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TECHNICAL NOTE 1 MEASURING CHANGE IN POPULATION ESTIMATES OF ABORIGINAL AND TORRES STRAIT ISLANDER PEOPLES
MEASURABLE COMPONENTS OF CHANGE IN POPULATION ESTIMATES OF ABORIGINAL AND TORRES STRAIT ISLANDER PEOPLES
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
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
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
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