Historical population methodology

1 Australian Historical Population Statistics is a compendium electronic release which contains a wide range of historical demographic data on a variety of topics. The data are presented in spreadsheet format (Microsoft Excel) going back, where possible, to European colonisation of Australia in 1788.

2 This product is updated periodically. Since the 2014 edition, Local Government Area (LGA) populations for the years 1961, 1986 and 2011 (tables 3.6 - 3.8) have been replaced with the years 1954, 1976, 1996 and 2016 (tables 3.6 - 3.9).

3 More up-to-date information may be available from the source products stated at the bottom of each spreadsheet. A list of related Australian Bureau of Statistics (ABS) and other publications can also be found below.

4 Where original sources are referred to:

• (original source) as quoted in Australian Bureau of Statistics, (year), Australian Historical Population Statistics (cat. no. 3105.0.65.001).
   

If reference is desired only to Australian Historical Population Statistics:

• Source: Australian Bureau of Statistics, (year), Australian Historical Population Statistics (cat. no. 3105.0.65.001).
   

5 Australian Historical Population Statistics data have been compiled from a wide range of sources, including:

• Colonial censuses, State censuses, Colonial Statistical Returns and Colonial Statistical Registers;
• Australian Demography Bulletins produced by the Commonwealth Bureau of Census and Statistics;
• Commonwealth censuses;
• ABS demography publications; and
• other ABS demography collections.

6 A summary of 19th century statistics collected by the colonial statistical bureaux can be found in the ABS publication Catalogue of Australian Statistical Publications, 1804 to 1901(cat. no. 1115.0).

7 Early estimates of the Australian Aboriginal and Torres Strait Islander population have been compiled from The Aboriginal Population of Australia (1980) by L.R. Smith, Australian National University Press for the Academy of Social Sciences in Australia, Canberra (1980). More recent estimates have been compiled from the Census of Population and Housing and other ABS demography collections.

8 Given that different sources often exist for the same data, minor discrepancies may exist between Australian Historical Population Statistics and these sources. References to the sources of information used to compile these statistics are given at the bottom of each spreadsheet.

9 The terms 'state' and 'territory' are used to describe states and territories as they exist in the post-Federation period, as well as the various colonies that existed prior to Federation. For example, data presented in the tables under the heading 'NSW' relates to both the colony of New South Wales and the state of New South Wales.

10 Tasmania, Victoria and Queensland became independent from New South Wales in the years 1825, 1851 and 1859 respectively. Western Australia and South Australia came into existence in 1829 and 1836 respectively.

11 The Northern Territory and the Australian Capital Territory (ACT) came under the control of the Federal Government in 1911 and were no longer included in the estimates for South Australia and New South Wales respectively. Although the Northern Territory ceased to exist briefly between 1 February 1927 and 11 June 1931, being replaced by the territories of North Australia and Central Australia, for purposes of comparison, the figures for combined North Australia and Central Australia are described as "Northern Territory" in Table 3.2 for the periods 1927-1931.

12 Following the 1992 amendments to the Acts Interpretation Act to include the Indian Ocean Territories of Christmas Island and the Cocos (Keeling) Islands as part of geographic Australia, population estimates commencing from September quarter 1993 include estimates for these two territories. To reflect this change, another category at the state and territory level has been created, known as Other Territories. Other Territories include Jervis Bay Territory (included in ACT estimates from 1915 to June quarter 1993), as well as Christmas Island and the Cocos (Keeling) Islands which were previously excluded from population estimates for Australia. From 1 July 2016, 'Other Territories' also include Norfolk Island following the introduction of the Norfolk Island Legislation Amendment Act 2015.

13 In this publication, the term population refers to the counts of people in Australia, regardless of the method of enumeration from 1788 to the present day. Australian Historical Population Statistics uses four measures of population: actual location Census counts, usual residence Census counts, population estimates, and the estimated resident population (ERP).

14 Actual location Census counts are counts of all people, within the scope of the Census, who spent Census night in Australia. People are counted where they were at the time of the Census, which may not be where they usually live. In contrast, usual residence Census counts are counts of all people, based on where they usually live, rather than where they were on Census night. Overseas visitors in Australia are excluded from usual residence data.

15 Early population estimates were obtained through colonial musters and, from 1828, through a series of relatively regular colonial censuses. The dates of these colonial censuses are shown in the following table. In 1910, on the basis of the early musters and other colonial records, an annual series of population totals for the states was published for all years commencing from December 1788, the year of European colonisation of Australia. They are disaggregated by sex from 1796. Annual counts of the population by single year of age and sex for Australia as a whole commenced in 1921 and for the individual states and territories in 1962. Prior estimates of the population by age and sex were only available for Census years.

16 The first national Census was taken in 1911 (April 3), it was followed by others in 1921 (April 4), 1933, 1947, 1954 and 1961. Since 1961, Censuses have been conducted every five years. From 1933 to 1986, the Census was held on June 30. With the move from three- to four-term school years in the 1980s, June 30 is now on or around the time of school holidays and therefore later Census dates were chosen to reduce the number of people being counted away from home. Since 1991, Censuses have been held on August 6 (1991 and 1996 censuses), August 7 (2001), August 8 (2006) and (August 9) 2011 and 2016.

17 National, state and territory population estimates from Federation (1901) to 1971 are based on Census counts on an actual location basis, updated for post-censal years according to registered births and deaths by state/territory of registration, and interstate and overseas migration.

18 From 1971, the concept of estimated resident population (ERP) is used, which links people to their place of usual residence (that is, where people usually live). ERP was introduced following the 1981 Census and backdated to 1971. The place of usual residence conceptual basis for population estimates is detailed in Information Paper: Population Concepts, 2008(cat. no. 3107.0.55.006) and Population Estimates: Concepts, Sources and Methods, 2009(cat. no. 3228.0.55.001).

19 For Census dates, ERP is derived from usual residence Census counts, to which are added the estimated net Census undercount and Australian residents estimated to have been temporarily overseas at the time of the Census. Overseas visitors in Australia are excluded.From the Census base, ERP is updated by adding to the estimated population at the beginning of each period the components of natural increase (on a usual residence basis) and net overseas migration. For the states and territories, interstate migration is also taken into account.

20 After each Census, estimates for the preceding intercensal period are revised to ensure that the total intercensal increase agrees with the difference between the ERPs at the two 30 June dates in the respective Census years.

21 Following the 2011 Census, ERP was recast data back to 1991. While previous ERP levels changed, growth rates remained relatively consistent with previously-published estimates. Fertility, mortality, and other measures which use ERP as a denominator in this publication have also been revised back to 1991 (unless otherwise indicated). For further information, see Final Rebasing of Australia's Population Estimates, December Quarter 2012 and Recasting 20 Years of ERP.

22 From July 1976, final intercensal difference is recorded as a separate component of population change. For the period July 1971 to June 1976 no intercensal difference exists due to the method used to produce resident population estimates. Prior to July 1971, intercensal differences were incorporated into the overseas and interstate migration components of population change. See Glossary for more information.

23 Population estimates for each reference date are presented based on a consistent statistical geography, however caution must be exercised when comparing populations across time as they may be based on different boundaries. Refer to the footnotes for each table for more information about statistical geography used in that table. For further information refer to the ABS Geography home page.

24 The regions specified in this publication are Greater Capital City Statistical Areas (GCCSAs), Significant Urban Areas (SUAs), Local Government Areas (LGAs), and urban and rural areas. GCCSAs represent the socioeconomic area of each of the eight state and territory capital cities. SUAs represent concentrations of urban development with populations of 10,000 people or more. LGAs are legally designated areas over which incorporated local governments have responsibility. 

25 Urban and Rural areas are as defined for the Census conducted on or near the reference date. In the 2016 Census, Urban and Rural areas were based on the ABS Section of State structure, which aggregates Urban Centres and Localities on the basis of population ranges. Urban areas represent combinations of Urban Centres, Rural areas represent the remaining parts of the country including Bounded Localities. Urban and Rural areas were defined similarly in earlier Censuses.

26 Regional population estimates based on the concept of usual residence have been produced since the 1970s. Prior to this, population figures were calculated on an actual location concept. Estimates based on actual location are generally higher in areas which attract short-term migrants, such as tourist areas, and this break in time series should be noted when comparing historical population estimates. For further information on regional population estimates, see Regional Population Growth, Australia (cat. no. 3218.0).

27 Registration of births is the responsibility of state and territory Registrars of Births, Deaths and Marriages. Births information is based on data provided on an information form completed by the parent(s) of the child. This form is the basis of data provided to the ABS by individual Registrars for compilation into aggregate statistics. For further information, see Births, Australia (cat. no. 3301.0).

28 Unless otherwise indicated, birth statistics refer to live births registered during the calendar year shown. There is usually an interval between the occurrence and registration of a birth, and as a result, some births occurring in one year are not registered until the following year, or even later. This can be caused by either a delay by the parent(s) in submitting a completed form to the registry, or a delay by the registry in processing the birth.

29 Birth prior to 1969 are presented on the basis of state or territory of registration. From 1969 onwards they are presented on the basis of the state or territory of usual residence of the mother, regardless of where in Australia the birth occurred or was registered. Births which take place outside Australia are excluded from the statistics.

30 Births to mothers who are usual residents of Australia's Other Territories are registered in other Australian states. Prior to 1993, births to mothers usually resident in Christmas Island and Cocos (Keeling) Islands were included with Offshore Areas and Migratory in Western Australia, while births to mothers usually resident in Jervis Bay Territory were included with the ACT. Births occurred on Norfolk Island from 1 July 2016 are included in Other Territories.

31 Registration of deaths is the responsibility of the state and territory Registrars of Births, Deaths and Marriages. Information about the deceased is based on details supplied by a relative or other person acquainted with the deceased, an official of the institution where the death occurred, and on information supplied by a medical practitioner or a coroner as to the cause of death. This information is supplied to the ABS by the state and territory registrars for coding and compilation into aggregate statistics. For further information see Deaths, Australia (cat. no. 3302.0). 

32 Unless otherwise indicated, death statistics refer to deaths registered during the calendar year shown. There is usually an interval between the occurrence and registration of a death (referred to as a registration 'lag') and as a result, some deaths occurring in one year are not registered until the following year or even later. This can be caused by either a delay in the submission of a completed form to the registry, or a delay by the registry in processing the death. Deaths which occur in November and December are also likely to be registered in the following year.

33 Death statistics prior to 1971 are presented on the basis of state or territory of registration. From 1971, they are presented on the basis of the state or territory of usual residence of the deceased, regardless of where in Australia the death occurred or was registered. 

34 Deaths of overseas visitors in Australia are included in the statistics, and are classified according to the state or territory in which the death was registered. Deaths of Australian residents which took place outside Australia are not included in the statistics. 

35 As deaths of Australian residents which took place overseas are not included in the statistics, deaths of Australian troops overseas in World War I are excluded. Similarly, Australian troops who died overseas during World War II are not included in death statistics, however they have been removed from the population estimates.

36 Life expectancy statistics are calculated using life tables. A life table is a statistical model used to represent the mortality of a population. In its simplest form, a life table is generated from age-specific death rates and the resulting values are used to measure mortality, survivorship and life expectancy.

37 Life tables are presented separately for males and females. The life table depicts the mortality experience of a hypothetical group of newborn babies throughout their entire lifetime. It is based on the assumption that this group is subject to the age-specific mortality rates of the reference period. Typically this hypothetical group is 100,000 in size. 

38 Since 1995, life tables produced by the ABS differ from those published prior to 1995 in a number of important respects. Firstly, they are based on three years of deaths and population data. This is intended to reduce the impact of year-to-year statistical variations, particularly at younger ages where there are small numbers of deaths, and at very older ages where the population is small. Secondly, the deaths and population data are based on Australian residents who are physically present in Australia over the three-year period i.e. Australian residents temporarily overseas are excluded as are deaths in Australia of overseas visitors. Thirdly, they have been actuarially graduated on the same principles which are used for the quinquennial Australian life tables prepared by the Australian Government Actuary. Fourthly, from 2012 a small refinement has also been made to the method to bring Australia's mortality rates (qx values) into line with other comparable countries. For further information, see Life Tables, Australia (cat. no. 3302.0.55.001).

39 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 estimating NOM, and thereby Australia's official ERP, a person is regarded as a usual resident if they have been (or expect to be) residing in Australia for a period of 12 months or more over a 16 month period. As such, NOM and ERP estimates include all people, regardless of nationality, citizenship or legal status, who usually live in Australia, with the exception of foreign diplomatic personnel and their families.

40 Conceptually, the term NOM is based on an international traveller's 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). This 12 month period does not have to be continuous and is measured over a 16-month reference period. Therefore, 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.

41 Administrative information on persons arriving in, or departing from, Australia is collected via various processing systems, passport documents, visa information, and incoming passenger cards. 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 Australian Government Department of Home Affairs (Home Affairs) under the authority of the Migration Regulations 1994 made under the Migration Act 1958.

42 ABS statistics on overseas migration are mainly compiled using information from Home Affairs sources.

43 Each month all overseas arrivals and departures (OAD) movement records are processed by the ABS to produce OAD statistics. This processed OAD data is then used to produce quarterly NOM estimates. Statistics on OAD and related data quality issues are published on a monthly basis in Overseas Arrivals and Departures, Australia (cat. no. 3401.0). Quarterly NOM estimates contribute to quarterly ERP and are released in Australian Demographic Statistics (cat. no. 3101.0).

44 Statistics on overseas migration exclude: multiple movements; 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 undocumented arrivals. From 1 July 2006 onwards, foreign diplomatic personnel and their families are also excluded.

45 During a reconciliation of 1996-2001 intercensal population growth estimates (including measures of immigration, emigration and NOM) with the results of the 2001 Census of Population and Housing, the ABS identified that inconsistent results were arising from a 1998 passenger card processing change and the measurement of temporary visitors' duration of stay in Australia, or Australian residents' temporary duration of absence from Australia.

46 The ABS noted that the precise measurement of duration of stay in Australia or absence from Australia using a comparison of border crossing transactions may lead to a misleading categorisation of frequent travellers to short-term, when their overall period of stay or absence in a broader context was long-term punctuated by short journeys. This was because after the passage of time, they may not spend a continuous period of 12 months in Australia during their long-term period of stay in Australia or outside of Australia for absences from Australia. This was inconsistent with the intention behind the definition of a long-term migrant as set out in the United Nations Recommendations on Statistics of International Migration, Revision 1 (1998, 18) and the ABS Estimated Resident Population conceptual definition. The use of single continuous periods of stay as the criteria (i.e. 12 continuous months) for classifying travellers into the non-permanent migration categories was seen as a major shortcoming in the measurement of NOM and consequently estimates of Australia's resident population.

47 Further, there were some travellers such as permanent immigrants and emigrants who were not asked their intended duration of stay or absence on Australian passenger cards, yet it was observed that after a passage of less than a year, some permanent immigrants departed Australia and some permanent emigrants returned to Australia. The ABS also identified a need to convert the multiple border movements information for frequent travellers within a reference period to individual person estimates together with their travel history over time to avoid double counting.

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

49 The ABS developed and introduced an improved method, called the '12/16 month rule' methodology, for estimating NOM. It has been used in calculating Australia's official ERP since September quarter 2006. The '12/16 month rule' methodology 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.

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

51 Due to the removal of the outgoing passenger card on 1 July 2017, the ABS has further reviewed its NOM statistics, methodology and processing systems. Historical NOM data from September quarter 2011 onwards has been produced based on the new methods and has been used in the 2011-2016 intercensal period as part of the final rebasing of population estimates. As NOM estimates cannot be finalised until 16 months after the reference period, NOM is subject to revision. Testing has shown that the revision between preliminary and final NOM using the new methodology has improved when compared to the previous method.

52 For further information on the improvements to NOM estimation over time and changes to the revision schedule for NOM, see:

• Information Paper: Improving Net Overseas Migration Estimation, Mar 2010 (cat. no. 3412.0.55.001), and
• Information Paper: Further Improvements to Net Overseas Migration Estimation, Dec 2013(cat. no. 3412.0.55.002), and
• Information Paper: Improvements to the Estimation of Net Overseas Migration, Mar 2018(cat. no. 3412.0.55.004).
   

53 For further information on the '12/16 month rule' methodology, see:

• Information Paper: Improved Methods for Estimating Net Overseas Migration, Australia, 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), and
• Technical Note: '12/16 month rule' Methodology for Calculating Net Overseas Migration from September quarter 2006 onwards in Migration, Australia 2014-15 (cat. no. 3412.0).
   

54 The '12/16 month rule' means a 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 period of 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 individual's actual travel behaviour (or models this behaviour for preliminary NOM).

55 To measure a traveller's actual duration of stay, the ABS uses a unique personal identifier provided with the administrative data supplied by Home Affairs. To be able to apply the '12/16 month rule', the personal identifier is used to match a traveller's movements over time and construct a movement history for each arrival and departure record.

56 Conceptually, NOM estimates are 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.

57 One of the central changes with the '12/16 month rule' 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.

58 The methodology and estimation system adopted by the ABS for measuring NOM and the contribution to Australia's ERP more closely aligns with the international definitions set out by the United Nations. The ABS has not changed the statistical conceptual definition of NOM. However, the method of measurement has changed.

59 Prior to 1 July 2006, NOM estimation methods used a '12/12 month rule' to determine if a traveller contributed to ERP. This meant that in order for a person to contribute to NOM they must stay in or be absent from Australia for a continuous period of 12 out of 12 months. It compared data on actual travel movements over a 12 month period with data on individual travellers' duration of stay as recorded on their passenger cards. In order to conduct such a comparison, data for a 15 month period (i.e. one year plus one quarter) were required. For more information, 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.

60 Many overseas travellers stay (or are away) shorter or longer periods than initially intended, as recorded on their passenger cards. From July 1982 to June 1997, NOM estimates included an adjustment for the net effect of category jumping. Category jumping is 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. Twelve months after a reference period it can be determined whether the number of initially recorded short-term, long-term and permanent arrivals and departures matched actual patterns of movement.

61 For example, some visitors on arrival may state that they intend to stay in Australia for more than 12 months. However, they may change their travel plans and depart the country after only six months. Since migration figures were affected by this change in travel behaviour, an adjustment was incorporated into the NOM estimate and ERP.

62 The method used to estimate category jumping up until June 1997 inclusive was based on aggregate flows of traveller movements rather than individual travellers. Until June 1998, the measurement of duration of stay or absence on the second leg of travel was based on passenger reporting on the arrival or departure card. This self-reported duration was used to determine the time at which a person arrived (for visitors) or left Australia (for Australian residents). However, from July 1998 onwards, implementation of a new passenger card design and processing system enabled the Department of Immigration and Multicultural Affairs (now Home Affairs) to derive actual duration of stay or absence for the second leg of travel by matching both the actual arrival and departure movement dates rather than relying on passengers reporting their duration of stay or absence.

63 Despite this improvement in the quality of actual duration of stay or absence data for the second leg of travel, the above estimation method appeared incapable of producing acceptable estimates of category jumping. Given that category jumping had only a small effect on ERP and that estimates produced by the above method seemed highly volatile, the ABS set category jumping estimates to zero until an improved estimation technique was developed. They were set to zero from September quarter 1997 to June quarter 2001.

64 Through the provision of additional data from Home Affairs, the ABS had the ability to match traveller movements over time. This enabled a movement history to be constructed for those arriving and departing and thus calculate an actual duration of stay. Matching traveller movements enabled the adjustment of permanent and long-term movement. This adjustment (termed 'migration adjustment') allowed for components of NOM to be presented on an adjusted basis.

65 For more information on category jumping and the interim methods of adjusting NOM for the previous (12/12) method, see Demography Working Paper 2003/5 - Net Overseas Migration: Adjusting for Actual Duration of Stay or Absence (cat. no. 3137.0). Adjustments applied to overseas migration estimates have also been discussed in a special article in Migration, Australia, 2002-03 (cat. no. 3412.0).

66 Due to changes in the methods used to adjust NOM estimates, caution should be used when comparing estimates over time. The following table describes the adjustment methods applied to NOM estimates from September quarter 1996.

67 During World War I, troops leaving Australia were regarded as emigrants, while those returning were regarded as immigrants. This largely explains the record loss in 1916, and a large migration gain in 1919. During World War II, troop movements between September 1939 and June 1947 were excluded from calculations of overseas migration.

68 Australia's ERP and estimates of NOM include all people, regardless of nationality or citizenship, who usually live in Australia, with the exception of foreign diplomatic personnel and their families. Therefore, foreign diplomatic personnel and their families are considered out of scope and were removed from NOM estimates from 1 July 2006. The previous methodology for estimating NOM was unable to exclude diplomatic personnel and their families.

69 Interstate migration is a key determinant of the accuracy of state and territory population estimates. Interstate movements cannot be directly estimated. Instead, post-censal estimates of interstate migration are modelled using administrative by-product data. Currently, the data used by the ABS are information on interstate changes of address advised to Medicare Australia and to the Department of Defence in the case of the military.For further information, see Information Paper: Evaluation of Administrative Data Sources for Use in Quarterly Estimation of Interstate Migration (cat. no. 3127.0.55.001).

70 Medicare is Australia's universal health insurance scheme and covers the vast majority of Australian residents. De-identified Medicare change of address counts are provided to the ABS by the Department of Human Services, and aggregated to state and territory levels. The data is lagged by three months to account for the time between a person changing address and updating their details with Medicare. Expansion factors are applied, by age, sex and state/territory, to account for recognised undercoverage of movers across sex and age groups in the Medicare data. These factors are calculated by calibrating Medicare migration data with migration data from the previous Census, at the age, sex, state of arrival and state of departure departure levels.

71 For defence force personnel, who access other health services and therefore do not use Medicare, the ABS uses aggregated defence force personnel movements provided by the Department of Defence. This data reflects of the time of move, and is therefore is not lagged.

72 The Medicare- and defence-based data are combined to create estimates of interstate migration for all usual residents. The interstate migration model is updated when new Census information becomes available, and interstate migration estimates back to the previous Census are recalculated (rebased). For further information see 2016 Census update of the net interstate migration model (Technical Note).

73 The ABS statistics on OAD are calculated using administrative data collected and compiled by Home Affairs under the authority of the Migration Regulations (Migration Act, 1958). The monthly OAD publication contains statistics on the travel movements of all persons arriving in, and departing from, Australia. Its main focus is to provide information and analysis of short-term movements (i.e. less than one year), in particular short-term visitor arrivals and short-term resident returns. Statistics on overseas arrivals and departures relate to the number of movements of travellers rather than the number of travellers. Individuals who travel multiple times in a year are counted each time they cross Australia's borders. Permanent and long-term movements from OAD statistics are not an appropriate source of migration statistics.

74 From 1 July 2017, travellers leaving Australia are no longer required to complete an Outgoing Passenger Card (OPC). Due to the removal of the OPC by the Department of Home Affairs, the ABS undertook a review of its OAD statistics, methodology and processing systems. This provided an opportunity to consider alternative data sources and ways to make better use of a range of existing data collected by Home Affairs about Australia's international border crossings. Detailed information on the changes and improvements arising from the 2017 review of OAD statistics appears in the Data Quality Issues (Data Quality Issues Appendix) in the Explanatory Notes section in Overseas Arrivals and Departures, Australia (cat. no. 3401.0).

75 The review resulted in a break in series, necessitating a revised time series for OAD data from July 2007 to June 2017 based on the new methodology. Figures prior to June 2007 may not be strictly comparable to those which follow.

76 OAD statistics 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, of transit passengers who pass through Australia but are not cleared for entry, and of passengers on pleasure cruises commencing and finishing in Australia. Similarly, these statistics exclude undocumented arrivals or departures.

77 Prior to 1959, overseas arrivals and departures were classified as either permanent or temporary. Revised questions for travellers were introduced from 1 January 1959 which enabled arrivals and departures previously classified as permanent to be subdivided (as from 1 January 1959) into two categories: permanent movement and long-term movement.

78 OAD statistics are derived from a combination of full enumeration and sampling. From July 2007, all departures are fully enumerated. All permanent arrivals and all arrivals with a duration of one year or more (long-term arrivals) are also fully enumerated. However, all arrivals with a duration of less than one year (short-term arrivals) are sampled. While the total number of travellers and their citizenship is fully known, statistics for other characteristics of short-term arrivals (such as their state/territory of stay/residence) are based on a sample and may differ slightly from those that would be obtained from complete processing. From July 2007, about 5% of all short-term arrivals have been selected for sample.

79 Some statistics relating to these movements are therefore estimates which are subject to sampling variability, that is, they may differ from statistics which would have been obtained if details of all these movements had been processed.

80 Country of birth classifications used by the ABS and preceding statistical agencies have changed over time. Tables presented in Australian Historical Population Statistics display the country of birth classifications in existence at the time of production of the data. For more detailed information on the most recent classification of countries, refer to the ABS publication Standard Australian Classification of Countries (SACC), 2016 (cat. no. 1269.0).

81 Estimates of the Aboriginal and Torres Strait Islander population were first produced by the ABS in 1994, in Experimental Estimates of the Aboriginal and Torres Strait Islander Population, 1986 to 1991 (cat. no. 3230.0). Estimates of the Aboriginal and Torres Strait Islander population based on the 2016 Census were released in Estimates of Aboriginal and Torres Strait Islander Australians, June 2016 (cat. no. 3238.0.55.001), and a time series of estimates and projections based on the 2016 Census is scheduled for release in 2019.

82 There are no accurate estimates of the population of Australia before European settlement. Many estimates were based on post-1788 observations of a population already reduced by introduced diseases and other factors. Smith (The Aboriginal Population of Australia (1980) by L.R. Smith, Australian National University Press for the Academy of Social Sciences in Australia, Canberra (1980)) estimated the absolute minimum pre-1788 population at 315,000. Other estimates put the figure at over one million people, while recent archaeological evidence suggests that a population of 750,000 could have been sustained.

83 Until 1967, section 127 of the Constitution required the exclusion of 'Aboriginal natives' from estimates of the population of Australia. 'Aboriginal natives' were interpreted as being people who had more than 50% Aboriginal 'blood'. This provision was repealed with the proclamation of the Constitution Alteration (Aboriginals) Act 1967 so that since 10 August 1967 population statistics were to officially include 'full-blooded' Aboriginal and Torres Strait Islander people. 

84 From the 1971 Census, Aboriginal and Torres Strait Islander persons have no longer been asked to state their degree of Aboriginal and Torres Strait Islander descent. Since this time, in 1996 for example, the Census question has asked 'Is the person of Aboriginal or Torres Strait Islander origin?'. Changing social attitudes, political developments, improvements in Census coverage and a broader definition of 'Aboriginal' and 'Torres Strait Islander' are likely to have contributed to the rapidly rising numbers of Aboriginal and Torres Strait Islander people that have been recorded since 1971. For further information on increases in Aboriginal and Torres Strait Islander population counts between Censuses, refer to Census of Population and Housing: Understanding the Increase in Aboriginal and Torres Strait Islander Counts (cat. no. 2077.0).

85 Since 1981, all ABS Aboriginal and Torres Strait Islander population statistics are based on responses to the ABS standard question for Aboriginal and Torres Strait Islander identification, which is used in self-enumerated collections. The same Census question has been used to determine Aboriginal and Torres Strait Islander status since the 1981 Census.

86 Data based on Marriages, Divorces and Marital Status were discontinued from this product after 2008, as data on registered marriages became less relevant to the formation of partnerships and families due to the increasing incidence of social (or de facto) marriages. The 2008 release of this product provides data on marriages, divorces and marital status up until 2006.

87 For more information on Marriages, Births and Marital Status, see:
Marriages, Australia (cat. no. 3306.0.55.001)
Marriages and Divorces, Australia (cat. no. 3310.0)
Divorces, Australia (cat. no. 3307.0.55.001)

Data on marriages and divorces are no longer included in this publication. See Explanatory Note 3 for further information.

88 All data are affected by errors in reporting and processing. Registered births and deaths data are also affected by delays in registration. In this release, estimates and their components have sometimes been rounded. Both rounded and un-rounded figures should not be assumed to be accurate to the last digit shown, and no reliance should be placed on statistics with small values. In commentary based on statistics in this release, it is recommended that the relevant statistics be rounded. Where figures have already been rounded, discrepancies may occur between sums of component items and totals.

89 The Census and Statistics Act, 1905 provides the authority for the ABS to collect statistical information, and 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. This requirement means that the ABS must take care and make assurances that any statistical information about individual respondents cannot be derived from published data.

90 Some techniques used to guard against identification or disclosure of confidential information in statistical tables are suppression of sensitive cells, and random adjustments to cells with very small values. Throughout this publication, different methods of confidentialisation have been used. In some cases cell values have been suppressed and are not available for publication but included in totals where applicable. In these cases data may not sum to totals due to the confidentialisation of individual cells.

91 ABS publications draw extensively on information provided freely by individuals, businesses, governments and other organisations. Their continued cooperation is very much appreciated; without it, the wide range of statistics published by the ABS would not be available. Information received by the ABS is treated in strict confidence as required by the Census and Statistics Act, 1905.

92 ABS publications which may be of interest to users include:

• Australian Demographic Statistics (cat. no. 3101.0)
• Births, Australia (cat. no. 3301.0)
• Catalogue of Australian Statistical Publications, 1804 to 1901 (cat. no. 1115.0)
• Deaths, Australia (cat. no. 3302.0)
• Demography (for each state and territory) (cat. no 3311.1 - 3311.8)
• Demography (for Australia and each state and territory) (cat. no. 3311.0.55.001 - 3311.7.55.001)
• Demography, 1900 to 1971, Commonwealth Bureau of Census and Statistics (Ref. no. 4.9)
• Demographic Estimates and Projections: Concepts, Sources and Methods (cat. no. 3228.0)
• Estimates and Projections, Aboriginal and Torres Strait Islander Australians, 2001 to 2026(cat. no. 3238.0)
• Life tables (for Australia and each state and territory) (cat. no. 3302.0.55.001 - 3302.8.55.001)
• Migration, Australia (cat. no. 3412.0)
• Overseas Arrivals and Departures, Australia (cat. no. 3401.0)
• Population by Age and Sex (for Australia and each state and territory) (cat. no. 3235.0.55.001 - 3235.8.55.001)
• Population by Age and Sex, Australian States and Territories (cat. no. 3201.0)
• Regional Population Growth, Australia (cat. no. 3218.0)
• Year Book, Australia (cat. no. 1301.0)