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TECHNICAL NOTE MEASURING NET OVERSEAS MIGRATION


BACKGROUND

1 Estimates of the Australian population are generated on a quarterly basis by adding natural increase (the excess of births over deaths) and net overseas migration (NOM) occurring during the period to the population at the beginning of each period. This is known as the cohort component method, and can be represented by the following equation:

P_(t+1) = P_(t) + B - D + NOM, where:
P_(t) = the estimated resident population at time point _t
P_(t+1) = the estimated resident population at time point _t+1
B = the number of births occurring between _t and _t+1
D = the number of deaths occurring between _t and _t+1
NOM = net overseas migration occurring between _t and _t+1.

3 Net overseas migration accounts for around half of population growth at the national level. This note outlines how the ABS calculates NOM estimates by state and territory, including adjustments made to overcome some limitations of existing migration data.

4 The ABS estimates the level of NOM occurring during each quarter using data on incoming (i.e. arriving) and outgoing (i.e. departing) passenger movements at Australian air and sea ports. These movements are classified into three main categories depending on the stated duration of stay in Australia or overseas:

• permanent movement
• long-term (one year or more) movement
• short-term (less than one year) movement.

6 Some of these differences between stated travel intentions and actual travel behaviour may also reflect short interruptions to longer periods of stay or absence. For example, overseas students arriving in Australia might state that they intend to stay for three years, but return home for brief periods during this time. Similarly, Australians working or studying overseas might state that they intend to be away for more than a year but return for brief holidays.

7 The following diagram summarises the contributions of different types of overseas movements to NOM. Estimates of NOM are derived from information provided on incoming and outgoing passenger cards, as well as other data supplied by the DIMA. Data on the intended duration of stay of overseas visitors arriving in Australia and the intended duration of absence of Australian residents travelling overseas are used to determine the numbers of permanent and long-term arrivals, and permanent and long-term departures. Passenger card data are also used to calculate migration adjustments and determine the state and territory distribution of NOM.

9 The processes of adjusting movement data on travellers' stated intentions to reflect their actual behaviour are complex, and depend upon the amount and type of movement data available at a particular point in time. The methods currently used compare data on actual travel movements over a one year period with those first advised by individual travellers, and are explained in more detail in Demography Working Paper 2003/5 - Net Overseas Migration: Adjusting for Actual Duration of Stay or Absence (cat.no. 3137.0). In order to conduct such a comparison, data for a 15 month period (i.e. one year plus one quarter) are required. These adjustment methods described in the working paper have been applied to NOM data from the September quarter 2001 onwards and will be subject to further investigation and improvement with the accumulation of additional data and time series.

10 Table 1 describes the impact that various types of migration adjustments have on NOM estimates. The adjustments applied to preliminary and revised NOM estimates are described in more detail elsewhere in this document.

1. MIGRATION ADJUSTMENTS APPLIED TO NOM ESTIMATES
Migration Adjustment		Treatment in adjusted estimates
ADJUSTMENTS MADE TO PRELIMINARY NOM ESTIMATES
Persons whose stated travel intentions differed from assumed travel behavior(a)
	Long-term visitor arrivals assumed to be staying in Australia short-term	Subtract from NOM
	Long-term resident departures assumed to be staying overseas short-term	Add to NOM
	Short-term visitor arrivals assumed to be staying in Australia long-term	Add to NOM
	Short-term resident departures assumed to be staying overseas long-term	Subtract from NOM
ADJUSTMENTS MADE TO REVISED NOM ESTIMATES
Persons whose stated travel intentions differed from actual travel behaviour(b)
	Permanent arrivals who actually stayed in Australia short-term	Subtract from NOM
	Permanent departures who actually stayed overseas short-term	Add to NOM
	Long-term visitor arrivals who actually stayed in Australia short-term	Subtract from NOM
	Long-term resident departures who actually stayed overseas short-term	Add to NOM
	Short-term visitor arrivals who actually stayed in Australia long-term	Add to NOM
	Short-term resident departures who actually stayed overseas long-term	Subtract from NOM
Multiple movements of travellers		Subtract from NOM(c)
(a) Based on trends observed for the proportions of long-term and short-term arrivals and departures who change their travel behaviour.
(b) Based on matched passenger records comparing stated travel intentions with actual behaviour.
(c) Numbers of movements are converted into numbers of persons by matching passport numbers and other identifying personal details.

State and territory distribution of NOM

11 The state and territory distribution of NOM is based on information reported by travellers on arrival in or on departure from Australia. Incoming passenger cards provide information on the state or territory of a traveller's intended address within Australia, while outgoing passenger cards provide information on the state or territory in which a traveller lives or spent most time. However, the way in which this distribution is calculated differs between preliminary and revised estimates of NOM due to the amount of data available.

12 The following sections of this document describe how preliminary and revised estimates of NOM are created and distributed between states and territories. Estimates of NOM are finalised after the five-yearly Census of Population and Housing.

PRELIMINARY NOM ESTIMATES

13 The ABS produces quarterly estimates of Australia's resident population (known as the ERP) five to six months after the end of the reference quarter, and is required under legislation to provide population estimates as at 31 December by early June of the following year. Since estimates of NOM (adjusted for actual travel behaviour) require 15 months of data, preliminary estimates of NOM are calculated to meet more immediate ERP requirements.

Migration adjustments

14 There are four main groups of travellers who provide an intended duration of stay on their passenger cards who have the potential to change their duration of stay or absence:

• long-term overseas visitors who stayed in Australia for less than 12 months (i.e. long-term visitors who stayed in Australia short-term)
• short-term overseas visitors who stayed in Australia for 12 months or more (i.e. short-term visitors who stayed in Australia long-term)
• Australian residents departing long-term who stayed overseas for less than 12 months (long-term departures who stayed overseas short-term)
• Australian residents departing short-term who stayed overseas for 12 months or more (short-term departures who stayed overseas long-term).

2. Changes in travel behaviour(a), Selected categories of movement(b) - September quarter 2003 to June quarter 2004
		LONG-TERM		SHORT-TERM
		Arrivals	Departures	Arrivals	Departures
Period		%	%	%	%
2003
	September	69.9	49.3	2.8	2.8
	December	65.8	48.9	2.3	2.6
2004
	March	70.3	51.7	3.3	3.3
	June	68.6	49.1	2.4	2.3
Average		68.7	49.8	2.7	2.7
(a) Proportion of travellers whose actual duration of stay or absence differed from their stated intentions.
(b) Based on stated intentions

16 An average adjustment based on the most recent complete financial year for which 15 months of data exist is applied to each new quarter of movement data. For example, preliminary NOM estimates for the December quarter 2005 assumed that, based on the 2003-04 evidence, 68.7% of long-term visitor arrivals during the quarter would in fact stay in Australia for less than 12 months, while 49.8% of long-term resident departures would return to Australia within 12 months.

17 Table 3 shows how the preliminary NOM estimate for the December quarter 2005 was calculated.

3. Components of net overseas migration, Original and adjusted estimates - December quarter 2005
		Original estimate	Migration adjustment(a)		Adjusted estimate for preliminary NOM
Initial category of movement		no.	no.	%	no.
Permanent movement
	Permanent (settler) arrivals	33 197	. .	. .	33 197
	Permanent departures	-15 957	. .	. .	-15 957
Long-term movement
	Visitor arrivals	37 830	-25 985	68.7	11 845
	Resident arrivals	33 691	. .	. .	33 691
	Visitor departures	-28 896	. .	. .	-28 896
	Resident departures	-20 509	10 205	49.8	-10 304
Short-term movement
	Visitor arrivals	1 536 408	41 571	2.7	41 571
	Resident arrivals	1 130 298	. .	. .	. .
	Visitor departures	1 426 716	. .	. .	. .
	Resident departures	1 239 302	-34 010	2.7	-34 010
Net overseas migration		39 356	-8 219	. .	31 137
. . not applicable
(a) Refer to table 1 in this document for further information on the migration adjustments applied to preliminary NOM estimates.

State and territory distribution

18 As noted in paragraph 11, the state and territory distribution of NOM is based on information reported by travellers on arrival in or on departure from Australia. However, at the time preliminary NOM estimates are calculated, information on the state or territory in which long-time arrivals will actually spend most time is not available because outgoing passenger cards for these persons have not yet been completed. State and territory distributions of long-term arrivals therefore refer to the state or territory of their intended addresses, as advised on incoming passenger cards. Similarly, state and territory distributions of permanent arrivals refer to their intended addresses as advised on incoming passenger cards, which may differ from the state or territory where they settle in the long-term.

19 The state and territory distribution of preliminary migration adjustments for a particular quarter is assumed to be the same as that of permanent and long-term arrivals in the same quarter. In practice, a national total is calculated for the migration adjustment. This is then distributed across the states and territories, by age and sex, using the distribution of permanent and long-term arrivals by state or territory of intended address. For example, since 23.1% of all permanent and long-term arrivals in the December quarter 2005 intended to live in Victoria, 23.1% of the total migration adjustment (-1,902) is also applied to this state. Table 4 shows components of net overseas migration for December quarter 2005 by state and territory.

4. COMPONENTS OF NET OVERSEAS MIGRATION, States and territories - December quarter 2005
	NSW	Vic.	Qld	SA	WA	Tas.	NT	ACT	Aust.(a)
Category of movement	no.	no.	no.	no.	no.	no.	no.	no.	no.
Permanent and long-term arrivals	40 615	24 227	17 776	5 395	13 100	947	699	1 956	104 718
Permanent and long-term departures	26 587	14 863	11 577	3 045	6 282	608	512	1 878	65 362
Migration adjustment	-3 188	-1 902	-1 395	-423	-1 028	-74	-55	-154	-8 219
Net overseas migration	10 840	7 462	4 804	1 927	5 790	265	132	-76	31 137
(a) Includes Other Territories - see paragraph 2 of the Explanatory Notes.

20 The current method of distributing the preliminary migration adjustment across states and territories is the same as that which has been previously used for preliminary category jumping estimates (see paragraph A3.24 of Demographic Estimates and Projections: Concepts, Sources and Methods (cat. no. 3228.0), available from the ABS web site.

21 However, the ABS plans to review this method, with the prospect of applying a distribution method which allows for positive as well as negative adjustments for individual states and territories. In the interim, the preliminary estimates of NOM are subject to revision when more complete data are available.

REVISED NOM ESTIMATES

22 Preliminary estimates of NOM for a financial year are usually revised in the following March issue of Australian Demographic Statistics (cat. no. 3101.0). These revised NOM estimates use matched passenger records to calculate the actual duration of stay relating to overseas movements. Migration adjustments applied to revised NOM estimates are based on these matched data and include, in addition to the four major movement categories previously identified, a subset of movements relating to permanent arrivals and permanent departures:

• permanent (settler) arrivals who arrived in and left Australia in the same quarter, and did not return at any point during the 12 months following this arrival
• permanent departures who left and returned to Australia in the same quarter, and did not depart at any point during the 12 months following this departure.

24 The current methodology for these revised migration adjustments has been applied from the September quarter 2003 to June quarter 2004. Table 5 shows how revised NOM estimates were calculated for 2003-04.

5. COMPONENTS OF NET OVERSEAS MIGRATION, Original and adjusted estimates - 2003-2004
		Original estimate	Migration adjustment(a)	Adjusted estimate for revised NOM
Initial category of movement		no.	no.	no.
Permanent movement
	Permanent (settler) arrivals	111 589	-7 152	104 437
	Permanent departures	-59 078	3 139	-55 939
Long-term movement
	Visitor arrivals	191 327	-132 384	58 943
	Resident arrivals	98 400	. .	98 400
	Visitor departures	-93 282	. .	-93 282
	Resident departures	-84 336	42 118	-42 218
Short-term movement
	Visitor arrivals	5 057 162	136 710	136 710
	Resident arrivals	3 813 289	. .	3 813 289
	Visitor departures	5 109 267	. .	5 109 267
	Resident departures	3 936 823	-107 085	-107 085
Net overseas migration		164 620	-64 654	99 966
. . not applicable
(a) Refer to table 1 in this document for further information on the migration adjustments applied to revised NOM estimates.

State and territory distribution

25 As is the case for preliminary NOM estimates, the state and territory distribution of revised NOM estimates is determined based on information reported on incoming and outgoing passenger cards (i.e. state or territory of intended address for arrivals and state or territory of residence/spent most time for departures).

26 The state and territory distributions of the migration adjustment are calculated based on the initial passenger card that identifies the movement of the traveller. For example, a long-term resident departure who returned to Australia within twelve months is added back to the state of residence they reported on departure (as identified on their outgoing passenger card). A long-term visitor arrival who actually stayed in Australia for less than twelve months is taken away from the state or territory they intended to live in (as identified on their incoming passenger card).

27 This method may be considered to be reasonable for people who, on arrival, intend to settle or stay in Australia for more than twelve months. However, there is less certainty about the reliability of the state or territory of intended stay for those persons who originally stated that they intended to stay for less than twelve months, but actually stayed longer, and this component of the migration adjustment is treated differently.

28 In the absence of direct information from outgoing passenger cards for this group, the ABS has applied the state and territory distribution for short-term visitors departing Australia who were in Australia for between six and twelve months. The state and territory distributions used for revised NOM estimates (shown in table 6) are still subject to revision. The ABS expects that these estimates will improve as investigations proceed, and as actual data on state or territory of stay becomes available for this segment of the overseas visitor population (i.e. as outgoing passenger cards become available).

6. COMPONENTS OF NET OVERSEAS MIGRATION, States and territories - 2003-04
	NSW	Vic.	Qld	SA	WA	Tas.	NT	ACT	Aust.(a)
Category of movement	no.	no.	no.	no.	no.	no.	no.	no.	no.
Permanent and long-term arrivals	155 162	101 018	67 272	18 025	45 970	3 353	2 755	7 755	401 316
Permanent and long-term departures	98 048	54 285	39 754	10 368	23 433	2 326	1 844	6 614	236 696
Migration adjustment	-27 294	-21 713	-2 119	-3 352	-8 903	-327	-263	-685	-64 654
Net overseas migration	29 820	25 020	25 399	4 305	13 634	700	648	456	99 966
(a) Includes Other Territories - see paragraph 2 of the Explanatory Notes.

CHANGES TO MIGRATION ADJUSTMENT METHODS

29 Due to changes in the methods used to adjust NOM estimates, caution should be used when comparing estimates over time. Table 7 describes the adjustment methods that have been applied to NOM estimates since September quarter 1996 (i.e. since the last intercensal period). Adjustments applied to overseas migration estimates have also been discussed in a special article in Migration, Australia, 2002-03 (cat. no. 3412.0).

7. MIGRATION ADJUSTMENT METHODS - September quarter 1996 to December quarter 2005
Period	Adjustment method
September 1996 - June 1997	Category jumping' adjustments applied using previous methodology(a)
September 1997 - June 2001	No adjustments applied (i.e. 'category jumping' set to zero)
September 2001 - June 2004	Current migration adjustments used (revised NOM estimates)
September 2004 - December 2005	Current migration adjustments methods used (preliminary NOM estimates)
(a) For further information, refer to Appendix 3 in Demographic Estimates and Projections: Concepts, Sources and Methods (cat. no. 3228.0).

FURTHER INFORMATION

30 For further information on the measurement of net overseas migration, contact Phil Browning on Canberra (02) 6252 6639, email <phil.browning@abs.gov.au>.