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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 2011, year/quarter of occurrence data are used. For further details see Demography Working Paper 1998/2 - Quarterly Birth and Death Estimates, 1998 (cat. no. 3114.0).
9 The timeliness and accuracy of ABS quarterly population estimates depend 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:
10 Preliminary birth and death 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.
11 Selected birth and death registration data contributing to preliminary estimates which are higher or lower than usual have been explained by the state registrars as follows:
Net overseas migration
12 According to recommendations of the United Nations, an international migrant is defined as "any person who changes his or her country of usual residence" (United Nations 1998). For the purposes of estimating net overseas migration (NOM), and thereby Australia's official ERP counts, a person is regarded as a usual resident if they have been (or expected to be) residing in Australia for a period of 12 months or more over a 16-month period. As such, NOM and ERP estimates include all people, regardless of nationality, citizenship or legal status, who usually live in Australia, with the exception of foreign diplomatic personnel and their families.
13 Conceptually, the term NOM is based on an international traveller's 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). With the introduction of the improved methods for estimating NOM, this 12 month period does not have to be continuous and is measured over a 16-month reference period. Therefore, whether a traveller is in or out of the population is determined by their exact duration of stay in or away from Australia over the subsequent 16 months after arrival or departure.
14 After reviewing the treatment of temporary migrants (both long-term and short-term) who are away from or resident in Australia for a period of 12 months or more, the ABS developed and introduced an improved NOM processing method, called the '12/16 month rule', for estimating NOM. It has been used in calculating Australia's official ERP since September quarter 2006. This represents a break in series and therefore NOM estimates from earlier periods are not comparable.
15 The current NOM estimation methods employ a '12/16 month rule' where the traveller can be added or subtracted from NOM if they have stayed in or been absent from Australia for a period of 12 months or more over a 16-month period. This period of 12 months does not have to be continuous. Although a traveller states their intended duration of stay on a passenger card, for NOM purposes the ABS now measures an individual's actual travel behaviour.
16 For further information on the improvements to NOM estimation and changes to the revision schedule for NOM, see the Information Paper: Improving Net Overseas Migration Estimation, Mar 2010 (cat. no. 3412.0.55.001). For further information on the '12/16 month rule' methodology see the Technical Note: '12/16 month rule' Methodology for Calculating Net Overseas Migration from September quarter 2006 onwards in Migration, Australia, 2009-10 (cat. no. 3412.0). For more detailed information, see:
Final NOM estimates
17 It is with the final NOM estimates that the '12/16 month rule' can be fully applied. A traveller's actual duration of stay can only be calculated when data on overseas movements become available for the 16 months following a reference period. Final NOM estimation methods use ERP flags to determine if a traveller, through their actual duration of stay in or out of Australia, should be included or excluded from NOM estimates and consequently ERP estimates.
Preliminary NOM estimates
18 Preliminary estimates of NOM are required five to six months after the reference quarter for the production of quarterly estimates of the population of Australia, and the states and territories. At that time, complete traveller histories for the 16 months following a reference quarter cannot be produced. Since September quarter 2008, migration adjustments have been calculated from changes in behaviour from final estimates one year earlier for the same groups of travellers. These migration adjustments are applied to travellers who are grouped according to their 'initial category of travel', age, country of citizenship and state/territory of usual/intended residence. The adjustments account for differences between their intended duration of stay and their actual duration of stay. However, due to the unavailability of passenger card data for the December quarter 2014, the previous two-year ago propensity model (as described in note 19 below) has been used to estimate preliminary NOM for September quarter 2014. Based on historical comparisons of the two methods, this change is not expected to result in larger than usual revisions when final NOM estimates become available.
19 Preliminary estimates using an improved method for estimating NOM using a 'two year ago' propensity model were used in official ABS population estimates from September quarter 2006 until June quarter 2008. Since September quarter 2008 a 'one year ago' propensity model has been used.
20 Australia's ERP and estimates of NOM 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 were removed from NOM estimates from 1 July 2006. The previous methodology for estimating NOM was unable to exclude diplomatic personnel and their families.
Net interstate migration
21 Interstate migration is a key determinant of the accuracy of state and territory population estimates. Data on interstate migration cannot 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 from Medicare Australia and 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.
22 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 preliminary intercensal difference using data analysed from the Census questions concerning an individual's place of residence one year ago, five years ago and on 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 these reduce preliminary intercensal difference. These estimates are then scaled to 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.
23 Changes to the model with updated expansion factors based on Census and other Medicare data are applied after each Census. Expansion factors are used to account for an undercoverage of Medicare data by various ages and sex. The current model is essentially unchanged from the model used to estimate interstate migration between 2006 to 2011 but for updated expansion factors based on the 2011 Census. The model includes the following characteristics:
24 The previously modelled data for the period September 2006 to June 2011 has been finalised based on data from the 2011 Census. All data from September 2011 onwards is modelled on 2011 Census expansion factors.
25 For more detailed information on the changes to the model see Information Paper: Review of Interstate Migration Method, March 2014 (cat. no. 3412.0.55.003).
26 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 the components 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:
Defence force adjustment
27 Medicare theoretically covers all Australian usual residents as well as those non-Australian residents granted temporary Medicare 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 Information Paper: Review of Interstate Migration Method, March 2014 (cat. no. 3412.0.55.003) 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.
ESTIMATES AND PROJECTIONS OF ABORIGINAL AND TORRES STRAIT ISLANDER POPULATION
28 The standard approach to population estimation is not possible for determining the population of Aboriginal and Torres Strait Islander Australian. There are two primary reasons for this: the significant volatility in Aboriginal and Torres Strait Islander Census counts between censuses which cannot be attributed to demographic factors (i.e. the difference cannot be fully accounted for by natural increase and migration over the intercensal period); and the quality of data on births, deaths and migration specific to Aboriginal and Torres Strait Islander people. As a result, a method based on the use of life tables and rates of net interstate migration derived from the Census is used to backcast the series. Aboriginal and Torres Strait Islander estimates, based on the 2011 Census for the period 1996 to 2011, and projections from 2012 to 2026 are available in Estimates and Projections, Aboriginal and Torres Strait Islander Australians, 2001 to 2026 (cat. no. 3238.0). Three main projection series were produced with assumptions as follows. Projections Series A assumes: constant fertility rates; 2% annual increase in paternity rates (where the father of a child is Aboriginal or Torres Strait Islander but the mother is not); life expectancy at birth increasing by 0.5 years per year for males and 0.45 years per year for females, reaching 76.5 years for males and 80.4 years for females by 2026; levels of interstate migration as observed in the 2011 Census; and zero net overseas migration. Projection Series B assumes: an annual decrease of 0.5% in fertility rates; 1% annual increase in paternity rates; life expectancy at birth increasing by 0.3 years per year for males and 0.25 years per year for females, reaching 73.5 years for males and 77.4 years for females by 2026; levels of interstate migration as observed in the 2011 Census; and zero net overseas migration. Projection Series C assumes: an annual decrease of 1.0% in fertility rates; constant paternity rates; life expectancy at birth increasing by 0.2 years per year for males and 0.15 years per year for females, reaching 72.0 years for males and 75.9 years for females by 2026; levels of interstate migration as observed in the 2011 Census; and zero net overseas migration.
METHOD FOR DEFINING RESIDENTS TEMPORARILY OVERSEAS
29 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. This has implications for the measurement of residents temporarily overseas (RTOs) due to the change in residence criteria mentioned above. A final measure of RTOs can 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) can be observed. For further information on the improved measure of net overseas migration see:
30 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.
31 The ERP at June 2012 based to the 2011 Census is the base for the projections series. Projections off the 2011 Census based ERP were released on 26 November 2013 in "Population Projections, Australia, 2012 (base) to 2101" (cat. no. 3222.0). The three series presented in this publication, and their assumptions are as follows:
32 Series A - assumes the Total Fertility Rate (TFR) will reach 2.0 babies per woman by 2026 and then remain constant, life expectancy at birth will experience continued improvement with increases from 2009-11 levels of 0.25 and 0.19 years each year for males and females respectively until 2060-61 (reaching 92.1 years for males and 93.6 years for females), NOM will increase to 280,000 people per year by 2020-21 and remain constant thereafter, and relatively large net interstate migration gains for some states and territories, corresponding to relatively large losses for other states and territories.
33 Series B - assumes the TFR will decline to 1.8 babies per woman by 2026 and then remain constant, life expectancy at birth will experience declining improvement with increases from 2009-11 levels of 0.25 and 0.19 years each year for males and females respectively until 2015-16 after which life expectancy will continue to increase at declining rates (reaching 85.2 years for males and 88.3 years for females by 2060-61), NOM will increase to 240,000 people per year by 2020-21 and remain constant thereafter, and medium net interstate migration gains for some states and territories, and medium losses for others.
34 Series C - assumes the TFR will decline to 1.6 babies per woman by 2026 and then remain constant, life expectancy at birth will experience declining improvement with increases from 2009-11 levels of 0.25 and 0.19 years each year for males and females respectively until 2015-16 after which life expectancy will continue to increase at declining rates (reaching 85.2 years for males and 88.3 years for females by 2060-61), NOM will increase to 200,000 people per year by 2020-21 and then remain constant thereafter, and relatively small net interstate migration gains for some states and territories and small losses for others.
35 For additional series and information (e.g. age, sex, states/territories and greater capital cities/balances of state), see Population Projections, Australia, 2012 (base) to 2101 (cat. no. 3222.0).
36 The ABS uses a propensity method to project numbers of households, families and persons in different living arrangements. The method identifies propensities (proportions) from the Census of Population and Housing for people to belong to different living arrangement types. Trends observed in the propensities over the last four censuses are assumed to continue into the future, and applied to a projected population (see Series B, Population Projections, Australia, 2012 (base) to 2101 (cat. no. 3222.0)). Numbers of households and families are then derived from the projected living arrangements of the population.
37 Data presented in table 18 are not intended as predictions or forecasts, but are illustrations of growth and change in the numbers of households 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, 2011 to 2036 (cat. no. 3236.0). Household projections presented in this publication are based on the 2006 Census.
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 ABS publications draw extensively on information provided freely by individuals, businesses, governments and other organisations. Their continued cooperation is very much appreciated: without it, the wide range of statistics published in the ABS would not be available. Information received by the ABS is treated in strict confidence as required by the Census and Statistics Act 1905.
USE OF POPULATION ESTIMATES IN AGREEMENTS
42 The ABS is the central statistical authority for the Australian government. It is required by law to publish official population estimates. It abides by codes of professional practice that include being open and transparent about underlying methodology. The ABS provides regular explanatory information to support users in understanding both population trends and methodological changes, but does not comment on the specific use (or otherwise) of official population estimates by other organisations or individuals.
43 Population estimates are used extensively within the Australian community, including in a range of agreements. Although the ABS acknowledges that the official population estimates and changes in these estimates are specifically referenced in various agreements, it neither endorses nor disapproves of the terms of the agreements and decisions made by parties in relation to those agreements. In addition, the ABS does not provide a position on disputes arising from the interpretation of terms of an agreement that reference official population estimates.
44 Other ABS products which may be of interest to users include:
ADDITIONAL STATISTICS AVAILABLE
46 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.
47 Statistics of net overseas migration and related data are also published regularly by DIBP <http://www.immi.gov.au> (see the Department’s quarterly publications, Immigration Update and The Outlook for Net Overseas Migration).
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