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10 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 OVERSEAS MIGRATION (NOM)
11 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 NOM, and thereby Australia's official ERP counts, 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 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.
12 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.
Source of overseas migration data
13 Administrative information on persons arriving in, or departing from, Australia is collected via various processing systems, passport documents, visa information, and incoming passenger cards. Aside from persons travelling as Australian or New Zealand citizens, persons travelling to Australia are required to provide information in visa applications. These administrative data are collected by the Australian Government Department of Home Affairs (Home Affairs) under the authority of the Migration Regulations 1994 made under the Migration Act 1958.
14 ABS statistics on overseas migration are mainly compiled using information from Home Affairs sources. All overseas movement records are stored on Home Affairs' Travel and Immigration Processing System (TRIPS). Each month all movement records, including those matched to an incoming passenger card, are supplied to the ABS and then processed. From July 2017, due to the removal of the outgoing passenger card, the ABS has also used Medicare enrolment data as a secondary source of State of residence information for Australian residents.
15 Each month all overseas arrivals and departures (OAD) movement records are processed by the ABS to produce OAD statistics. This processed OAD data is then used to produce quarterly NOM estimates. Statistics on OAD and related data quality issues are published on a monthly basis in Overseas Arrivals and Departures, Australia (cat. no. 3401.0). Quarterly NOM estimates contribute to quarterly ERP and are released in Australian Demographic Statistics (cat. no. 3101.0).
16 Statistics on overseas migration exclude: multiple movements; the movements of operational air and ships' crew; transit passengers who pass through Australia but are not cleared for entry; passengers on pleasure cruises commencing and finishing in Australia and undocumented arrivals. From 1 July 2006 onwards, foreign diplomatic personnel and their families are also excluded.
Reasons for change of methods used to estimate NOM
17 During a reconciliation of 1996-2001 intercensal population growth estimates (including measures of immigration, emigration and NOM) with the results of the 2001 Census of Population and Housing, the ABS identified that inconsistent results were arising from a 1998 passenger card processing change and the measurement of temporary visitors' duration of stay in Australia, or Australian residents' temporary duration of absence from Australia.
18 The ABS noted that the precise measurement of duration of stay in Australia or absence from Australia using a comparison of border crossing transactions may lead to a misleading categorisation of frequent travellers to short-term, when their overall period of stay or absence in a broader context was long-term punctuated by short journeys. For example, an international student in Australia for a three or four year course of study, who leaves Australia briefly each year for holiday or other reasons, would incorrectly not be added to estimates of Australia's population. This was because after the passage of time, they did not spend a continuous period of 12 months in Australia during their long-term period of stay in Australia (the previous method of measurement). This was inconsistent with the intention behind the definition of a long-term migrant as set out in the United Nations Recommendations on Statistics of International Migration, Revision 1 (1998, 18) and the ABS Estimated Resident Population conceptual definition. The use of single continuous periods of stay as the criteria (i.e. 12 continuous months) for classifying travellers into the non-permanent migration categories (e.g. short-term visitor, long-term visitor) was seen as a major shortcoming in the measurement of NOM and consequently estimates of Australia's resident population.
19 Further, there were some travellers such as permanent immigrants and emigrants who were not asked their intended duration of stay or absence on Australian passenger cards, yet it was observed that after a passage of less than a year, some permanent immigrants departed Australia and some permanent emigrants returned to Australia. The ABS also identified a need to convert the multiple border movements information for frequent travellers within a reference period to individual person estimates together with their travel history over time to avoid double counting.
20 The method for estimating NOM was reviewed in 2004 in response to the issues arising with the previous estimation of category jumping (i.e. changes between stated intention and actual duration of stay of travellers to/from Australia). The review also addressed the changing patterns of travel into and out of Australia, in particular the increased propensity for travellers to interrupt longer periods of stay or absence with short-term trips.
21 The methodology and estimation system adopted by the ABS for measuring NOM and the contribution to Australia's ERP more closely aligns with the international definitions set out by the United Nations. The ABS has not changed the statistical conceptual definition of net overseas migration. However, the method of measurement has changed.
22 The ABS developed and introduced an improved method, called the '12/16 month rule' methodology, for estimating NOM. It has been used in calculating Australia's official ERP since September quarter 2006. The '12/16 month rule' methodology is a result of 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.
23 Estimates of NOM based on the previous methods and those based on the '12/16 month rule' methodology are not comparable. The key change is the introduction of the '12/16 month rule' for measuring a person's residency in Australia, replacing the previous '12/12 month rule'.
24 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).
25 For further information on the improvements to NOM estimation over time and changes to the revision schedule for NOM, see:
26 For further information on the '12/16 month rule' methodology see:
Estimating NOM with the '12/16 month rule' (current method used)
27 The current NOM estimation methods employ the '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 (or models this behaviour for preliminary NOM).
28 To measure a traveller's actual duration of stay the ABS uses a unique personal identifier provided with the administrative data supplied by Home Affairs. To be able to apply the '12/16 month rule', the personal identifier is used to match a traveller's movements over time and construct a movement history for each arrival and departure record.
Travellers vs movements
29 Conceptually, NOM estimates are based on counts of travellers, rather than counts of overseas movements, since travellers may have more than one movement in a particular reference period. Under the previous system of NOM estimation, a number of adjustments to overseas arrivals and departures were required. These mainly comprised adjustments designed to reflect differences between stated travel intentions and actual travel behaviour. However, adjustments were also required to transform numbers of overseas movements into numbers of travellers.
30 One of the central changes with the '12/16 month rule' methodology is that all estimation is based on actual individual travellers and their travel histories (using de-identified data), rather than in the previous methodology when an aggregation of movements represented travellers.
Final NOM estimates
31 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
32 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. To estimate preliminary NOM, the ABS uses a propensity model that estimates a traveller's propensity to contribute to NOM using the observed behaviour of similar travellers from one year earlier. Travellers with similar characteristics are grouped according to specific variables. The variables used are: age, country of citizenship, direction of first and last movement in the reference quarter, initial ERP status, time spent out of Australia, and visa group. To create the preliminary NOM estimates, the migration propensities determined for the donor groupings from one year earlier are applied to similarly grouped travellers from the reference quarter being estimated.
33 In 2017, the removal of the outgoing passenger card by Home Affairs resulted in further changes in the data and methods used in the calculation of NOM. Of these changes, those most significant are:
34 For detailed information on the 2017 changes in OAD data including imputation, secondary sources used, and in particular information on the state/territory of residence, see Data Quality Issues (Appendix) under the Explanatory Notes tab in Overseas Arrivals and Departures, Australia (cat. no. 3401.0).
35 Preliminary estimates using the new method for estimating NOM after the removal of the outgoing passenger card were implemented in the ABS' official NOM and population estimates for September quarter 2011 onwards with the release of the December quarter 2017 issue of Australian Demographic Statistics (cat. no. 3101.0). For further information on the new method see the Information Paper: Improvements to estimation of net overseas migration, Mar 2018 (cat. no. 3412.0.55.004).
Estimating NOM with a '12/12 month rule' (previous method used)
36 Prior to 1 July 2006, NOM estimation methods used a '12/12 month 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 information see the Technical Note in Migration, Australia, 2006-07 (cat. no. 3412.0) - Measuring Net Overseas Migration, Method Used September quarter 2001 to June quarter 2006 and Demography Working Paper 2003/5 - Net Overseas Migration: Adjusting for Actual Duration of Stay or Absence (cat. no. 3137.0).
Methods used for estimating Net Overseas Migration and revision status
37 Due to changes in the methods used to adjust NOM estimates, caution should be used comparing estimates over time. The table below describes the adjustment methods that have been applied to NOM estimates from September quarter 1996 onwards.
REGIONAL OVERSEAS MIGRATION
38 Regional overseas migration estimates (ROME) break annual state and territory-level overseas migration arrivals and departures into sub-state areas, using information from the most recent Census, with up-to-date visa and overseas student data taken into account. Since 2016-17, ROME has been used in the compilation of 30 June sub-state ERP. ROME is released in Regional Population Growth, Australia (cat. no. 3218.0), and more information on the method to prepare ROME is provided in this product.
PERMANENT RESIDENCY GRANTS
39 A number of people arriving temporarily in Australia are subsequently granted permanent residency. These permanent residency grants contribute to the Australian Government's immigration targets but may be unrelated to the stated intentions of travellers on arrival. Accordingly, they are not included in unadjusted permanent arrivals as they did not arrive in Australia on a permanent basis but would be included in final NOM figures from 1 July 2006 onwards (if satisfying the "12/16 month rule"). The proportions of temporary arrivals subsequently gaining onshore grants of permanent residency are not estimated in ABS statistics.
40 For more information on onshore additions to the population see the Home Affairs publication, Immigration Update, or Population Flow: Immigration aspects available on the Home Affairs web site, http://www.homeaffairs.gov.au.
OVERSEAS ARRIVALS AND DEPARTURES (OAD) STATISTICS
41 The ABS statistics on overseas arrivals and departures (OAD) are calculated using administrative data collected and compiled by Home Affairs under the authority of the Migration Regulations (Migration Act, 1958). The monthly OAD publication contains statistics on the travel movements of all persons arriving in, and departing from, Australia. Its main focus is to provide information and analysis of short-term movements (i.e. less than one year), in particular short-term visitor arrivals (STVA) and short-term resident returns (STRR). Statistics on overseas arrivals and departures relate to the number of movements of travellers rather than the number of travellers. Individuals who travel multiple times in a year are counted each time they cross Australia's borders. Permanent and long-term movements from OAD statistics are not an appropriate source of migration statistics.
The 2017 review and break in series
42 From 1 July 2017, travellers leaving Australia are no longer required to complete an Outgoing Passenger Card (OPC). Due to the removal of the OPC by the Department of Home Affairs, the ABS undertook a review of its Overseas Arrivals and Departures (OAD) statistics, methodology and processing systems. This provided an opportunity to consider alternative data sources and ways to make better use of a range of existing data collected by Home Affairs about Australia's international border crossings. Detailed information on the changes and improvements arising from the 2017 review of OAD statistics appears in the Data Quality Issues (Data Quality Issues Appendix) in the Explanatory Notes section in Overseas Arrivals and Departures, Australia (cat. no. 3401.0).
43 The review has resulted in a break in series, necessitating a revised time series for OAD data from July 2007 to June 2017 based on the new methodology. Figures prior to June 2007 may not be strictly comparable to those which follow.
44 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 undocumented arrivals or departures.
NET INTERSTATE MIGRATION
45 At the national level, population change is the result of births, deaths and net overseas migration. At the state/territory level, an extra component of population change exists - net interstate migration. This is the net difference between arrivals to a state/territory from the rest of Australia and departures from that state/territory to the rest of Australia. Interstate migration is therefore an important determinant of population change and distribution of the states and territories.
46 Within Australia, there is no requirement for a person who changes their state of usual residence to register their move. Unlike overseas movements, which are recorded at Australia's borders, there are no direct quarterly measure of arrivals and departures between the states and territories. To be able to measure state/territory population change on a quarterly basis estimates of interstate migration are therefore required.
Sources of interstate migration data
47 The Census is one source of information, with people being asked where they lived one year ago and five years ago. However, as the Census is held only every five years, this is insufficient for producing quarterly interstate migration estimates. Another source of data is therefore necessary.
48 Interstate migration is a key determinant of the accuracy of state and territory population estimates. Data on interstate migration cannot be directly estimated unlike that of natural increase and net overseas migration. Instead, post-censal quarterly estimates of interstate migration are modelled using administrative by-product data. Over time, the ABS has used a number of administrative data sources to produce quarterly estimates of interstate migration, including electoral roll registrations and family allowance payments. Currently the ABS uses information on interstate change of address advised to Medicare Australia and to the Department of Defence in the case of the military.
49 Due to incomplete coverage and the non-compulsory nature of available administrative (indirect) data sources, 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.
Rebasing and re-derivation of interstate migration
50 The Medicare-based model used for generating post-censal estimates of interstate migration is largely superseded when new Census information becomes available. For example, every five years, after data from the following Census have been finalised, the modelled estimates are reviewed against, and potentially replaced by, the interstate migration estimates that are calculated from the Census (i.e. rebased to the Census). This is known as the re-derivation of interstate migration.
51 Part of the process of rebasing Census counts for the ERP of the states and territories is the re-derivation of interstate migration for the intercensal period. The overall approach is to minimise state intercensal difference using information from the two Census questions on usual residence one year ago and five years ago to estimate interstate movements. Where this Census information does not reduce the intercensal difference, the rebased interstate migration estimates remain largely unchanged from the Medicare-based model.
Interstate migration method
52 Post-censal quarterly estimates of net interstate migration are created for the states and territories (excluding Other Territories) using interstate change of address advised to Medicare Australia and to the Department of Defence in the case of the military. Medicare data are adjusted by means of expansion factors. These expansion factors are used to account for an under coverage of Medicare data by various ages and sex. For example, it is known that some people, particularly younger Medicare card holders, do not register changes of address with Medicare, or do so long after the fact.
53 Expansion factors are used in the calculation of post-censal quarterly estimates of net interstate migration and remain constant throughout the intercensal period until once again they are reviewed after final data from the following Census becomes available. They are calculated for each state and territory (excluding Other Territories), single year of age, sex and movement direction (i.e. arrivals or departures). For further information see Technical Note 2, 2016 Census Update of the Net Interstate Migration Model in Australian Demographic Statistics, Dec 2017 (cat. no. 3101.0).
54 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 Technical Note 2, 2016 Census Update of the Net Interstate Migration Model in Australian Demographic Statistics, Dec 2017 (cat. no. 3101.0).
55 For further information on the process of estimating interstate migration and the administrative data used, see
REGIONAL INTERNAL MIGRATION
56 Regional internal migration is the movement of people from one area to another within Australia, both interstate and intrastate. Annual regional internal migration estimates (RIME) have been used in the compilation of 30 June sub-state ERP since 2016-17. RIME is prepared from aggregated annual Medicare change of address data, coded directly to ASGS areas, supplemented by aggregated defence force personnel movements. Since 2016-17, RIME has been released in Regional Population Growth, Australia (cat. no 3218.0).
57 RIME was released in Migration, Australia (cat. no. 3412.0) for years up to 2015-16. Users should be cautious when comparing pre-2016 RIME with the current RIME series, due to a change in methodology. The pre-2016 RIME series was prepared using quarterly postcode-based Medicare change of address data (meaning that a person could record up to four moves in a year), and was then converted to ASGS areas. The current RIME series allocates moves directly to ASGS areas, on an annual basis.
58 The classification of countries in this release is the Standard Australian Classification of Countries, 2016. For more detailed information, refer to the ABS publication Standard Australian Classification of Countries (SACC) 2016 (cat. no. 1269.0) or the Country Classification excel spreadsheet in the Downloads tab of this release.
59 The statistics on country of residence or main destination, and country of embarkation have certain limitations because of reporting on passenger cards. For instance, the United Kingdom, Channel Islands and Isle of Man (UK, CI & IOM) includes England, Scotland, Wales, Northern Ireland, Guernsey, Jersey and the Isle of Man. Many travellers just list the UK. Similarly the United States of America includes 'America (undefined)'.
STATE AND TERRITORY CLASSIFICATION
60 Prior to the 1996 Census, no external territories were included in geographical Australia although Census data were collected for Christmas Island and the Cocos (Keeling) Islands. Following amendments to the Acts Interpretation Act 1901 effective from July 1992, the two external territories of Christmas Island and Cocos (Keeling) Islands became part of geographical Australia. Since the 1996 Census, Christmas Island, Cocos (Keeling) Islands, and the Jervis Bay Territory (previously linked to the Australian Capital Territory for statistical purposes) have been grouped under 'Other Territories'. 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.
61 Although the Census and Statistics Act 1905 does not require quarterly estimation of the population for the territories, estimates for the Northern Territory, the Australian Capital Territory and the Other Territories are produced as these territories are included in the geographical area of Australia, and, with the states, sum to the Australian population.
62 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.
63 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.
64 To minimise the risk of identifying individuals in aggregate statistics, a technique is used to randomly adjust cell values. This technique is called perturbation. Perturbation involves small random adjustment of the statistics and is considered the most satisfactory technique for avoiding the release of identifiable statistics while maximising the range of information that can be released. These adjustments have a negligible impact on the underlying pattern of the statistics. After perturbation, a given published cell value will be consistent across all tables. However, adding up cell values to derive a total will not necessarily give the same result as published totals. The introduction of perturbation in publications ensures that these statistics are consistent with statistics released via services such as Table Builder.
65 In this release, estimates and their components have sometimes been rounded. Rounded figures and un-rounded 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
66 Additional information is available on the ABS web site https://www.abs.gov.au.
67 The ABS may have other relevant data available on request. Generally, a charge is made for providing this information. Inquiries should be made to the National Information and Referral Service on 1300 135 070.
68 With the introduction of '12/16 month rule' methodology for estimating NOM, the ABS also developed an analytical data set called the Travellers' Characteristics Database. The improvements allow the derivation of an individual's actual true travel behaviour (using final NOM data) and record certain characteristics for any traveller who has contributed to NOM whether they are a NOM arrival or a NOM departure. The database provides for additional analysis on final NOM data. The following variables may be made available on request for final data only:
69 This publication draws extensively on information provided by Home Affairs, Medicare and the Department of Defence. The ABS also uses 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 by 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.
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