been suppressed and are not available for publication (np) but included in totals where applicable. In these cases data may not sum to totals due to the confidentialisation of individual cells.
ROUNDING
34 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.
ADDITIONAL STATISTICS AVAILABLE
35 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.
36 Current publications and other products released by the ABS are listed in the Catalogue of Publications and Products (cat. no. 1101.0). The Catalogue is available from any ABS office or the ABS web site. The ABS also issues a daily Release Advice on the web site which details products to be released in the week ahead.
37 Statistics of overseas arrivals and departures and related data are also published regularly by DIAC (see the Department’s quarterly publication, Immigration Update) and by the Tourism Research Australia (on international travel and tourism).
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