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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 2006, 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:
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 2007 onwards are preliminary.
11 Selected birth estimates which were higher or lower than usual have been explained by the state registrars as follows:
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'. Estimates of NOM up to June quarter 2006, use the previous methods for estimating NOM (12/12 rule) unless specified as using the improved methodology for earlier periods. For further information on the new improved method see:
14 Prior to 1 July 2006, NOM estimation methods used a 12/12 rule to determine if a traveller contributed to ERP. This meant that in order for a person to contribute to NOM they must stay in or be absent from Australia for a continuous period of 12 out of 12 months. It compared data on actual travel movements over a 12 month period with data on individual travellers' duration of stay as recorded on their passenger cards. In order to conduct such a comparison, data for a 15 month period (i.e. one year plus one quarter) were required. For more detail see Demography Working Paper 2003/5 - Net Overseas Migration: Adjusting for Actual Duration of Stay or Absence (cat. no. 3137.0).
15 Australia's official population counts and estimates of NOM are to include all people, regardless of nationality or citizenship, who usually live in Australia, with the exception of foreign diplomatic personnel and their families. Therefore, foreign diplomatic personnel and their families are considered out of scope and need to be removed from NOM estimates. The previous methodology for estimating NOM was unable to exclude diplomatic personnel and their families. However, with the improved NOM methodology, refinements to the NOM processing system have enabled this to occur through the use of visa information. All diplomatic personnel and their families have been excluded from new NOM estimates for the reference period September quarter 2006 and onwards.
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 are 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 become 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 if it reduces intercensal error. 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 Changes to the model with updated expansion factors have now been applied to interstate migration estimates from September quarter 2006 onwards and will include the revision of preliminary estimates already published. The outcome of the review on the migration model is essentially the same as the previous model used to estimate interstate migration for 2001 to 2006. It includes updated expansion factors that have been calculated using the latest data available, including Census data and additional Medicare data used to help measure multiple movers (people who may have moved more than once during the year prior to the 2006 Census). Expansion factors are used to account for an under coverage of Medicare data by various ages and sex. The model includes the following characteristics:
19 For more detailed information on the changes to the model see Information Paper: Review of Interstate Migration Method, Mar 2009 (cat. no. 3106.0.55.001) to be released on the 18 March 2009.
20 Due to the fact that the Medicare data source is an indirect measure of interstate migration, the post-censal quarterly estimates of interstate migration have long been considered the weakest measure of a component of population change at the state and territory level. 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
21 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.
EXPERIMENTAL ESTIMATES OF ABORIGINAL AND TORRES STRAIT ISLANDER POPULATION
22 Estimates of the Indigenous population are experimental in that the standard approach to population estimation is not possible because satisfactory annual 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 of Aboriginal and Torres Strait Islander Australians, Jun 2006 (cat. no. 3238.0.55.001).
OVERSEAS ARRIVALS AND DEPARTURES STATISTICS
23 Persons arriving in, or departing from, Australia provide information in the form of incoming and outgoing passenger cards (see Appendix 1). Incoming persons also provide information in visa applications (apart from people travelling as Australian or New Zealand (NZ) 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. Following these changes, some questions on the passenger cards were not compulsory and answers to these questions were not checked by Customs officers. The question on marital status was deleted. Data on marital status is now derived from visa applications (only for certain visa classes) and is therefore not available for Australian or NZ citizens. The changes also affect the data for 'previous country of residence' which is imputed for Australian and NZ 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).
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 see Overseas Arrivals and Departures, Australia (cat. no. 3401.0).
NEW METHOD FOR DEFINING RESIDENTS TEMPORARILY OVERSEAS
28 The ABS has improved the measure of net overseas migration by expanding the Australian residence criteria from 12/12 months rule to 12/16 months rule (Information Paper: Improved Methods for estimating Net Overseas Migration, 2006 (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 12/16 month rule) could be observed.
29 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.
30 The ERP at June 2007 is the base for the projections series. The three series presented in this publication, and their assumptions are as follows:
31 Series A (high series) - assumes the Total Fertility Rate (TFR) will reach 2.0 babies per woman by 2021 and then remain constant, life expectancy at birth will continue to increase until 2056 (reaching 93.9 years for males and 96.1 years for females), NOM will reach 220,000 by 2011 and then remain constant, and high flows of interstate migration.
32 Series B (medium series) - assumes the TFR will decrease to 1.8 babies per woman by 2021 and then remain constant, life expectancy at birth will continue to increase each year until 2011 (reaching 85.0 years for males and 88.0 years for females) after which mortality improvement will decline until 2056, NOM will be held constant at 180,000 per year throughout the projection period, and medium flows of interstate migration.
33 Series C (low series) - assumes the TFR will decrease to 1.6 babies per woman by 2021 and then remain constant, life expectancy at birth will continue to increase each year until 2011 (reaching 85.0 years for males and 88.0 years for females) after which mortality improvement will decline until 2056, NOM will decrease to 140,000 per year by 2011 and then remain constant, and low flows of interstate migration.
34 For additional series and information (e.g. age, sex, states/territories and capital cities/balances of state) see Population Projections, Australia, 2006-2101 (cat. no. 3222.0).
35 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.
36 Data presented in tables 20 and 21 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). First household estimates based on the 2006 Census of Population and Housing (Census) and the final estimated resident population at 30 June 2006 are detailed on page 9 of this publication along with comparisons with the 2006 household projections based on the 2001 Census.
37 Estimates and projections of the number of households for years other than 2006 have not yet been compiled. As a result the household estimates presented in Tables 20 and 21 continue to be projections based on the 2001 Census. They are not comparable to the 2006 estimates presented on page 9. New estimates and projections based on the 2006 Census will be available 2010.
38 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.
39 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.
40 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.
41 Other ABS products which may be of interest to users include:
ADDITIONAL STATISTICS AVAILABLE
42 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.
43 ABS products and publications are available free of charge from the ABS website <http://www.abs.gov.au>. Click on Statistics to gain access to the full range of ABS statistical and reference information.
44 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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