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FEATURE ARTICLE 2: INDIGENOUS ESTIMATED RESIDENT POPULATION — METHOD OF CALCULATION


INTRODUCTION

Estimated resident population (ERP) is the official measure of the population of Australia and the states and territories. Among other purposes, these estimates are used for determining the number of seats in the House of Representatives for each state and territory, and for the allocation of government funding. Estimated resident population is derived from the Census and from other sources of information including the Census Post Enumeration Survey (PES).

In addition to estimated resident population for the total population, the ABS produces estimated resident population by Indigenous status with the following categories:

• Aboriginal origin only
• Torres Strait Islander origin only
• Both Aboriginal and Torres Strait Islander origin
• non-Indigenous.

THE CENSUS POST ENUMERATION SURVEY

While every effort is made to ensure full coverage of people and dwellings in Australia in the Census, inevitably small numbers of people will 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.

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 2006, the survey had a sample of around 40,000 private dwellings (approximately 88,200 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 Census night address, to determine whether each resident of the PES household was counted in the Census. The PES also provides information about the consistency of data across the two collections.

The 2006 PES introduced several methodological changes including extending the scope of the survey to remote areas of Australia and discrete Indigenous communities. A new estimation method was also introduced. For more details on the PES, see Information Paper: Measuring Net Undercount in the 2006 Population Census, 2007 (cat. no. 2940.0.55.001); Census of Population and Housing - Undercount, August 2006 (cat. no. 2940) released 5 June 2007 and Census of Population and Housing - Details of Undercount, August 2006 (cat. no. 2940) released 31 August 2007.

Net undercount

The PES estimate of the Indigenous population at the time of the 2006 Census was 514,000 people. This compares with the Census count for Australia (excluding Other Territories) of 454,800 Indigenous people. This Census count of Indigenous people excludes people whose Indigenous status was unknown in the Census (see below). The Indigenous net undercount (the difference between the PES Indigenous population estimate and the actual Indigenous population Census count) was 59,200 persons.

Net undercount by Indigenous status(a) - 2006
	PES estimate(b)	Census count	Net undercount(c)
Indigenous status	no.	no.	no.
Indigenous	513 977	454 799	59 178
Non-Indigenous	19 888 482	18 264 880	1 623 602
Not stated	. .	1 133 294(d)	. .
Total	20 402 459	19 852 973	549 486
. . not applicable
(a) Excludes Other Territories. Other Territories were not in scope of the 2006 PES.
(b) PES estimates of the population that should have been counted in the 2006 Census.
(c) Difference between PES estimate and Census count.
(d) Census records where Indigenous status was unknown because the Census form was not received or only partially completed.

UNKNOWN INDIGENOUS STATUS

There were 1,133,300 Census records (5.7% of the total Census count) with unknown Indigenous status in the 2006 Census. Of these, 29% were a result of item non-response, that is, the ABS received a partially completed Census form for the person but with the Indigenous status question unanswered. This resulted in an item non-response rate of 1.7%. The remaining and majority (71%) of records with unknown Indigenous status (4.1% 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 Chapter 2: Interpreting the data in the ABS publication Population Distribution, Aboriginal and Torres Strait Islander Australians (cat. no. 4705.0).

CALCULATING ESTIMATED RESIDENT POPULATION (ERP)

The estimated resident population for Australia, states and territories by age and sex, and by Indigenous status are compiled using the Census, PES and other demographic information.

The Census provides detailed information on the age and sex structure, and location of the population, but it misses some people who should have been counted in the Census. In addition, while Census records with unknown Indigenous status remain not stated on the Census file, for the purposes of population estimation they are allocated to either Indigenous or non-Indigenous according to the distribution of stated responses within each age group, sex, Census form type and geographic area (Statistical Local Area).

The PES produces direct estimates of the number of people who should have been counted in the Census by selected variables (state and territory, part of state, sex, age group, country of birth, and Indigenous status). For the Indigenous population, direct PES estimates for individual jurisdictions are used where sample size is sufficient; in other cases, jurisdictions have had to be grouped for ERP purposes. Some minor demographic adjustments (designed to address any anomalies in age and sex composition) were also made to Census counts in producing ERP.

PES estimates of net undercount for Indigenous persons in the 2006 Census were used at the national level and for five jurisdictional groups. These were:

• New South Wales/Australian Capital Territory
• Victoria/South Australia/Tasmania
• Queensland
• Western Australia
• Northern Territory

The PES estimates provided upper level constraints on the Indigenous populations of the five jurisdictional groups, and net undercount was distributed to individual states/territories by synthetic estimation, having regard to capital city/balance of state undercount for the total population by age and sex.

Indigenous net undercount by state/territory - 2006
	PES estimate(a)
	Persons	Standard Error (SE)	Relative Standard Error (RSE)	Usual residence Census count	Net undercount	Net undercount rate(b)
State/territory groups	no.	no.	%	no.	no.	%
New South Wales/Australian Capital Territory	151 048	9 146	6.1	142 382	8 666	5.7
Victoria/South Australia/Tasmania	73 380	4 337	5.9	72 467	913	1.2
Queensland	145 843	6 087	4.2	127 580	18 263	12.5
Western Australia	77 304	5 605	7.3	58 710	18 594	24.1
Northern Territory	66 402	2 341	3.5	53 661	12 741	19.2
Australia(c)	513 977	13 309	2.6	454 799	59 178	11.5
(a) PES estimate of the Indigenous population that should have been counted in the 2006 Census.
(b) Net undercount as a percentage of the PES estimate.
(c) Excludes Other Territories. Other Territories were not in scope of the 2006 PES.

Estimates of the Indigenous (and non-Indigenous) population were adjusted to include Australian residents temporarily overseas at the time of the Census in August 2006 and backdated to the estimated resident population reference date of 30 June 2006 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 Indigenous people identified as being usually resident in those territories. At a national level, this resulted in a net increase of 3,200 from the 2006 PES estimate of 514,000 Indigenous people (excluding Other Territories) at August 2006 to the preliminary estimate of the resident Indigenous population at 30 June 2006 of 517,200 (including Other Territories).

The Indigenous ERP for 30 June 2006 (517,200 persons) was higher than the August Census count (455,000). This difference (up 13.7% or 62,100 persons) 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 count to ERP were in Western Australia (up 32.7%) and the Northern Territory (up 24.1%). Preliminary estimates by state/territory for the four categories of Indigenous status (Aboriginal origin only, Torres Strait Islander origin only, Both Aboriginal and Torres Strait Islander origin, and non-Indigenous) are presented in table 1 of Population Distribution, Aboriginal and Torres Strait Islander Australians (cat. no. 4705.0)

Comparison of Census, PES and ERP, Indigenous population - 2006
	Usual residence Census count, August 2006	PES estimate, August 2006(a)	Indigenous ERP, 30 June 2006(b)	Difference between ERP and Census count	Percentage increase from Census count(c)
State/Territory	no.	no.	no.	no.	%
New South Wales	138 507	. .	148 178	9 670	7.0
Australian Capital Territory	3 875	. .	4 043	169	4.4
New South Wales/Australian Capital Territory	142 382	151 048	152 221	9 839	6.9
Victoria	30 143	. .	30 839	696	2.3
South Australia	25 556	. .	26 044	488	1.9
Tasmania	16 768	. .	16 900	132	0.8
Victoria/South Australia/Tasmania	72 467	73 380	73 783	1 316	1.8
Queensland	127 580	145 843	146 429	18 849	14.8
Western Australia	58 710	77 304	77 928	19 218	32.7
Northern Territory	53 661	66 402	66 582	12 921	24.1
Australia(d)	455 028	(e)513 977	517 174	62 146	13.7
. . not applicable
(a) PES estimate of the Indigenous population that should have been counted in the 2006 Census.
(b) Preliminary.
(c) The Census count is used as the denominator in this table whereas the PES population estimate is used as the denominator for the net undercount rate.
(d) Includes Other Territories unless otherwise stated.
(e) Excludes Other Territories. Other Territories were not in scope of the 2006 PES.

Plans for further output

Final resident population estimates by Indigenous status will be available in mid 2008 and released in a datacube spreadsheet (cat. no. 3238.0.55.001) on the ABS web site <www.abs.gov.au>. The datacube will present estimates at sub-state levels of geography. Requests for preliminary estimates of Indigenous population for sub state/territory geographic levels may be directed to Phil Browning on (02) 6252 6639 or e-mail demography@abs.gov.au. A time-series of Indigenous population estimates and projections will be released in August 2009 in Experimental Estimates and Projections, Aboriginal and Torres Strait Islander Australians, 1996 to 2016 (cat. no. 3238.0). This publication will also present an analysis of components of growth in the Indigenous population between 2001 and 2006.

Further reading:

Census of Population and Housing - Undercount, 2006 (cat. no. 2940.0)

Information Paper: Measuring Net Undercount in the 2006 Population Census, 2007 (cat. no. 2940.0.55.001)

Australian Demographic Statistics Quarterly (cat. no. 3101.0)

Research Paper: An Estimating Equation Approach to Census Coverage Adjustment, May 2007 (cat. no. 1351.0.55.019)

Demographic Estimates and Projections: Concepts sources and methods, 1999 (cat. no. 3228.0)

Occasional Paper: Population Issues, Indigenous Australians, 1996 (cat. no. 4708.0)