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2077.0 - Census of Population and Housing: Understanding the Increase in Aboriginal and Torres Strait Islander Counts, 2006-2011 Quality Declaration 
Latest ISSUE Released at 11:30 AM (CANBERRA TIME) 17/09/2013  First Issue
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TECHNICAL NOTE 1 MEASURING CHANGE IN POPULATION ESTIMATES OF ABORIGINAL AND TORRES STRAIT ISLANDER PEOPLES

POPULATION ESTIMATES

1 While each Census aims to count everyone in Australia on Census night, the size and scale of the data collection process make it inevitable that some people will be counted more than once, and some will not be counted at all. The combined effect of this is measured by the Post Enumeration Survey (PES), which historically always indicates that there has been a net undercount (that is, more people were missed than were counted more than once).

2 An adjustment for the net undercount and other factors is applied to the Census counts to produce population estimates. This adjustment process is particularly important for producing Aboriginal and Torres Strait Islander population estimates, because the number of Aboriginal and Torres Strait Islander people not counted in the Census is considerably higher than the number who are counted more than once, resulting in a relatively large net undercount.

3 The importance of changes in undercount is such that the analysis in this Technical Note specifically includes a population-estimates based analysis of the change in Census counts. The analysis mirrors that presented in Measuring Changes in Population between Censuses, but population estimates, not Census counts, are analysed. This provides a basis for also assessing the proportion of change that can reasonably be attributed to undercoverage and changes to PES methodology.

For the analysis of change in population estimates the following framework has been used:

    Population estimate 1
      + births registered between Census 1 and Census 2
      - deaths registered between Census 1 and Census 2
      +/- net migration between Census 1 and Census 2
      +/- the impact of measurable changes in Post Enumeration Survey (PES) methodology
      +/- the impact of measurable changes in Census coverage
      +/- the impact of factors which cannot be explained by measurable components of population change or changes in methodology or coverage
    = Population estimate 2


MEASURABLE COMPONENTS OF CHANGE IN POPULATION ESTIMATES OF ABORIGINAL AND TORRES STRAIT ISLANDER PEOPLES

Demographic factors

4 Analysis of the change in Census counts is limited by the fact that, unlike population estimates, adjustments are not made for undercount and any other factors (such as people temporarily overseas on Census night). For more detailed information about these adjustments, refer to Australian Demographic Statistics (cat. no. 3101.0). For this reason, population estimates are considered to be a more accurate reflection of the population than Census counts, and provide a more complete picture of ‘explainable' change.

5 Change attributable to demographic factors is presented here using estimated resident population (ERP) figures. It is important to note the data used in this analysis is based on registered births and deaths, rather than projected births and deaths. For more information, see the chapter Measuring Changes in Population between Censuses.

6 Analysis of the ‘demographic’ components of change in the estimated resident population reveals that a smaller percentage of the change observed in the population estimate of Aboriginal and Torres Strait Islander people between 2006 and 2011 is attributable to births, deaths and migration than was reflected in the analysis of the change in Census counts. This highlights the contribution of changes in Census undercount and the methodology used to measure undercount between the 2006 and 2011 Censuses, which are explored further in this chapter. It also reflects a change in the size of the adjustment for residents temporarily overseas which, given the relatively small impact, is not separately identified within this analysis.


CHANGE DUE TO DEMOGRAPHIC FACTORS, Aboriginal and Torres Strait Islander population, 2006-2011

Population estimate
Relative change
Relative change due to
demographic factors
2006
2011
2006-2011
Natural increase(a)
2006-2011
Overseas migration
2006-2011
Interstate migration
2006-2011
2006-2011
no.
no.
no.
%
no.
no.
no.
no.
%

New South Wales
152 685
208 476
55 791
36.5
18 056
411
-1 996
16 471
29.5
Victoria
33 517
47 333
13 816
41.2
4 629
174
833
5 636
40.8
Queensland
144 885
188 954
44 069
30.4
20 360
435
1 212
22 007
49.9
South Australia
28 055
37 408
9 353
33.3
3 732
57
326
4 115
44.0
Western Australia
70 966
88 270
17 304
24.4
9 356
172
294
9 822
56.8
Tasmania
18 415
24 165
5 750
31.2
1 810
37
-51
1 796
31.2
Northern Territory
64 005
68 850
4 845
7.6
5 582
44
-793
4 833
99.8
Australian Capital Territory
4 282
6 160
1 878
43.9
618
45
150
813
43.3
Australia(b)
517 043
669 881
152 838
29.6
64 160
1 375
. .
65 535
42.9

(a) Registered births minus registered deaths.
(b) Includes
Other Territories.
Note: Totals and components may not be consistent within and between tables due to introduced random error to protect confidentiality of Census respondents - see Census Dictionary, 2011 (cat. no. 2901.0).


Changes in Census undercount and the method used to calculate undercount

7 Applying estimates of net undercount from the PES to the Census counts is a major part of the calculation of the estimated resident population. While the above analysis of population change components provides important insight into the increase between the 2006 and 2011 Aboriginal and Torres Strait Islander population estimates, it is essential that any change analysis includes an estimate of the change in undercount over this period. It is also important to consider any measurable impact of a change in PES methodology, which will affect the comparability of undercount estimates over time.

8 Two key changes were made to the 2011 PES methodology which had an impact on the comparability of 2006 and 2011 net undercount figures for the Aboriginal and Torres Strait Islander population. The first of these changes was an improvement in the collection of Indigenous status in the PES and is likely to have had the greatest impact. A household-level question (used in 2006) was replaced with a person-level question in the 2011 PES. This meant that the Indigenous status question was collected for everyone in the dwelling on a person by person basis, resulting in identification in the 2011 PES that was more closely aligned with that in the Census. For more information on this change, refer to Technical Note 1: Improvement in Collection of Indigenous Status in Census of Population and Housing - Details of Undercount, 2011 (cat. no. 2940.0). Had this improved methodology been available in 2006, it is estimated that the net undercount of Aboriginal and Torres Strait Islander people in 2006 would have been much higher than the published 11.5%, and likely higher than the 2011 net undercount of 17.2%.

9 The second methodological change in the 2011 PES was the introduction of Automated Data Linking, which significantly improved the PES linking and matching methodology and, consequently, the net undercount estimates. If it had been possible to better match PES and Census records for Aboriginal and Torres Strait Islander people in 2006, this methodological change would have resulted in a small decrease in the net undercount in 2006, a small offset to the larger impact from the change in identification.

10 The challenge with estimating these impacts is the need to involve assumptions. Some assumptions have been required, given there is no possibility of repeating the collection of Indigenous status for the Census population in 2006, or of undertaking the linking and matching of 2006 PES and Census records since name and address information is destroyed at the conclusion of Census processing. This means that the ABS has produced its 'best estimate' of what the impact would have been in 2006, using the relationship in available data for the 2006 PES and 2011 PES. For this reason, these estimates should be considered illustrative of the impact of the change in PES methodology.

11 Almost one-quarter (23% or 35,600) of the 152,800 increase in the estimated Aboriginal and Torres Strait Islander population can be explained by changes in PES methodology, with a further 13% (19,500) reflecting an illustrative estimate of the change in the 'actual' Census undercount between 2006 and 2011. The combined effect of these changes was a net increase of 55,100 Aboriginal and Torres Strait Islander people between 2006 and 2011, which accounts for 36% of the increase in the population estimates between 2006 and 2011.


CHANGE IN POPULATION ESTIMATES ATTRIBUTABLE TO CHANGES IN CENSUS UNDERCOUNT AND METHOD USED TO CALCULATE UNDERCOUNT, 2006-2011

Population estimate
Relative change
Changes to PES methodology(a)
Other changes in undercount(b)
Relative change due to methodology and undercount
2006
2011
2006-2011
2006-2011
no.
no.
no.
%
no.
no.
no.
%

New South Wales
152 685
208 476
55 791
36.5
13 596
6 551
20 147
36.1
Victoria
33 517
47 333
13 816
41.2
3 810
1 805
5 615
40.6
Queensland
144 885
188 954
44 069
30.4
8 918
5 693
14 611
33.2
South Australia
28 055
37 408
9 353
33.3
3 198
1 068
4 266
45.6
Western Australia
70 966
88 270
17 304
24.4
3 036
2 744
5 780
33.4
Tasmania
18 415
24 165
5 750
31.2
2 123
638
2 761
48.0
Northern Territory
64 005
68 850
4 845
7.6
726
636
1 362
28.1
Australian Capital Territory
4 282
6 160
1 878
43.9
284
224
508
27.1
Australia(c)
517 043
669 881
152 838
29.6
35 608
19 451
55 059
36.0

(a) Estimated net impact of measurable changes to Post Enumeration Survey (PES) methodology (that is, improved collection of Indigenous status and the introduction of Automated Data Linking).
(b) Estimated change in undercount excluding the estimated impact of changes to PES methodology.
(c) Includes Other Territories.
Note: Totals and components may not be consistent within and between tables due to introduced random error to protect confidentiality of Census respondents - see Census Dictionary, 2011 (cat. no. 2901.0).


ERROR OF CLOSURE - POPULATION ESTIMATES OF ABORIGINAL AND TORRES STRAIT ISLANDER PEOPLES

12 Three-quarters (120,600) of the 152,700 increase in the estimated Aboriginal and Torres Strait Islander population between 2006 and 2011 can be attributed to known and measurable sources of population change, as well as the estimated impact of changes to PES methodology and Census coverage. The residual portion of the increase (32,200 people) represents 4.8% of the 2011 estimated resident population, slightly lower than the 6.1% error of closure observed when looking at the change in Census counts.


ERROR OF CLOSURE FOR ESTIMATED RESIDENT POPULATION, Aboriginal and Torres Strait Islander people, 2006-2011

Population estimate
Relative change
Total explainable increase(a)
Error of closure
2006
2011
2006-2011

2006-2011

no.
no.
no.
%
no.
%
no.
%

New South Wales
152 685
208 476
55 791
36.5
36 618
65.6
19 173
9.2
Victoria
33 517
47 333
13 816
41.2
11 251
81.4
2 565
5.4
Queensland
144 885
188 954
44 069
30.4
36 618
83.1
7 451
3.9
South Australia
28 055
37 408
9 353
33.3
8 381
89.6
972
2.6
Western Australia
70 966
88 270
17 304
24.4
15 602
90.2
1 702
1.9
Tasmania
18 415
24 165
5 750
31.2
4 557
79.3
1 193
4.9
Northern Territory
64 005
68 850
4 845
7.6
6 195
127.9
-1 350
-2.0
Australian Capital Territory
4 282
6 160
1 878
43.9
1 321
70.3
557
9.0
Australia(b)
517 043
669 881
152 838
29.6
120 594
78.9
32 244
4.8

(a) Change explainable due to births minus deaths, changes to Census processing, overseas and interstate migration and changes to Post Enumeration Survey (PES) methodology.
(b) Includes
Other Territories.
Note: Totals and components may not be consistent within and between tables due to introduced random error to protect confidentiality of Census respondents - see Census Dictionary, 2011 (cat. no. 2901.0).

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