3228.0.55.001 - Population Estimates: Concepts, Sources and Methods, 2009  
ARCHIVED ISSUE Released at 11:30 AM (CANBERRA TIME) 12/06/2009   
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6.1 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 net overseas migration (NOM), and thereby Australia's official estimated resident population (ERP) counts, a person is regarded as a usual resident if they have been (or expected to be) residing in Australia for a period of 12 months or more. As such, NOM and ERP estimates include all people, regardless of nationality or citizenship, who usually live in Australia, with the exception of foreign diplomatic personnel and their families.

6.2 The ABS has developed and introduced an improved method for estimating NOM. It has been used in calculating Australia's official ERP since September quarter 2006. The improved method 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.

6.3 Conceptually the term NOM is based on an international travellers' 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 months does not have to be continuous and is measured over a 16 month reference period. For example 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.

6.4 To be able to accurately measure people that have contributed to NOM estimates there are three main issues for consideration:

  • Is the person in or out of Australia's population prior to the overseas movement?
  • Is the actual duration of stay within (or away from) Australia for at least 12 months?
  • Is the person arriving or departing Australia?

6.5 Estimates of NOM based on the previous methods and those based on the improved methods are not comparable. The key change is the introduction of a '12/16 month rule' for measuring a person's residency in Australia, replacing the previous '12/12 month rule'.

6.6 For further information on the improved methods see Information Paper: Improved Methods for Estimating Net Overseas Migration, 2006 (cat. no. 3107.0.55.003) and Information Paper: Statistical Implications of Improved Methods for Estimating Net Overseas Migration, Australia, 2007 (cat. no. 3107.0.55.005).

6.7 For information on the previous methods 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.

Estimating NOM with 12/16 rule

6.8 The method for estimating NOM was reviewed in 2004 in response to 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.

6.9 The improved NOM estimation methods employ a 12/16 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 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 individuals' actual travel behaviour.

6.10 To measure a travellers actual duration of stay the ABS uses a unique personal identifier provided with the administrative data supplied by the Department of Immigration and Citizenship (DIAC). To be able to apply the 12/16 rule the personal identifier is used to match a travellers movements over time and construct a movement history for each arrival and departure record. For more information on the administrative data used see paragraph 9.62 in Chapter 9 - Data sources.

6.11 At the time preliminary estimates are required (5 to 6 months after the end of the reference quarter), the actual duration of stay in Australia (or overseas) for a traveller in the reference quarter is not known. Hence their contribution to NOM cannot be explicitly determined at this time using the 12/16 rule. Since full movement histories are not available within this timeframe, preliminary NOM estimates are therefore modelled on patterns of traveller behaviours observed in final NOM estimates for the same period two years earlier. More detailed information on preliminary NOM estimation is available later in this chapter.

Travellers vs movements

6.12 Conceptually, NOM estimates should be 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.

6.13 One of the central changes with the improved 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.

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