Overseas Migration methodology

This page provides a reference of concepts, sources and methods relating to the collection and processing of overseas migration statistics. Additionally, any changes that may affect statistical quality are also documented on this page. Changes can be due to any part of the end-to-end processing, from administrative passenger data collection to the dissemination of overseas migration statistics. They can range from the design, provision and collection of international passenger movement data through to the administrative systems and updates made by the Australian Government Department of Home Affairs. They can also result from better capture of passenger data, methodological improvements or improved processing systems.

1. Recommendations published by the United Nations define an international migrant as "any person who changes his or her country of usual residence", and state that "the change of country of usual residence necessary to become an international migrant must involve a period of stay in the country of destination of at least a year" (United Nations 1998, 32 & 36). 

2. In Australia, for the purposes of overseas migration (or international migration), a person is added to the population if they have been (or expect to be) residing in Australia for 12 months or more (i.e. an overseas migrant arrival) thus becoming an Australian resident. Likewise, an Australian resident is removed from the population if they leave Australia for 12 months or more (i.e. an overseas migrant departure). The 12 months does not have to be continuous and is measured over a 16-month period. 

3. Conceptually, the term net overseas migration (NOM) is the difference between the number of overseas migrant arrivals and the number of overseas migrant departures.  Therefore, whether an international traveller is counted 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. To identify overseas migrants, all recorded movements of travellers who cross Australia's international border are processed to assess their exact duration of stay.

4. Australia's measurement of overseas migration includes all international travellers regardless of their country of citizenship or legal status, with the exception of foreign diplomatic personnel and their families. 

5. Statistics on overseas migration exclude: all travellers whose duration of stay is less than 12 months; operational air and ships' crew; travellers in transit who pass through Australia but are not cleared for entry; passengers on pleasure cruises commencing and finishing in Australia. From 1 July 2006, foreign diplomatic personnel and their families were also able to be excluded.

1. Administrative information about persons arriving in, or departing from, Australia is collected via various processing systems, passport documents, visa information, and incoming passenger cards (see Passenger card images section). 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 Department of Home Affairs under the authority of the Migration Regulations 1994 made under the Migration Act 1958.

2. ABS statistics on overseas migration are mainly compiled using information from Home Affairs sources. All overseas movement records are stored in Home Affairs' Travel and Immigration Processing System (TRIPS).

3. Each month all overseas arrivals and departures (OAD) movement records and related information, including those matched to an incoming passenger card, are supplied to the ABS and then processed. This OAD data is then the main input to produce quarterly overseas migration estimates. OAD statistics and related data quality issues are published on a monthly basis in Overseas Arrivals and Departures, Australia (cat. no. 3401.0).

4. From July 2017, due to the removal of the outgoing passenger card, the ABS has also used Medicare enrolment data. This is a secondary source of state or territory of residence information for Australian residents and is used for a small proportion of records. For further information see ABS Privacy Impact Assessment Report 'Traveller Information and Medicare Enrolment' released on 12 September 2017. 

5. Statistics in this release draw extensively on information provided by Home Affairs and Medicare. Their continued cooperation is very much appreciated. Without it, the wide range of statistics published by the ABS on overseas migration would not be available. Information received by the ABS is treated in strict confidence as required by the Census and Statistics Act 1905.

The 12/16 month rule

1. The method used in Australia for estimating overseas migration employs the '12/16 month rule'. For the purposes of overseas migration, a person who is not already resident in Australia, is added to the estimated resident population (ERP) if they travel to Australia and remain present in Australia for 12 months or more (i.e. an overseas migrant arrival) thus becoming an Australian resident. Likewise, an Australian resident is removed from the population if they leave Australia for 12 months or more (i.e. an overseas migrant departure). The 12 months does not have to be continuous and is measured over a 16 month period. The person considered to have migrated, is added or removed from the ERP from the date they arrived or departed, i.e. from the beginning of the 16 month calculation period.

2. 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 traveller's movement history recording each arrival and departure. This method is applied for all travellers who cross Australia's international border. 

Preliminary estimates and the propensity model

3. Estimates of overseas migration are required less than six months after the reference quarter for the production of quarterly ERP. At that time, complete traveller histories for the 16 months following a reference quarter are not available. To obtain the required estimates in the absence of complete duration information, preliminary overseas migration estimates are initially modelled using past traveller migration propensities. Due to the disruption to travel patterns during COVID-19, from 1 January 2022 to 31 March 2023 preliminary estimates were modelled on traveller behaviour from the corresponding quarter of 2018. Estimates prior to 1 January 2022 and after the 31 March 2023 were modelled on the behaviour of similar travellers from one year earlier. The characteristics that match similar travellers for preliminary modelling 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 estimates, the migration propensities determined for the donor groupings from one year earlier (or from 2018 where preliminary data was impacted by COVID-19), are applied to similarly grouped travellers from the reference quarter being estimated.

Reducing the pool of travellers that use the propensity model

4. The majority of overseas travellers in a given reference quarter take a trip of short duration. The ERP status of most short-term travellers can be determined based on data available at the time of estimation. This means for many individuals that their ERP status can be resolved without the need for them to be processed through the preliminary propensity model. For example, an Australian resident counted in the ERP at the beginning of a quarter, may commence a holiday during that quarter and then return to Australia two weeks later. Once four months since their return has passed without a further departure, they can be determined to still be in Australia’s population at the end of the reference quarter. This is because, as counted from the date of their original departure, it will no longer be possible for them to be out of Australia for more than 12 months out of 16.  

5. This determination of the ERP status of short-term travellers reduces the proportion of travellers which require modelled estimation to less than 30% of travellers in the quarter. This significantly increases the predictive accuracy of the model. 

Preliminary revised estimates and further reducing the pool of travellers

6. As mentioned above, most short-term travellers can have their ERP status determined based on data available at the time of estimation. However, as more time passes after the initial overseas movement, the ERP status can be determined for more individuals. Therefore, as each new quarters data becomes available the pool of travellers requiring estimation by the propensity model for the original reference period reduces further and a revision is applied to the original preliminary estimation.

Final estimates - applying the 12/16 month rule

7. It is with the final overseas migration estimates that the '12/16 month rule' can be applied to all travellers. Once data on overseas movements become available for the 16 months following a reference period, final overseas migration estimates can then be calculated from the travellers' durations of stay. Final overseas migration estimation methods determine if a traveller, through their actual duration of stay being in or out of Australia for 12 months or more, should be added or removed from the overseas migration estimates, and consequently ERP.

1. The status of quarterly overseas migration estimates changes over time from preliminary, to revised, to final. 

2. Although this publication reports on annual data, the ABS produces estimates each quarter. Overseas migration, at the national level, is one of the three components of population change (birth, deaths and overseas migration). The migration estimates contribute to the ABS' population estimates and are released each quarter in the National, state and territory population publication (cat. no. 3101.0).  

1. The ABS collects statistical information under the authority of the Census and Statistics Act, 1905. This 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.

2. Some techniques used to guard against identification or disclosure of confidential information in statistical tables are suppression of sensitive cells, random adjustments to cells with very small values and rounding. In these cases, data may not sum to totals due to the confidentialisation of individual cells.

3. The statistics in this release have been rounded to the nearest 10 to maintain confidentiality. Where figures have been rounded, discrepancies may occur between sums of component items and totals. All calculations and analysis are based on un-rounded data. Calculations made on rounded data may differ to those published.

4. To minimise risk of identifying individuals in aggregate statistics, perturbation is sometimes used to randomly adjust cell values available via services such as Table Builder. This technique involves small random adjustments of the data 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 patterns. After perturbation, a given cell value will be consistent across all tables. Where figures have been perturbed, discrepancies may occur between sums of component items and totals.

1. The ABS may have other relevant data available on request. Generally, a charge is made for providing this information. Enquiries should be made to the National Information and Referral Service on 1300 135 070.

2. The following variables for overseas migration data may be made available on request:

• Age
• Country of birth
• Country of citizenship
• Country of previous residence
• Direction
• Category of travel (permanent departures not available from Sep quarter 2011)
• Main reason for journey (not available for permanent movements, residents departing or visitors departing)
• Marital status (not available from Sep quarter 2011 or for Australian and New Zealand citizens)
• Reference quarter/year (available from Dec quarter 2003)
• Sex
• State or territory of residence
• Status (preliminary, revised or final)
• Visa applicant type (primary or secondary applicant - available from Sep quarter 2011)
• Visa subclass (includes separate groups for Australian citizens and NZ citizens)

1. The classification of countries used in this release is the ABS' Standard Australian Classification of Countries 2016. The entire historical series has been backcast using this version of the classification.

2. The statistics on country of residence or main destination have certain limitations as they rely on self-reported information collected on incoming passenger cards. For example, many travellers just list the UK on their passenger card rather than stating England, Scotland, Wales, or Northern Ireland.

3. Overseas arrivals and departures data covers Australia and its states and territories, as defined by the Australian Statistical Geography Standard (ASGS), Edition 3. Jervis Bay Territory, the Territories of Christmas Island, Cocos (Keeling) Islands and Norfolk Island are included as one spatial unit at the State and Territory level under the category of Other Territories. 

Historical changes to the State and Territory classification

4. Following the 1992 amendment to the Acts Interpretation Act, the Indian Ocean Territories of Christmas Island and the Cocos (Keeling) Islands were included as part of geographic Australia. To reflect this change, another category was created, known as Other Territories which also included Jervis Bay Territory (previously included with the Australian Capital Territory). Overseas arrivals and departures data for Other Territories commenced from February 1995.
            
5. Norfolk Island was included in the Other Territories category from July 2016 following the introduction of the Norfolk Island Legislation Amendment Act 2015. Prior to this, Norfolk Island was an external territory and not included within geographic Australia.

1. Due to changes in the methods used to measure overseas migration estimates, caution should be used comparing them over time. This is especially so for estimates based on the '12/12 month rule' method compared to those using the '12/16 month rule' method. The table below describes the various methods used in Australia that have been applied to measuring overseas migration.

2. Prior to 1 July 2006, overseas migration estimation methods used a '12/12 month rule' to determine if a traveller contributed to Australia's estimated resident population (ERP). For a person to have immigrated or emigrated, they must have stayed in, or were absent from, Australia for a continuous period of 12 out of 12 months. 

3. Conceptually, migration 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. Prior to July 2006 a number of adjustments to overseas arrivals and departures were required. These mainly comprised adjustments designed to reflect differences between an individual's stated travel intentions (from the passenger card) and their actual recorded travel behaviour. If they changed from a long-term to a short-term traveller and vice versa it was referred to as 'category jumping'. In addition, adjustments were also required to transform numbers of overseas movements into numbers of travellers (combined they were referred to as 'migration adjustments'). For more information refer to footnotes (d) and (e) in the table above.  

4. During a reconciliation of the 1996-2001 intercensal population growth estimates with the results of the 2001 Census of Population and Housing, the ABS identified a number of inconsistent results for the overseas migration estimates. These inconsistencies arose from a 1998 passenger card processing change and the measurement of temporary migration.

5. The ABS noted that the precise measurement of duration of stay in Australia (or absence) 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 '12/12 month rule' method of measurement). This was inconsistent with the intention behind the definition of an overseas (or international) migrant by the United Nations (United Nations 1998, 36) and the ABS' ERP conceptual definition. The use of single continuous periods of stay as the criteria (i.e. 12 continuous months) for classifying travellers was seen as a major shortcoming in the measurement of migration and consequently estimates of Australia's resident population.

6. Further, there were some travellers who self-identified as permanent immigrants and emigrants on Australian passenger cards, yet it was observed after 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.

7. The method for estimating overseas migration was reviewed in 2004 in response to the issues arising with the previous estimation of category jumping (i.e. changes between stated intended duration and actual duration). The review also addressed the changing patterns of migration, in particular the increased propensity for travellers to interrupt longer periods of stay or absence with short-term trips.

8. The change to a '12/16 month rule' method was adopted by the ABS for measuring overseas migration and has been contributing to Australia's ERP since September quarter 2006. It more closely aligns with the intention behind the international definitions set out by the United Nations (United Nations 1998, 36). The ABS has not changed the statistical conceptual definition of overseas migration. However, the method of measurement changed.

9. In an initiative to create a more efficient and streamlined process for travellers departing Australia, the outgoing passenger card was removed by Home Affairs from 1 July 2017. Due to the removal of the card, the ABS reviewed its overseas migration methodology and processing systems. From this review the most significant changes were:

• The inclusion of an additional month of movement data (allowing four months after the reference period) — this further reduced the pool of travellers required to use the propensity model, improving the accuracy of preliminary migration estimation; 
• Changes in data sources for state/territory of residence — data previously sourced from the outgoing passenger card is now collected from an incoming passenger card for that traveller or information from Medicare enrolment records for Australian residents;
• Incorporating improvements to the personal identifier (known as PID) for movement records — a consistent PID for each traveller is crucial for determining a traveller's actual duration in or out of the country. Updated PID data is supplied by Home Affairs each month and used to improve the quality of travel histories that are produced for each traveller. 

10. Historical estimates from September quarter 2011 onwards were revised using the new methods. Analysis had shown that the revision between preliminary and final estimates, using the new methodology, had also improved when compared to the previous method. For more information refer to footnote (k) in the table above. 

11. For detailed information on the 2017 changes to the main input data, overseas arrivals and departures data, including imputation, secondary sources used and information on the state/territory of residence, see History of changes in Overseas Arrivals and Departures, Australia, methodology (cat. no. 3401.0).

12. Due to the disruption to travel patterns during COVID-19, from 1 January 2022 to 31 March 2023 preliminary estimates were modelled on traveller behaviour from the corresponding quarter of 2018. Estimates prior to 1 January 2022 and after the 31 March 2023 were modelled on the behaviour of similar travellers from one year earlier.