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3238.0.55.001 - Estimates of Aboriginal and Torres Strait Islander Australians, June 2011 Quality Declaration 
Latest ISSUE Released at 11:30 AM (CANBERRA TIME) 30/08/2013   
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TECHNICAL NOTE 1 ESTIMATED RESIDENT ABORIGINAL AND TORRES STRAIT ISLANDER POPULATION – METHOD OF CALCULATION


INTRODUCTION

1 This technical note outlines the method by which the Australian Bureau of Statistics (ABS) used data from the 2011 Census of Population and Housing and Census Post Enumeration Survey (PES) to produce final rebased estimates of the Aboriginal and Torres Strait Islander population for 30 June 2011.


THE CENSUS POST ENUMERATION SURVEY

2 While every effort is made to ensure full coverage of people and dwellings in Australia in the Census, small numbers of people will inevitably have been missed while others will have been counted more than once. In Australia more people are missed from the Census than are counted more than once. The net effect of overcount and undercount is called net undercount.

3 To measure net undercount of the Australian population, the ABS conducts the PES shortly after the Census. The PES is a sample survey that provides an independent check of Census coverage. In 2011, the survey had a sample of around 43,000 dwellings (with approximately 97,000 responding persons). In PES processing, the survey information from the PES dwelling is matched against corresponding Census forms for either the same Census dwelling, or for a dwelling nominated by the PES respondent as a likely address the would have been enumerated at, to determine whether each resident of the PES dwelling was counted in the Census. The PES also provides information about the consistency of data across the two collections.

4 The 2011 PES introduced several methodological changes including expanding the sample and to include more discrete Indigenous communities and over sampling in urban and regional areas with a high proportion of Aboriginal and Torres Strait Islander residents. Another significant changes was the implementation of Automated Data Linkage to improve the quality of matching between PES and Census records.

5 For more details on the PES, see Census of Population and Housing - Details of Undercount, 2011 (cat. no. 2940.0).


Net undercount

6 The PES estimate of the Aboriginal and Torres Strait Islander population at the time of the 2011 Census was 662,300 people. This compares with the Census count for Australia (excluding Other Territories) of 548,100 Aboriginal and Torres Strait Islander people. It is important to note that this Census count of Aboriginal and Torres Strait Islander people excludes people whose Indigenous status was unknown in the Census (see below). The Aboriginal and Torres Strait Islander net undercount (the difference between the PES Aboriginal and Torres Strait Islander population estimate and the actual Aboriginal and Torres Strait Islander population Census count) was 114,200 persons, 17.2% of the population.


Unknown Indigenous status

7 There were 1,059,000 Census records (4.9% of the total Census count) with unknown Indigenous status in the 2011 Census. Of these, 27.4% (or 1.3% of the total Census count) were a result of item non-response; that is, the ABS received a partially completed Census form for the person with the Indigenous status question unanswered. The remaining and majority (72.6%) of records with unknown Indigenous status (3.5% of the total Census count) were a result of imputation by the ABS for people who were identified as resident in dwellings (both private and non-private) at the time of the Census but for whom no Census form was received. While some of the records with unknown Indigenous status will be for people of Aboriginal and/or Torres Strait Islander origin and others for non-Indigenous people, no imputation was made for Indigenous status on the Census file. For a detailed discussion of unknown Indigenous status in the 2006 Census see Commentary: Interpreting The Data in the ABS publication Population Distribution, Aboriginal and Torres Strait Islander Australians, 2006 (cat. no. 4705.0). A discussion of unknown Indigenous status in the 2011 Census will be available in Census of Population and Housing: Understanding the Increase in Aboriginal and Torres Strait Islander Counts Between 2006 and 2011 (cat. no. 2077.0), due for release on 17 September 2013.

8 The PES estimated that of the 1,059,000 Census records with an unknown Indigenous status, about 28,400 were Aboriginal and/or Torres Strait Islander people.


CALCULATING ESTIMATED RESIDENT POPULATION - FINAL

Empirical Bayes method

9 Given the relatively high standard errors for net undercount by Indigenous status by state, the ABS used the Empirical Bayes estimation method to estimate more reliable undercount inputs for use in deriving population estimates. The Empirical Bayes method takes the original PES undercount estimate (the ratio of the PES population estimate to the Census count) for each region and smooths this towards a prediction based on the Census characteristics of the region (specifically the proportion of Aboriginal and Torres Strait Islander persons and the level of Census non-response in the region).

10 The Empirical Bayes method used for the 2011 estimates was largely the same as that used in 2006, except for some minor changes, including the use of 18 regions (up from 15 in 2006) to include a Northern Australia dimension.

11 The overall amount of smoothing used in each region was determined by two factors: the standard error for each region and an overall smoothing constant. The smoothing constant was chosen using the 'method of moments' technique developed by Morris (1983). The aim of smoothing is to provide stable estimates with lower standard errors. Regions with high standard errors required more smoothing and hence received a greater proportion of the national PES estimate, while regions with lower standard errors received a greater proportion of their individual PES estimate. The outcome of this methodology, in relation to smaller standard errors and confidence intervals, is presented in the table and graphs below.

Empirical Bayes Estimates and Standard Errors

EB Population Estimate
EB Undercount
SE
EB Undercount rate
SE
no.
no.
no.
%
%

New South Wales
205 762
33 147
6 743
16
2.7
Victoria
46 726
8 739
2 115
19
3.7
Queensland
187 223
31 402
6 022
17
2.7
South Australia
37 096
6 664
1 092
18
2.4
Western Australia
87 104
17 440
2 673
20
2.5
Tasmania
24 001
4 381
832
18
2.9
Northern Territory
68 346
11 561
1 849
17
2.2
Australian Capital Territory
6 068
884
233
15
3.2
Australia
662 326
114 218
14 274
17
1.8



12 Estimates of the Aboriginal and Torres Strait Islander (and non-Indigenous) population were then adjusted to include Australian residents temporarily overseas at the time of the Census (9 August 2011) and backdated to the estimated resident population reference date of 30 June 2011 using data on births, deaths, and interstate and overseas migration. Estimates were also assumed for net undercount in Other Territories, which were added to the Census count of Aboriginal and Torres Strait Islander people identified as being usually resident in those territories. At the national level, this resulted in a net increase of 7,500 from the 2011 PES estimate of 662,300 Aboriginal and Torres Strait Islander people (excluding Other Territories) at 9 August 2011 to the final estimate of the resident Aboriginal and Torres Strait Islander population at 30 June 2011 of 669,900 (including Other Territories).

13 The table below shows preliminary and final estimates as well as 2006 Census-based projections of the Aboriginal and Torres Strait Islander population, for 30 June 2011. For Australia, the final estimate is around 150 persons higher than the preliminary estimate (published on 27 September 2012 in Australian Demographic Statistics (cat. no. 3101.0).

Aboriginal and Torres Strait Islander ERP, State/Territory, preliminary and final rebased - 30 June 2011

Aboriginal and Torres Strait Islander ERP
Aboriginal and Torres Strait Islander population projections
Preliminary
Final
Difference
Low series(a)
High series(a)
no.
no.
no.
%
no.
no.

New South Wales
208 364
208 476
112
0.05
168 583
168 773
Victoria
47 327
47 333
6
0.01
37 603
37 647
Queensland
188 892
188 954
62
0.03
164 694
164 883
South Australia
37 392
37 408
16
0.04
31 005
31 040
Western Australia
88 277
88 270
-7
-0.01
77 607
77 694
Tasmania
24 155
24 165
10
0.04
20 551
20 580
Northern Territory
68 901
68 850
-51
-0.07
69 756
69 855
Australian Capital Territory
6 167
6 160
-7
-0.11
4 822
4 825
Australia(b)
669 736
669 881
145
0.02
574 874
575 552

(a) Projected Aboriginal and Torres Strait Islander population at 30 June 2011, based on 2006 Census.
(b) Includes Other Territories.


14 The final Aboriginal and Torres Strait Islander population estimate for 30 June 2011 (669,900 persons) was higher than the 9 August 2011 Census count (548,400 persons). This difference (22.2% or 121,500 people) represents the combined and net effects of Census net undercount (including people whose Indigenous status was unknown in the Census), residents temporarily overseas on Census night, demographic adjustments, and backdating to 30 June. The highest proportional increases from Census counts to final estimates were in WA (up 26.7%) and Victoria (up 24.6%).


Sub-state/territory Aboriginal and Torres Strait Islander estimates

15 The PES is the best available data source for determining what the Aboriginal and Torres Strait Islander population should have been on Census night, if the complete population was counted. However, as standard errors on the PES are too high for reliable estimates of the Aboriginal and Torres Strait Islander population to be produced at sub-state/territory levels, Census is the only data source for calculating estimates of the Aboriginal and Torres Strait Islander population for geographic areas smaller than a state or territory.

16 In producing estimates of the Aboriginal and Torres Strait Islander and non-Indigenous populations of Statistical Areas Level 2, PES estimates produced by the Empirical Bayes method for each state/territory were used as upper level constraints on the SA2-level Aboriginal and Torres Strait Islander populations as at Census night. State/territory net undercount was distributed pro-rata to individual SA2s, having regard to capital city/balance of state undercount for the total population according to their demographic characteristics such as age and sex.

17 It is important to note that at the sub-state/territory level, differences between Census counts and estimates of the Aboriginal and Torres Strait Islander population should not be interpreted as a definitive measure of the actual level of undercount; rather, these differences are a by-product of the assumptions that contribute to the estimation process and the differences should be considered indicative, based on the best available (though limited) information.


Plans for further output

18 A time series of Aboriginal and Torres Strait Islander population estimates and projections is scheduled for release in April 2014 in Estimates and Projections, Aboriginal and Torres Strait Islander Australians, 2001 to 2026 (cat. no. 3238.0).


FURTHER INFORMATION

19 Related ABS publications and references that may be of interest to users of this product include:

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