NET OVERSEAS MIGRATION AND OVERSEAS ARRIVALS AND DEPARTURES
9.61 Comprehensive statistical records on overseas arrivals and departures (OAD) have been maintained since the colonial days. This has been made possible by the relative isolation of Australia, the absence of direct land links with other countries, and the limited number of ports of entry. These natural advantages have been reinforced by government control of arrivals and departures.
9.62 The ABS statistics on overseas migration are calculated using administrative data collected and compiled by the Department of Immigration and Citizenship (DIAC) under the authority of the Migration Regulations (Migration Act 1958). At present, the main source of data on overseas migration is the incoming and outgoing passenger cards completed by all persons arriving in or departing from Australia. Data from passports and visa (entry permit) applications and approvals are also provided by DIAC's Travel and Immigration Processing System (TRIPS). These three data sources (i.e. passenger cards, passports and visa applications) are collected, compiled and matched together by DIAC. Reproduced copies of the current passenger cards are available in Appendix 1 with each issue of Overseas Arrivals and Departures, Australia (cat. no. 3401.0).
9.63 The OAD statistics are sourced from files of monthly extracts of matched TRIPS records provided by DIAC. Statistics on overseas arrivals and departures 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, transit passengers who pass through Australia but are not cleared for entry, passengers on pleasure cruises commencing and finishing in Australia, and unauthorised arrivals. OAD statistics are published on a monthly basis in Overseas Arrivals and Departures, Australia (cat. no. 3401.0).
9.64 Net overseas migration (NOM) quarterly estimates are sourced from the processed OAD data (that has used matched TRIPS data) and monthly extracts of unmatched TRIPS records. These NOM estimates contribute to quarterly ERP and are released in Australian Demographic Statistics (cat. no. 3101.0).
9.65 All migration data sources are subject to non-sampling error which can arise from inaccuracies in collecting, recording and processing the data. The ABS does not have control over any non-sampling error associated with data from DIAC.
9.66 Another dimension of non-sampling error is the fact that the measures of migration estimates become more accurate as more time elapses after the reference period. The trade-off between timeliness and accuracy means that a user can access more accurate data by using the revised or final data.
9.67 The OAD statistics are derived from a combination of full enumeration and sampling of movement records. All permanent movements and all movements with a duration of stay of one year or more are fully enumerated. The number of movements where the duration of stay is less than one year are fully enumerated, however their characteristics are sampled. From January 2005, 4.9% of all short-term movements have been selected for sample. Statistics relating to these movements are therefore weighted estimates.
9.68 As NOM estimates are based on a sample, they are subject to sampling error in addition to non-sampling error as mentioned previously.
9.69 These arise from inaccuracies in collecting, recording and processing the data. Every effort is made to minimise such errors, both through careful design of the passenger cards and through checks on the information once it is received. During the edit process some items are corrected where they conflict with other known information. Missing replies to certain items such as age, state/territory and country of previous residence and main country of intended destination are also imputed by reference to other related items. For further information on non-response rates and data imputation see the Data Quality Issues appendix of Overseas Arrivals and Departures, Australia (cat. no. 3401.0).
9.70 Estimates based on a sample are subject to sampling variability, that is, they may differ from those that would be obtained from full enumeration. One measure of the likely difference resulting from not fully enumerating the OAD collection is provided by the standard error. There are about two chances in three that the sample estimate will differ by less than one standard error from the figure that would have been obtained from full enumeration, and about nineteen chances in twenty that the difference will be less than two standard errors. For further information on standard errors applied to OAD movements see the Standard Errors section of Overseas Arrivals and Departures, Australia (cat. no. 3401.0).
Changes to source data over time
9.71 From July 2001, Department of Immigration and Multicultural and Indigenous Affairs (DIMIA - now DIAC) adopted a new passenger card processing system which involved electronic imaging of passenger cards and intelligent character recognition of the data stored in the images. This process has yielded several improvements to the processing of passenger card data, most notably the detailed information about missing values.
9.72 In July 1998, the Department of Immigration and Multicultural Affairs (DIMA - now DIAC) revised the incoming and outgoing passenger cards and associated procedures as well as computer systems. Following these changes, some questions on the passenger cards were not compulsory and answers to these questions were not checked by Customs officers. The question on marital status was deleted. Data on marital status is now derived from visa applications (only for certain visa classes) and is therefore not available for Australian or New Zealand citizens. The changes also affect the data for 'previous country of residence' which is imputed for Australian and New Zealand citizens. For more information see the May 1998 issue of Overseas Arrivals and Departures, Australia (cat. no. 3401.0). Since July 1998, there have been additional minor changes to both incoming and outgoing passenger cards. Information on age, sex and country of birth is obtained through matching to passport and visa data, while information on time spent in Australia (for visitors and temporary entrants) and time spent abroad (for Australia residents) is calculated through comparison of arrival and departure dates which are accessed through the movements database, maintained by DIAC.
9.73 Early migration statistics were derived from passenger lists (manifests) which masters of ships were required to submit to the authorities on arrival or departure from Australia. Migration statistics were published in varying detail in Statistical Registers or Year Books of the Colonies, and after 1901 also in the Commonwealth Year Book and statistical bulletins.
9.74 With the advent of air travel, people arriving in or departing from Australia lodged a passenger card containing information identical to that previously provided on shipping manifests.
9.75 In 1965, the use of shipping manifests for statistical purposes was abandoned. The control of all passenger movement became the responsibility of the immigration authorities and incoming and outgoing passenger cards were prescribed for use by all sea and air passengers. From January 1974 responsibility for processing passenger cards was transferred from the ABS to DIAC.
9.76 More information on the history of overseas migration statistics is contained in 'Immigration and Ethnicity' (Price 1996) and 'Trans-Tasman Migration: Trends, Causes and Consequences' (Carmichael 1993).