EXPLANATORY NOTES


INTRODUCTION

1 This quarterly release contains the most recent estimates of the resident populations (ERP) of Australia and the states and territories based on the results of the 2016 Census of Population and Housing held on 9 August 2016 (with various adjustments described in paragraphs 5 and 6), and the addition of quarterly components of population growth. The ABS has used the 2016 Census to produce final rebased estimates of the resident population (refer to paragraph 6). This release contains the latest available statistics on births, deaths (including infant deaths) and overseas and interstate migration. In addition, the release includes estimates of the resident population by age groups, major population regions and estimates and projections of the Aboriginal and Torres Strait Islander population. It also includes projected resident populations (2011 base) and estimated number of households (2016 base). Periodically, articles on specific demographic topics will be released on the ABS web site in conjunction with this release.

2 Population estimates commencing from September quarter 1993 include estimates for another category of the state and territory level, 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. From 1 July 2016 Norfolk Island has been included in the Other Territory category following the introduction of the Norfolk Island Legislation Amendment Act 2015. Data for Other and External Territories are detailed separately in table 3.

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 Information Paper: Population Concepts, 2008 (cat. no. 3107.0.55.006) and also in Population Estimates: Concepts, Sources and Methods, 2009 (cat. no. 3228.0.55.001).


Method of estimation

5 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 on Census night. Overseas visitors in Australia on Census night are excluded in this calculation. Post-Census ERP is 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, estimated interstate movements involving a change of usual residence are also taken into account.

6 After each Census, estimates for the preceding intercensal period are finalised (rebased) by incorporating an additional adjustment (intercensal difference) to ensure that the difference between the ERPs at the two 30 June dates in the respective Census years agrees with the total intercensal change.


Status of quarterly ERP data

7 The status of quarterly ERP data changes over time from preliminary to revised to final as new component data becomes available. ERP is updated most quarters due to revisions to the component data for earlier quarters, but will only change status to revised once both natural increase and net overseas migration for that quarter have a status of revised. The table below shows the current status of ERP and the components of population change: natural increase, overseas migration and interstate migration.

Status of quarterly Estimated Resident Population (ERP) data, as at 20 September 2018
	Census base	Natural increase	Overseas migration	Interstate migration	ERP STATUS
Sep.1991-Jun. 2016	Based to 1996, 2001, 2006, 2011 & 2016 Censuses as applicable	Final	Final	Final	FINAL
Sep. 2016-Mar. 2017	2016 Census	Revised - based on date of occurrence	Final - based on actual traveller behaviour	Preliminary - based on modelled expansion factors from 2016 Census	REVISED
Jun. 2017	2016 Census	Revised - based on date of occurrence	Preliminary - based on modelled traveller behaviour	Preliminary - based on modelled expansion factors from 2016 Census	PRELIMINARY - updated due to revised component data
Sep. 2017-Dec. 2017	2016 Census	Preliminary - based on date of registration	Preliminary - based on modelled traveller behaviour	Preliminary - based on modelled expansion factors from 2016 Census	PRELIMINARY - updated due to revised component data
Mar. 2018	2016 Census	Preliminary - based on date of registration	Preliminary - based on modelled traveller behaviour	Preliminary - based on modelled expansion factors from 2016 Census	PRELIMINARY

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.

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 provide timely estimates, the ABS produces preliminary estimates using births and deaths by quarter of registration 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. The major difficulty in this area is that while the vast majority of births and deaths are registered promptly, a small proportion of registrations are delayed for months or even years.

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. Lags or accumulations in births and deaths registrations can be caused by:

• 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; or
• resolution of issues that may arise within the ABS or registry processing systems.

11 Birth and death registration data contributing to preliminary estimates which are higher or lower than usual are noted below along with any explanations provided by the relevant state or territory registrars:

• December 2017: New South Wales. The ABS has worked with the NSW Registry of Births, Deaths and Marriages to understand the reasons for lower than expected registration counts in recent quarters. The NSW Registry have responded to this issue, enabling additional registrations to be included in the December quarter 2017 issue of Australian Demographic Statistics (cat. no. 3101.0), with others expected to follow in coming quarters.

Overseas migration

12 For the purposes of NOM, and thereby Australia's official ERP, a person is regarded as a usual resident if they have been (or expect to be) residing in Australia for a period of 12 months or more. This 12-month period does not have to be continuous and is measured over a 16-month period.

13 The ABS introduced the 12/16 month rule for calculating NOM in September quarter 2006. Consequently this point marks a break in series and NOM estimates from earlier periods are not comparable. For further information on the 12/16 month rule see the Technical Note: '12/16 month rule' Methodology for Calculating Net Overseas Migration from September quarter 2006 onwards in Migration, Australia, 2008-09 (cat. no. 3412.0).

14 Preliminary estimates of NOM are required within 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 applied based on changes between intended and actual duration of stay from final NOM estimates one year earlier for travellers with similar characteristics. These characteristics include 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.

15 It is with 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 a traveller's actual duration of stay in or out of Australia to determine inclusion or exclusion from NOM estimates and consequently ERP.

16 In an initiative to create a more efficient and streamlined process for travellers departing Australia, the requirement for international travellers to complete an outgoing passenger card was removed by the Department of Home Affairs from 1 July 2017. Due to the removal of the card the ABS has reviewed its net overseas migration (NOM) statistics, methodology and processing systems. Historical NOM data from September quarter 2011 onwards has been produced based on the new methods and has been used in the 2011-2016 intercensal period as part of the final rebasing of population estimates. As NOM estimates cannot be finalised until 16 months after the reference period, NOM is subject to revision. Testing has shown that the revision between preliminary and final NOM using the new methodology has improved when compared to the previous method. For further information see the Information Paper: Improvements to estimation of net overseas migration, Mar 2018 (cat. no. 3412.0.55.004).

17 Statistics on migration and related data are also published regularly by the Department of Home Affairs <http://www.homeaffairs.gov.au>.


Diplomatic personnel

18 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.


Interstate migration

19 Quarterly interstate migration cannot be directly measured and is estimated using administrative data. To do this the ABS uses information on interstate changes of address from Medicare records (produced by the Department of Human Services) and the Department of Defence in the case of the military.

20 The Medicare-based model is calibrated using migration data from the most recent Census (that data is available for), from which updated expansion factors are calculated. Expansion factors account for undercoverage of Medicare data by age and sex. The current model includes the following characteristics:

• Medicare data is lagged by three months (both for calculating expansion factors and for estimating progressive quarters of interstate migration);
• All single year of age data were smoothed to produce expansion factors;
• capping was applied to expansion factors; and
• expansion factors were applied to males aged 17 to 35 years and females aged 17 to 30 years (this differs to the age range used in the 2006-11 method).

21 The Medicare system theoretically covers all Australian citizens and permanent residents, as well as temporary visa holders. However, some Australian usual residents do not access the Medicare system, such as temporary migrants or those who have access to other health services. One group is the military. Interstate defence force movements not covered by Medicare are estimated and then added to the Medicare-based interstate movement estimates. Quarterly counts of defence force personnel by age, sex and state/territory, supplied by the Department of Defence, form the number of interstate defence force movements, and 70% are assumed to be not covered by the Medicare-based estimates.

22 Preliminary interstate migration estimates for Other Territories are not available. These movements are included in the data for New South Wales (Jervis Bay Territory and Norfolk Island) and Western Australia (Christmas Island and Coco Keeling Islands). Revised interstate migration estimates will become available following the 2021 Census.

23 For further information see Australian Demographic Statistics, December quarter 2017 (cat. no. 3101.0) Technical Note 2: 2016 Census update of the net interstate migration model.


POPULATION PROJECTIONS

24 Population projections presented in this release 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 in the future.

25 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 release, and their assumptions are as follows:

26 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.

27 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.

28 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.


ESTIMATES AND PROJECTIONS OF THE ABORIGINAL AND TORRES STRAIT ISLANDER POPULATION

29 The standard approach to population estimation is not possible for determining the population of Aboriginal and Torres Strait Islander Australians. 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 2016 Census are available in Estimates of Aboriginal and Torres Strait Islander Australians, June 2016 (cat. no. 3238.0.55.001). Projections based on the 2016 Census will be released in 2019 in Estimates and Projections, Aboriginal and Torres Strait Islander Australians (cat. no. 3238.0).

30 Three main projection series were produced for the 2011 Census with assumptions as follows:

31 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.

32 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.

33 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.


HOUSEHOLD PROJECTIONS

34 Household estimates presented in this release are based on the 2016 Census. Household projections based on the 2016 Census will be included in table 16 following the release of Household and Family Projections, Australia, 2016 to 2041 (cat. no. 3236.0) in March 2019.


CONFIDENTIALITY

35 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.

36 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 release, 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

37 In this release, population estimates and their components have sometimes been rounded. Where figures have been rounded, discrepancies may occur between sums of component items and totals.


ACKNOWLEDGMENT

38 ABS statistics 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 REPORTING

39 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.

40 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.


ADDITIONAL STATISTICS AVAILABLE

41 As well as the statistics included in this and related products, 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.