EXPLANATORY NOTES

INTRODUCTION

1 This publication presents counts from the 2011 Census of Population and Housing for people who both identified as being of Aboriginal and Torres Strait Islander origin and were counted in the Census.

2 The 2011 Census of Population and Housing was held on 9 August 2011. The objective of the Census is to accurately measure the number and key characteristics of people in Australia and the dwellings in which they live, on Census Night. This provides a reliable basis for the estimation of the population of each of the states, territories and local government areas primarily for electoral purposes and the distribution of government funds. It also provides information about the characteristics of the population and its housing within small geographic areas and for small population groups. Census data supports a range of planning, administration, policy development and evaluation activities of government and other data users.


INDIGENOUS STATUS

3 The question about Indigenous status on the Census form asks whether each person is of Aboriginal and/or Torres Strait Islander origin. The Commonwealth definition of an Aboriginal or Torres Strait Islander person is:

• a person of Aboriginal or Torres Strait Islander descent who;
• identifies as being of Aboriginal or Torres Strait Islander origin and who is;
• accepted as such by the community with which the person associates.

4 The 1996 Census was the first Census to allow people's origins to be recorded as both Aboriginal and Torres Strait Islander; prior to this, only one or the other could be recorded. This question format is the Standard Indigenous Question and has been repeated in subsequent Censuses, including the 2011 Census.

5 For more information on definitional changes and Census questions, refer to the Census Dictionary, 2011 (cat. no. 2901.0).


SCOPE AND COVERAGE

6 The 2011 Census of Population and Housing was held on 9 August 2011. Australia's first national Census was held in 1911 and since 1961 a Census has been taken every five years, the frequency specified in the Census and Statistics Act (1905). 7 Following changes to the Australian Constitution as a result of the 1967 Referendum, Aboriginal and Torres Strait Islander peoples were included in official estimates of the Australian population. As a consequence, from the 1976 Census onwards, the Australian Bureau of Statistics (ABS) has developed and improved strategies to count the Aboriginal and Torres Strait Islander population throughout Australia. 8 The Census aims to count every person who spent Census Night in Australia. This includes Australian residents in Antarctica and Other Territories - Jervis Bay, Cocos (Keeling) Islands and Christmas Island. The other Australian External Territories (Norfolk Island and minor islands such as Heard and McDonald Islands) are outside the scope of the Australian Census. The only people who are excluded from the Census are foreign diplomats and their families.

9 The Census includes people on vessels in or between Australian ports as well as people on board long distance trains, buses or aircraft. Also included are those people outside Australia who are not required to undertake migration formalities, such as those on oil and gas rigs or on Australian Antarctic bases. People entering Australia before midnight on Census Night are counted, while people leaving an Australian port for an overseas destination before midnight on Census Night are not. Visitors to Australia are included regardless of how long they have been in the country or how long they plan to stay. However, for people who intend to be in Australia for less than 12 months, only basic demographic data are available. The Census includes homeless people and people camping out.

10 All occupied dwellings are counted in the Census with the exception of diplomatic dwellings. Unoccupied private dwellings are also counted, with the exception of unoccupied dwellings in caravan parks, marinas and manufactured home estates (self-contained dwellings that are built off-site and then transported to the estate for installation). Unoccupied residences of owners, managers or caretakers of such establishments are counted.

11 Census counts are not adjusted for undercount (that is, people missed in the Census) and overcount (people counted more than once in the Census). It is likely that some Aboriginal and Torres Strait Islander people, particularly those aged 15-24 years, may have been missed in the 2006 Census but counted in the 2011 Census, and vice versa. Although the Post Enumeration Survey (PES) illustrated the net undercount for both Censuses by broad demographic features, it is not possible to produce detailed estimates of the net undercount for the Aboriginal and Torres Strait Islander population. As a result, the effect of undercount has been ignored when making comparisons between the two Censuses, though referenced where it was likely to be most acute.


ENUMERATION PROCEDURES

12 In order to achieve the most accurate count of Aboriginal and Torres Strait Islander peoples in the Census, the ABS developed an Indigenous Enumeration Strategy. This Strategy was first introduced in the 1976 Census for remote areas of WA and NT, and has been expanded and improved for subsequent Censuses. The strategy aims to be culturally appropriate and to raise the quality of the Census counts for this population group.

13 The 2011 Census Indigenous Enumeration Strategy incorporated improvements to enumeration of Aboriginal and Torres Strait Islander people living in urban areas, as well as those living in discrete Aboriginal and Torres Strait Islander communities. At a broad level, the improvements for the 2011 Census included:

• earlier and ongoing engagement
• a reduction in the overall enumeration period for Aboriginal and Torres Strait Islander communities
• an increase in the number of field staff recruited
• a greater level of support to Aboriginal and Torres Strait Islander people requiring assistance in completing their form, in both urban and remote areas.

14 In most discrete Aboriginal and Torres Strait Islander communities, an interview approach was used, with many local people employed and trained to conduct or facilitate the interviews.

15 In pre-identified urban areas increased support and assistance were provided to Aboriginal and Torres Strait Islander people, including the option of collecting Census information through an interview.

16 For more information on the Indigenous Enumeration Strategy refer to 2011 Census Fact sheet Enumeration Procedures for Aboriginal and Torres Strait Islander Peoples available on the ABS website.


LIMITATIONS OF CENSUS DATA

17 There are four principal sources of error in Census data: respondent error, processing error, partial response and undercount. Quality assurance processes in the Census program aim to reduce error as much as possible, and to provide a measure of the remaining error to data users, to allow them to use the data in an informed way.

18 The Census Dictionary, 2011 (cat. no. 2901.0) provides more information on managing Census data quality.


DATA PRESENTATIONS AND CONSIDERATIONS

19 The proportions of the population shown in the tables in this publication include 'not stated' responses in the denominator. For example, the proportion of people in Australia who are of Aboriginal and/or Torres Strait Islander origin is calculated by dividing the number of persons identified as Aboriginal and/or Torres Strait Islander origin by the total population in the Census, and expressing the result as a percentage. The 'total population' includes records coded to 'not stated'.

20 The Census counts presented in this publication are based on usual residence. For information on usual residence and place of enumeration refer to the Census Dictionary, 2011 (cat. no. 2901.0).

21 Under the Census and Statistics Act (1905) it is an offence to release any information collected under the Act that is likely to enable identification of any particular individual or organisation. Care is taken in the specification of tables to minimise the risk of identifying individuals. In addition, a technique has been developed to randomly adjust cell values. Random adjustment of the data is considered to be the most satisfactory technique for avoiding the release of Census data that may identify individuals. When the technique is applied, all cells are adjusted to prevent any such data being exposed. These adjustments result in small introduced random errors. However, the information value of the table as a whole is not impaired. For more detail refer to introduced random error in the Census Dictionary, 2011 (cat. no. 2901.0).

22 Various analyses in this publication attempt to track age cohorts over time to assess whether the changes that occurred in each cohort were in line with expectations. This is generally done by following selected age groups of Aboriginal and Torres Strait Islander people back in time (for example, from 2011 back to 2006) using age cohorts. In the case of total fertility rates, it is done by following Aboriginal and Torres Strait Islander women aged 45-49 years from an earlier period forward to a later period using age cohorts. An age cohort is a group of people with the same birth year within a defined period (for example, people aged 30-34 years in 2011 were aged 25-29 years in 2006). Mortality and mobility have not been taken into account in the age cohort analyses. Changes in age cohorts are discussed in more detail in Changes in Age and Sex Structure.

23 In 2011, almost half (48%) of Aboriginal and Torres Strait Islander people reported living at a different address five years ago, and some of this mobility would have resulted in them living in a different Remoteness Area. However, there are technical challenges to be overcome in coding a person's usual residence five years ago to a Remoteness Area. While this presents a limitation in the analysis provided in Changes in Distribution of Census Counts by Remoteness, the analysis is still considered to be informative.


MEASURES OF FERTILITY AND MATCHING CHILDREN TO MOTHERS

24 Total fertility rate (TFR) is the most commonly used summary measure of fertility. The TFR is the sum of age-specific fertility rates (live births at each age of mother per 1,000 of the estimated female population of the same age), which represents the number of children a female could expect to bear during her lifetime if she experienced current age-specific fertility rates at each age of her reproductive life.

25 There are several approaches to estimating levels and trends of TFRs. For example, it is possible to use the birth registrations data as published annually in Births, Australia (cat. no. 3301.0), or apply the own-children method to Census data to estimate fertility rates 15 years prior to the Census.¹ The own-children method is a Census-based reverse survival technique which matches children to mothers in households, classified by age of child and mother, to produce estimates of: (a) births by age of mother; and (b) number of women by age in the years prior to the Census. Reverse survival methods used to produce backcasted Aboriginal and Torres Strait Islander population estimates use data from life tables (of which the 2010-2012 life tables will be released on 15 November 2013). These estimates are then used to produce age-specific birth rates for the years between Censuses.

26 Caution is advised, as estimates derived from both birth registrations data and the own-children method have known limitations, which are particularly challenging for the Aboriginal and Torres Strait Islander population. Estimated fertility using birth registrations data may underestimate the fertility level of Aboriginal and Torres Strait Islander women because some births of Aboriginal and Torres Strait Islander people are not reported and recorded as such when they are registered - for further information refer to Births, Australia (cat. no. 3301.0). In applying the own-children method, not all children can be matched with their biological mothers and so two assumptions are used: (a) for non-matched children, the proportion of them belonging to non-Indigenous mothers is assumed to be the same as for those of matched 'own-children'; and (b) the age distribution of non-matched mothers is the same as that for matched mothers. The choice of a life table is also very important. As a result of these limitations, there is considerable uncertainty associated with estimated levels of fertility and it is more appropriate to examine the trends of fertility over time rather than fertility figures at a point of time.

27 The Family-Tree method is an extension of the own-children method.² It appends information of parents and/or grandparents and/or spouse, where applicable, to each individual record. Since the family household is defined in Census based on couple and parental relationships, it is possible to append information of 'social' parentage rather than biological links. When matching mothers with their biological children, these refined procedures can match, on average, about 5% more children to their mothers than the own-children method. It is important to note that the Family-Tree method involves constructing connections between individuals within Census data, and does not involve any genealogical (or ‘family history’) methodology.

28 According to Births, Australia, 2011 (cat. no. 3301.0), from 2006 to 2011, about 71-73% of Aboriginal and Torres Strait Islanders babies were born to Aboriginal and Torres Strait Islander mothers. This rate is higher than that obtained from the Family-Tree method using Census data (68% for children aged less than one year in 2006 and 67% in 2011). This might be an indication that some parents did not identify their child as an Aboriginal and/or Torres Strait Islander person in the Census but did so in the birth registration.


POPULATION ESTIMATES

29 Estimated Resident Population (ERP) is the official measure of the population of Australia. It is based on the concept of usual residence. It refers to all people, regardless of nationality, citizenship or legal status, who usually live in Australia, with the exception of foreign diplomatic personnel and their families. It includes usual residents who are overseas for less than 12 months. It excludes overseas visitors who are in Australia for less than 12 months. In the compilation of the ERP, important adjustments are made to the Census count based on place of usual residence. For further information about ERP, see Australian Demographic Statistics (cat. no. 3101.0).

30 The ABS is undertaking a program of work based on results of the 2011 Census of Population and Housing and the 2011 Census Post Enumeration Survey (PES) to compile and release estimates of the Aboriginal and Torres Strait Islander population at 30 June 2011. Preliminary estimates at 30 June 2011 are available in Australian Demographic Statistics (cat. no. 3101.0) from the March quarter 2012 issue (released on 27 September 2012) onwards. These preliminary estimates are published by five year age groups, sex and state/territory of usual residence. Further disaggregation will be available when the final estimates of the Aboriginal and Torres Strait Islander population at 30 June 2011 are published in Estimates of Aboriginal and Torres Strait Islander Australians, June 2011 (cat. no. 3238.0.55.001).

31 For further information regarding this work program see Information Paper: Aboriginal and Torres Strait Islander Demographic Statistics Work Program and Release Plans, Apr 2012 (cat. no. 3238.0.55.003).


RELATED INFORMATION

32 Additional information on data quality in the 2011 Census is available on the ABS website and the Census portal. Specific information on non-response rates, and conceptual and data issues can also be found on the Census portal.

33 Information on the quality of Aboriginal and Torres Strait Islander births data is available in Births, Australia (cat. no. 3301.0).

34 Information on the quality of Aboriginal and Torres Strait Islander deaths data is available in Deaths, Australia (cat. no. 3302.0).


FOOTNOTES

¹ Cho, Lee-Jay; Retherford Robert and Minja Kim Choe. (1986). The Own-Children Method of Fertility Estimation. University of Hawaii Press.
² Zhang, Guangyu and Campbell, Paul (2012). ‘Developing a Family-Tree method to maximise the use of Census data’ Paper presented at the 16th Biennial Conference of the Australian Population Association, 5-7 December, Melbourne.