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. NOM estimates are the difference between the number of incoming travellers who are added to the population (overseas migrant arrivals) and the number of outgoing travellers who are subtracted from the population (overseas migrant departures). The number of people counted in NOM is a small fraction of those who travel to or from Australia as most travellers undertake short trips such as holidays. To determine if a traveller is counted as an overseas migrant arrival or departure, the ABS uses the individual’s duration of presence in or out of Australia.

2. Recommendations published by the United Nations define an international migrant as "any person who changes his or her country of usual residence", and also 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, paras 32 & 36).

3. To estimate NOM, and thereby Australia's official estimated resident population (ERP), the ABS employs this concept of usual residence for all travellers who arrive in or depart Australia. A person arriving in Australia is added to the ERP counts if, by arriving in Australia, they are changing their country of usual residence from another country to Australia. The arrival will be counted as an overseas migrant arrival if they reside in Australia for a period of 12 months or more over a 16-month period after arriving. By the same method, a departing person changing their country of residence from Australia to another country is removed from the ERP and counts as an overseas migrant departure. 

4. Measuring the duration of presence in Australia or overseas over a 16-month period means the 12 months does not have to be continuous. For example, a person can leave Australia for a short period after their initial arrival and still be counted as an overseas migrant arrival. For more information see the section on “The 12/16 month rule” below. 

5. NOM and ERP estimates include all people regardless of nationality, citizenship or legal status, who usually live in Australia, except for foreign diplomatic personnel and their families, and are based solely on duration of presence in Australia. 

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.

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 for estimating overseas migration employs the '12/16 month rule'. For the purposes of overseas migration, a person who is not already counted in the estimated resident population (ERP), is added to the ERP if they travel to Australia and remain present in Australia for 12 months or more (i.e. an overseas migrant arrival). Likewise, a person who is already counted in the ERP is removed from the population if they leave Australia for 12 months or more (i.e. an overseas migrant departure). 

2. The 12 months does not have to be continuous and is measured over a 16-month period. The person determined 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.

3. To measure a traveller's actual duration of stay, arrivals and departures are sequenced to construct a traveller's movement history which is then used to measure durations of stay in and out of Australia.  

Preliminary estimates and the propensity model

4. 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 31 March 2023 were modelled on the behaviour of similar travellers from one year earlier. The characteristics used to 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

5. 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 that the ERP status of many individuals can be resolved without the need 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.  

6. 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

7. 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 quarter of 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

8. Preliminary estimates are revised to final NOM estimates once 16 months has passed since the end of the reference period. At this time all required travel data is available for the '12/16 month rule' to be fully applied to all travellers. As such, final NOM estimates are based wholly on actual migration outcomes and replace all previously modelled preliminary estimates.

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.  

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. 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.

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 ABS Consultancy Service via the Consultancy request form.

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 of migration
• 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 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 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 permanent and long-term movements from OAD 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 July 1971, overseas migration estimates were calculated as the total number of overseas arrivals recorded minus the total number of overseas departures recorded. This gave a net total overseas movements count and was used as the migration measure prior to July 1971. 

3. From July 1911 – June 1933, an intercensal adjustment was applied, whereby the latest census count was accepted as the best estimate, and population figures were therefore adjusted to incorporate the discrepancies. Overseas migration was considered the least reliable component of population change at the time and the primary cause of the discrepancy, so the adjustment was applied to overseas departures.

4. From July 1933 – June 1971, the intercensal adjustment was applied to the net migration figure, instead of overseas departures.

5. From July 1971 – June 2006, NOM estimates were based on the number of recorded permanent and long-term overseas arrivals and departures. A number of adjustments were made to these figures from July 1976 onwards.

6. 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. 'Category jumping' was a measure of the discrepancy between movements recorded as short-term, long-term or permanent at the time of movement, and the category recorded at the completion of a journey. In addition, adjustments were also used to transform counts of overseas movements into counts of travellers. Combined, these were referred to as 'migration adjustments'. For more information refer to footnotes (d) and (e) in the ‘Historical methods used for calculating NOM’ table above.

7. 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 migrants on a temporary visa.

8. The ABS noted that using a traveller’s duration of stay to apply a threshold for migration of 12 months in or out of Australia, may lead to incorrect migration outcomes. Frequent travellers may be categorised as short-term, when their overall period of stay or absence was actually long-term but punctuated by short journeys. For example, an international student staying in Australia for a three or four year course of study, may leave Australia briefly each year for a holiday or other reasons. Because they did not spend a continuous period of 12 months in Australia, they would not be added to estimates of Australia's population, when conceptually they should have been. 

9. This would have been inconsistent with the intention behind the United Nations’ definition of overseas (or international) migration (United Nations 1998, 36). 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.

10. Further, there were some travellers who self-identified as permanent arrivals and departures on Australian passenger cards, yet it was observed after less than a year, some permanent arrivals departed Australia and some permanent departures returned to Australia. The ABS also identified that frequent travellers may have multiple border movements recorded within a reference period, and that their travel history could be used to create individual person estimates to avoid double counting.

11. The method for estimating overseas migration was reviewed in 2004 in response to the issues with using the previous method of permanent and long-term arrivals with migration adjustments applied. 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.

12. The '12/16 month rule' method was adopted by the ABS for measuring overseas migration which removed the remaining reliance on traveller-declared intentions as a key element for measuring migration and did so without the use of single continuous periods of stay. This method has been contributing to Australia's ERP since September quarter 2006 and more closely aligns with the intention behind the international definitions set out by the United Nations (United Nations 1998, 36). For further information see "The 12/16 month rule" in the "Processing the data" section above.

13. 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 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. 

14. 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. 

15. 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.

16. 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.