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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.

2 For state and territory population estimates, an additional term is added to the equation representing net interstate 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.

Migration adjustments

8 The ABS applies a number of adjustments to overseas arrivals and departures data in order to produce estimates of NOM. These mainly comprise adjustments designed to reflect differences between stated travel intentions and actual travel behaviour, but (in the case of revised NOM estimates) also include adjustments to transform numbers of overseas movements into numbers of travellers. Until recently, adjustments used by ABS to produce NOM estimates were collectively referred to as 'category jumping adjustments'. They are now referred to more simply as 'migration adjustments'.

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 (<https://www.abs.gov.au>, select Themes> Demography > ABS Demography Working Papers). In order to conduct such a comparison, data for a 15month 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 below 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.

Migration Adjustment	Treatment in adjusted estimates
ADJUSTMENTS MADE TO PRELIMINARY NOM ESTIMATES
Persons whose stated travel intentions differed from actual 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)

State and territory distribution of NOM

11 The state or 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).

	LONG-TERM			SHORT-TERM
	Arrivals	Departures		Arrivals	Departures
Period
	%	%		%	%
2001
September	70.6	49.2		4.1	3.7
December	69.3	47.8		3.6	3.7
2002
March	71.3	52.3		4.1	4.1
June	69.0	48.7		3.5	3.2
Average	70.0	49.5		3.8	3.7

	ORIGINAL ESTIMATE		MIGRATION ADJUSTMENT(a)			ADJUSTED ESTIMATE FOR PRELIMINARY NOM
Initial category of movement
	no.		no.	%		no.
Permanent movement
Permanent (settler) arrivals	28,689		..	..		28,689
Permanent departures	-14,012		..	..		-14,012
Long-term movement
Visitor arrivals	49,876		-34,934	70.0		14,942
Resident arrivals	23,125		..	..		23,125
Visitor departures	-20,278		..	..		-20,278
Resident departures	-20,022		9,908	49.5		-10,114
Short-term movement
Visitor arrivals	1,163,359		44,376	3.8		44,376
Resident arrivals	909,028		..	..		..
Visitor departures	1,141,142		..	..		..
Resident departures	947,696		-34,603	3.7		-34,603
Net overseas migration	47,377		-15,253	..		32,124

State and territory distribution

18 As noted above at paragraph 10, the state or 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 in 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 longer 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 24.8% of all permanent and long-term arrivals in the September quarter 2003 intended to live in Victoria, 24.8% of the total migration adjustment (-3,783) is also applied to this state. Table 4 shows components of net overseas migration for September quarter 2003 by state and territory.

Category of movement	NSW	Vic.	Qld	SA	WA	Tas.	NT	ACT	Aust.(a)
Permanent and long-term arrivals	39,802	25,221	17,078	4,343	11,759	751	776	1,957	101,689
Permanent and long-term departures	23,307	11,703	9,070	2,369	5,217	498	441	1,699	54,312
Migration adjustment	-5,970	-3,783	-2,562	-651	-1,764	-113	-116	-294	-15,253
Net overseas migration	10,525	9,735	5,446	1,323	4,778	140	219	-36	32,124
(a) Includes Other Territories - see paragraph 2 of the Explanatory Notes.

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 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.

	Original estimate	Migration adjustment(a)	Adjusted estimate for revised NOM
Initial category of movement
Permanent movement
Permanent (settler) arrivals	88,900	-4,487	84,413
Permanent departures	-48,241	2,382	-45,859
Long-term movement
Visitor arrivals	175,873	-128,059	47,814
Resident arrivals	88,598	..	88,598
Visitor departures	-79,375	..	-79,375
Resident departures	-92,071	46,942	-45,129
Short-term movement
Visitor arrivals	4,768,294	182,494	182,494
Resident arrivals	3,344,976	..	..
Visitor departures	4,837,761	..	..
Resident departures	3,367,870	-122,400	-122,400
Net overseas migration	133,684	-23,128	110,556
.. not applicable (a) Refer to Table 1 in this document for further information on the migration adjustments applied to revised NOM estimates.

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).

Category of movement	NSW	Vic.	Qld	SA	WA	Tas	NT	ACT	Aust.(a)
Permanent and long-term arrivals	144,441	83,181	60,711	13,781	38,645	2,731	2,597	7,256	353,371
Permanent and long-term departures	93,101	48,932	35,845	9,300	21,338	2,249	2,453	6,419	219,687
Migration adjustment	-6,929	-13,997	1,622	-1,683	-2,337	-175	511	-139	-23,128
Net overseas migration	44,411	20,252	26,488	2,798	14,970	307	655	698	110,556
(a) Includes Other Territories — see paragraph 2 of the Explanatory Notes.

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 will also be discussed in a special article in Migration, Australia, 2002-03 (cat.no.3412.0), scheduled for release on 28 April 2004.

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 2002	Current migration adjustments methods used (revised NOM estimates)
September 2002 - September 2003	Current migration adjustments methods used (preliminary NOM estimates)(b)
(a) For further information, refer to Appendix 3 in Demographic Estimates and Projections: Concepts, Sources and Methods (cat. no. 3228.0).
(b) Estimates for the 2002-03 financial year will be revised in the March 2003 issue of Australian Demographic Statistics (cat. no. 3101.0), scheduled for release in September 2004.

30 For further information on the measurement of net overseas migration, contact Rhonda de Vos on Canberra (02) 6252 6639, email rhonda.devos@abs.gov.au.