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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 Census of Population and Housing held on 7 August 2001 (with various adjustments described in paragraph 4). The publication also contains estimates of the number of households by household size as well as the latest available statistics of births, deaths (including infant deaths) and overseas and interstate migration. In addition, the publication includes estimates of the resident population by age and region, population projections for Australia and experimental estimates and projections of the Aboriginal and Torres Strait Islander population. 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 7.

3 Estimates for Australian External Territories will be updated annually as at 30 June unless a more recent estimate is required for a determination 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 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.

6 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.

Natural increase: births and deaths

7 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 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).

Births and deaths data adjustment

8 Births and deaths data for the December quarter 2005 have been adjusted as set out in paragraphs 11 to 14 below. These adjustments include updated data for the numbers of births and deaths registered over the three previous 2005 quarters (March, June and September) and updated data for deaths registered in September and December quarters 2004. Therefore, any data used for analysis from births, deaths, natural increase or population growth for the December quarter 2005 should be used with caution.

9 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 2005 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 2005.

10 For the 2004-05 financial year, data will be released on a date of occurrence basis in Australian Demographic Statistics, March Quarter 2006 (cat. no. 3101.0) scheduled to be released on 21 September 2006.

Births data adjustment

11 In undertaking quality assurance of the latest available births data for the year ended 31 December 2005, a number of differences were found between the latest available data and those previously reported for compiling population estimates as at 30 September 2005. The differences between the number of births reported previously for March, June and September quarters 2005 and the most recent numbers can be attributed to:

• lags in coding births to overseas usually resident mothers,
• resolution of some issues associated with a new ABS processing system,
• lags in the provision of birth registrations to the ABS in time for preliminary estimates compilation,
• finalising coding of state and territory of usual residence, and
• removal of duplicate records.

BIRTHS, December quarter 2005 with adjustments
	BIRTHS REGISTERED	ADJUSTMENTS(a)				Births for ERP(b)
	Dec-05	Mar-05	Jun-05	Sep-05	Total	Updated Dec-05
NSW	22 832	3	0	-285	-282	22 550
Vic.	16 699	0	0	44	44	16 743
Qld	12 513	29	32	13	74	12 587
SA	4 263	0	0	13	13	4 276
WA	6 591	0	0	48	48	6 639
Tas.	1 544	62	0	55	117	1 661
NT	876	0	0	1	1	877
ACT	992	1	0	1	2	994
Aust.(c)	66 319	95	32	-110	17	66 336
(a) Comprises several adjustments - see text in Explanatory Notes 8-11 for details.
(b) Includes adjustments for March, June and September quarters 2005.
(c) Includes Other Territories.

Deaths data adjustment

13 Recently it was discovered that for SA and the ACT, some death registrations were not being received in the quarter of registration if there was no information in the cause of death field. These lagged registrations were subsequently provided to the ABS if and when the cause of death became available. Lagged death registrations have now been provided to the ABS and those from September quarter 2004 onwards have been included in the deaths registration adjustment. The remaining adjustments to records are late registrations received subsequently to the previous quarter, registrations for 2005 received in March 2006 data files, adjustments following processing of perinatal causes of death forms and removal of some duplicate records.

14 The table below shows a state breakdown of the adjustments which have been applied to December quarter 2005 deaths registrations. The updated December quarter 2005, includes adjustments to previously published deaths registrations for March, June and September quarters 2005 and for September and December quarters 2004.

DEATHS, December quarter 2005 with adjustments
	DEATHS REGISTERED(a)	ADJUSTMENTS(b)	Deaths for ERP(c)
	Dec-05	Total	Updated Dec-05
NSW	10 788	50	10 838
Vic.	9 056	137	9 193
Qld	4 951	7	4 958
SA	2 956	639	3 595
WA	2 797	-32	2 765
Tas.	913	2	915
NT	268	5	273
ACT	363	123	486
Aust.(d)	32 093	932	33 025
(a) Includes lagged death registrations for December quarter 2004.
(b) Comprises several adjustments - see text in Explanatory Notes 8-10 and 13 for details.
(c) Includes adjustments for March, June and September quarters 2005 and for lagged death registrations for September and December quarters 2004.
(d) Includes Other Territories.

Net overseas migration

15 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 Multicultural Affairs (DIMA). 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 determine the numbers of permanent and long-term arrivals, and permanent and long-term departures. Passenger card data are also used to calculate migration adjustments and determine the state and territory distribution of NOM. The processes of adjusting movement data on travellers' stated intentions to reflect their actual behaviour are complex, and depend upon the amount and type of movement data available at a particular point in time. The methods currently used compare data on actual travel movements over a one year period with those first 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) are required.

16 The adjustment methods described in the working paper have been applied to NOM data from the September quarter 2001 onwards and will be subject to further investigation and improvement with the accumulation of additional data and time series. For more information see the Technical Note - Measuring Net Overseas Migration.

Net interstate migration

17 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, see the Demography Working Paper: 2004/1 Review of Interstate Migration Method (cat.no. 3106.0.55.001).

CORRECTION OF PRISON DATA FOR QUEENSLAND

18 For the 2001 Census of Population and Housing, most prison data was received for processing via electronic data files. During the post-processing evaluation cycle, it was established that the male and female counts for Queensland prisons (only) were incorrectly captured. This resulted in the publication of incorrect census counts for males and females for various Queensland geographical areas and, as a consequence the incorrect numbers for males and females for Queensland and Australia. Revised population estimates for the 2001-02 financial year phased in a correction for this error. Information on the geographical areas affected are available in the 2001 Census Working Paper-Fact Sheet: Correction of Prison Data for Queensland
.

RATES OF POPULATION GROWTH

19 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

20 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, 1991 to 2009 (cat. no. 3238.0).

EXPERIMENTAL PROJECTIONS OF ABORIGINAL AND TORRES STRAIT ISLANDER POPULATION

21 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 to 2009 (cat. no. 3238.0).

ESTIMATED RESIDENT HOUSEHOLDS

22 Estimates of households are based on the estimated resident population series, to which propensities to form households are applied. These propensities were estimated from the Census of Population and Housing, and updated using the monthly Labour Force Survey. A detailed description of the method used to produce household estimates is contained in Household Estimates 1986, 1991-94 (cat. no. 3229.0).

OVERSEAS ARRIVALS AND DEPARTURES ESTIMATION METHOD

23 Overseas arrival and departure statistics are derived from a combination of full enumeration and sampling. All permanent movements and all movements with a duration of stay of one year or more are fully enumerated and processed. All movements with a duration of stay of less than one year are sampled. Statistics relating to these movements are therefore estimates which may differ from statistics which would have been obtained if details of all these movements had been processed.

24 From July 1998 DIMA has been able to determine the actual length of stay for departing overseas visitors and arriving Australian residents previously collected from information on intended length of stay supplied on the arrival or departure card by the passenger. This new method has resulted in a change in data distribution with the number of passengers staying for one year exactly declining significantly.

POPULATION PROJECTIONS

25 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.

26 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).

28 Where figures have been rounded, discrepancies may occur between sums of component items and totals.

RELATED PRODUCTS

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

• Australian Demographic Trends (cat. no. 3102.0).
• Australian Historical Population Statistics (cat. no. 3105.0.65.001)
• Births, Australia (cat. no. 3301.0)
• Deaths, Australia (cat. no. 3302.0)
• Demographic Estimates and Projections: Concepts, Sources and Methods (cat.no. 3228.0).
• Divorces, Australia (cat. no. 3307.0.55.001)
• Experimental Estimates and Projections, Aboriginal and Torres Strait Islander Australians, 1991 to 2009 (cat. no. 3238.0)
• Household Estimates, Australia (cat. no. 3229.0).
• Information Paper: Census of Population and Housing, Data Quality - Undercount, Australia, 2001 (cat. no. 2940.0)
• Information Paper: Determining Seats in the House of Representatives - Legislative Requirements for Provision of ABS Statistics (cat.no. 3107.0.55.002)
• Marriages, Australia (cat. no. 3306.0.55.001) - includes data on the marital status of the ERP of Australia
• 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 Projections, Australia (cat. no. 3222.0)
• Regional Population Growth, Australia (cat. no. 3218.0)
• Underlying Cause of Death by Sex and Age at Death, State of Usual Residence and ICD-10 - from 1999 (cat no. 3303.0 Causes of Death)

31 AusStats is a web based information service which provides ABS full standard product range online. It also includes companion data in multidimensional datasets in SuperTABLE format, and time series spreadsheets.

32 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.

33 Statistics of overseas arrivals and departures and related data are also published regularly by DIMA (see the Department’s quarterly publication, Immigration Update) and by the Tourism Research Australia (on international travel and tourism).