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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 4). The ABS has used the 2006 Census to produce preliminary 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, previously excluded from population estimates for Australia. Data for Other and External Territories are detailed separately in Table 8.

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 ERP data

7 The status of 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.

Status of Estimated Resident Population Data - as at 5 June 2007
Reference period	Estimated resident population	Natural increase	Net overseas migration	Net interstate migration
1996-2001 intercensal period
Sep. 1996-Jun. 1997	Final rebased, based on 2001 Census	Final	Final	Final, rebased to 2001 Census
Sep. 1997-Jun. 2001	Final rebased, based on 2001 Census	Final	Final, category jumping set to zero	Final, rebased to 2001 Census
2001-2006 intercensal period
Sep. 2001-Jun. 2005	Preliminary rebased, based on 2006 Census	Revised, based on date of occurrence	Final, includes migration adjustment using matched passenger cards	Preliminary, modelled - expansion factors based on 2001 Census
Sep. 2005-Jun. 2006	Preliminary rebased, based on 2006 Census	Preliminary, based on date of registration	Preliminary, migration adjustment based on ratios observed in 2004-05. State distribution of migration adjustment based on permanent and long-term arrivals for period.	Preliminary, modelled - expansion factors based on 2001 Census
2006-2011 intercensal period
Sep. 2006-Dec. 2006	Preliminary, based on 2006 Census	Preliminary, based on date of registration	Improved method of NOM introduced and used for Sep. quarter 2006 onwards. Preliminary NOM estimates are based on international movement data for the reference quarter, adjusted by information derived from travellers with the same characteristics from the corresponding quarter two years earlier.	Preliminary, modelled - expansion factors based on 2001 Census

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.

Births and deaths data adjustment

11 Births and deaths data for the December quarter 2006 have been adjusted as set out in paragraphs 14 to 17 below. These adjustments include updated data for the numbers of births and deaths registered over the three previous 2006 quarters (March, June and September). Therefore, any data used for analysis from births, deaths, natural increase or population growth for the December quarter 2006 should be used with caution.

12 The standard annual revision to preliminary data (including births, deaths, natural increase and population growth) is scheduled for the next edition of this publication. Adjustments were applied to December quarter 2006 births and deaths registrations, rather than the correct quarters to minimise confusion arising from undertaking two consecutive revisions. These adjustments were applied to this quarter to produce a more accurate estimated resident population at 31 December 2006.

13 For the 2005-06 financial year, data will be released on a date of occurrence basis in Australian Demographic Statistics, March quarter 2007 (cat. no. 3101.0) scheduled to be released on 24 September 2007.

Births data adjustment

14 In undertaking quality assurance of the latest available births data for the year ended 31 December 2006, a number of differences were found between the latest available data and those previously reported for compiling population estimates as at 30 September 2006. The differences between the number of births reported previously for March, June and September quarters 2006 and the most recent numbers can be attributed to:

• resolution of the effects of the implementation of a new births processing system by the Tasmanian Registry;
• removal of duplicate records;
• removal of out-of-scope records;
• lags in birth registrations; and
• finalising coding of state and territory of usual residence.

BIRTHS, December quarter 2006 with adjustments
	Births registered	Adjustments(a)				Births for ERP(b)
	Dec-06	Mar-06	Jun-06	Sep-06	Total	Updated Dec-06
NSW	23 577	24	-306	1	-281	23 296
Vic.	17 567	0	-19	0	-19	17 548
Qld	12 676	3	4	17	24	12 700
SA	4 344	9	8	3	20	4 364
WA	7 061	2	3	4	9	7 070
Tas.	1 711	-5	0	-165	-170	1 541
NT	929	-2	-7	-17	-26	903
ACT	977	-8	-2	-1	-11	966
Aust.(c)	68 852	23	-319	-158	-454	68 398
(a) Difference between figures previously reported and the latest available data.
(b) Includes adjustments for March, June and September quarters 2006.
(c) Includes Other Territories.

Deaths data adjustment

16 A number of differences were found between the latest available deaths data for the December quarter 2006 and those previously reported for compiling population estimates as at 30 September 2006. The differences between the number of deaths reported previously for March, June and September quarters 2006 and the most recent numbers can be attributed to:

• removal of duplicate records;
• lags in death registrations; and
• removal of out-of-scope records, including overseas deaths.

DEATHS, December quarter 2006 with adjustments
	Deaths registered	Adjustments(a)				Deaths for ERP(b)
	Dec-06	Mar-06	Jun-06	Sep-06	Total	Updated Dec-06
NSW	10 787	4	28	4	36	10 823
Vic.	9 858	-4	0	7	3	9 861
Qld	5 645	13	6	2	21	5 666
SA	2 841	4	4	1	9	2 850
WA	2 951	1	5	-2	4	2 955
Tas.	922	4	0	2	6	928
NT	247	3	3	5	11	258
ACT	356	3	1	0	4	360
Aust.(c)	33 610	28	47	19	94	33 704
(a) Difference between figures previously reported and the latest available data.
(b) Includes adjustments for March, June and September quarters 2006.
(c) Includes Other Territories.

Net overseas migration

18 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.

19 The Australian Bureau of Statistics (ABS) has developed an improved method for calculating net overseas migration (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 and December quarters 2006 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 current '12/12 month rule'. For further information on the new 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).

20 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

21 Estimates of interstate migration since June 1986 have been derived from the latest Census data on interstate movement in the preceding one year and unidentified information on interstate changes of address advised to Medicare Australia in the process of administering Medicare. Medicare Australia came into operation on 1 October 2005, and now performs all the functions and provides all the services that were previously administered by the Health Insurance Commission. 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

22 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

23 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, P_n is the population at the end of the period and n is the length of the period between P_n and P₀ in years.

EXPERIMENTAL ESTIMATES OF ABORIGINAL AND TORRES STRAIT ISLANDER POPULATION

24 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

25 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

26 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).

27 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.

28 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

29 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.

30 For more information on overseas arrivals and departures see Overseas Arrivals and Departures, Australia (cat. no. 3401.0).

POPULATION PROJECTIONS

31 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.

32 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).

34 Data presented in tables 17 and 18 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).

ROUNDING

35 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

36 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.

37 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.

38 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).