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EXPLANATORY NOTES


INTRODUCTION

1 For Australia, this publication contains estimates of the resident population of Local Government Areas (LGAs), Statistical Divisions (SDs), Statistical Districts, states and territories, Remoteness Areas and Australia. For the Northern Territory and Australian Capital Territory, estimates of the resident population are also provided for Statistical Subdivisions (SSDs). Estimates for all Statistical Local Areas (SLAs) and SSDs in Australia are available from the ABS web site in the electronic products that accompany this release.

2 To meet the conflicting demands for accuracy and timeliness there are several versions of sub-state/territory population estimates. Preliminary estimates are normally available eight months after the reference date (i.e. February), revised estimates a year later and final estimates after the following census. The population estimates in this publication are final for 2001, revised for 2005 (denoted 2005r) and preliminary for 2006 (denoted 2006p). The first series of population estimates based on the 2006 Census will be released in July 2007.

ESTIMATED RESIDENT POPULATION - AUSTRALIA

3 Estimated resident populations (ERPs) are official estimates of the Australian population, which link people to a place of usual residence within Australia. Usual residence is that place where each person has lived or intends to live for six months or more from the reference date for data collection.

4 Estimates of the resident population are based on census counts by place of usual residence (excluding overseas visitors in Australia), with an allowance for net census undercount, to which are added the number of Australian residents estimated to have been temporarily overseas at the time of the census.

5 Population estimates for Australia and the states and territories are updated by adding to the estimated population at the beginning of each period the components of natural increase (births minus deaths, on a usual residence basis) and net overseas migration. For the states and territories, account is also taken of estimated interstate movements involving a change of usual residence.

6 After each census, estimates for the preceding intercensal period are finalised by incorporating an additional adjustment (intercensal discrepancy) to ensure that the difference between the ERPs at the two respective census dates agrees with the total intercensal change.

7 A more detailed explanation of the concept of ERP, as adopted by the ABS for official population estimates, is contained in Demographic Estimates and Projections: Concepts, Sources and Methods (cat. no. 3228.0), ABS web site <www.abs.gov.au>.

ESTIMATION OF SLA-BASED POPULATIONS

8 In Australia, the SLA is the base spatial unit used to collect and disseminate statistics other than those collected from the Population Censuses. In non-census years, the SLA is the smallest unit defined in the Australian Standard Geographical Classification (ASGC). In aggregate, SLAs cover the whole of Australia without gaps or overlaps. Populations for SLAs are estimated as at 30 June each year. Population estimates for LGAs and other regions are built up from SLA-level estimates.

9 The ERP as at census date for each SLA is calculated based on usual residence census counts, excluding overseas visitors in Australia, with an allowance for net census undercount and the number of residents temporarily overseas at the census date. The estimates of net undercount are apportioned to SLAs based on age, sex, Indigenous status, state and territory, and (for the six states) capital city/balance of state. The number of residents temporarily overseas on census night is estimated based on coding addresses of residence to SLA from a sample of incoming passenger cards. As the census is held on a date other than 30 June (the 2001 Census was held on 7 August), further adjustments taking into account births, deaths and migration for the intervening period are made to obtain the ERP at 30 June.

10 For post-censal years, the absence of migration data at the SLA level means that it is not possible to estimate SLA populations by taking into account natural increase and net migration. Instead, these ERPs are calculated using a mathematical model, where relationships are established between changes in population and changes in indicators between the two most recent censuses for groups of SLAs. The choice of indicators varies across the states and territories, depending on availability and indicative ability, and includes dwelling approvals, electricity connections, Medicare enrolments and drivers’ licences. The choice of indicators also varies within states/territories, depending on aspects such as whether the SLA is urban or rural, and is growing or declining. Changes in these indicators are then used to estimate changes in the population of each area since the last census. In some areas population change since the previous census is assumed to be zero in the absence of reliable indicator data for these areas.

11 All output from the model is scrutinised and validated by population analysts. Local knowledge, including that advised by local governments, may be used to adjust the outcome of the model for a particular SLA. Estimates at SLA level are constrained to state/territory population estimates.

12 There was a break in series between Medicare enrolments data provided to the ABS used to model the preliminary 30 June 2005 SLA populations, and enrolments data provided in previous years. Initial advice received from Medicare Australia indicated that this was due to new business rules applied to Medicare enrolments data from February 2005. Based on further information received from Medicare Australia throughout 2006, the ABS was able to determine the effect of these changes on preliminary 2005 ERP for particular areas. As a result, there were several revisions made to the 2005 SLA-based population estimates, which affected some areas more than others. These revised 2005 population estimates are incorporated in this issue.

13 Due to the unreliability of post-2004 indicator data for the Queensland SLAs of Mornington (S) and Aurukun (S), ERPs for these areas will be held constant from June 2004 until the 2006 Census-based ERPs are available.

ESTIMATION OF SUB-SLA POPULATIONS

14 Census Collection Districts (CDs) are designed for use in census years for the collection and dissemination of Population Census data. In aggregate, CDs cover the whole of Australia without gaps or overlaps. In census years, one or more CDs form an SLA.

15 To provide some indication of estimated resident population below the SLA level, the ABS prepares population estimates for CDs. These estimates are aggregated to form population estimates for regions such as Remoteness Areas, and are used in the calculations of population estimates for several SLAs created since the 2001 Census.

16 Final population estimates at the CD level as at 30 June of a census year are compiled by apportioning the population estimate for each SLA across the CDs within the SLA, using census usual residence counts. In subsequent years, the 30 June population estimates for SLAs are apportioned across CDs by taking into account population change implied by new dwelling approvals in each CD since the census year. For SLAs involved in boundary changes, each CD is assigned to one or more SLAs, and for CDs which fall within more than one SLA an estimate is made of the split of the CD's population and dwellings across SLAs. The CD populations within each SLA are then adjusted (on a pro-rata basis) to add to the SLA population.

17 There are some limitations to this approach. For instance, the SLA to CD level apportionment assumes that net undercount is distributed to component CDs in proportion to the census usual residence counts. It is quite possible that there may be local clustering and regional differences in net undercount which cannot be practically or efficiently measured. Similarly, the process of apportioning the number of residents temporarily overseas on census night from SLA to CD assumes these are distributed to CDs in proportion to the census usual counts. Births, deaths and migration data are not available by CD between 30 June and the census date and are therefore implicitly estimated when backdating the census date estimate to the 30 June reference date.

ACCURACY OF SLA-BASED POPULATION ESTIMATES

18 In census years, both preliminary estimates (derived from updating the ERPs from the previous census) and final estimates (based on the current census) are prepared. Differences between these two sets of estimates are referred to as intercensal errors. An indication of the accuracy of ERPs can be gauged by assessing the size and direction of the intercensal errors. For Australia, the preliminary June 2001 ERP under-estimated the final June 2001 ERP by 0.1% (-26,600 persons). For the states/territories, the 2001 intercensal errors ranged from -1.6% (Australian Capital Territory) to +0.5% (Victoria).

19 Summary statistics of the absolute values of these errors can be used to assess a number of population estimates. The average absolute value of the intercensal errors for the 2001 series of SLA estimates (excluding regions with an ERP less than 500) was 3.8%, a decrease on the 1996 average of 4.6%. For LGAs, the 2001 average absolute intercensal error (excluding regions with an ERP less than 500) was 3.6%, an increase on the 1996 average of 3.4%.

20 Average absolute intercensal errors for the 2001 series of LGA estimates decreased with increasing population size; that is, LGAs with large populations recorded the smallest percentage errors while small LGAs recorded the largest percentage errors.

Average absolute intercensal error, Australia - 30 June 2001
	Number of LGAs	Average absolute intercensal error
Size of LGA (people)	no.	%
Under 500	21	10.5
500 to 1,999	93	7.7
2,000 to 4,999	109	4.4
5,000 to 9,999	91	3.8
10,000 to 19,999	94	2.7
20,000 to 49,999	100	2.0
50,000 and over	116	1.5

INTERPRETATION OF LGA RANKINGS

22 In Tables 1 to 7 LGAs are ranked within states and territories according to both ‘largest’ and ‘fastest’ preliminary growth, identifying areas in Australia currently experiencing significant changes in population size. Largest growth is based on the absolute change in population between June 2005 and June 2006, while fastest growth is based on the rate of change in population (that is, the percentage change in population) for the same period. LGAs with populations of less than 2,000 people at June 2005 have been excluded from the fastest growth rankings.

23 Due to the inherent imprecision of small-area population estimates, rankings should be considered indicative of relative growth between LGAs within each state and territory, not definitive.

AVERAGE ANNUAL RATE OF GROWTH

24 The average annual growth rate is calculated as a percentage using the formula below, where P0 is the population at the start of the period, Pn is the population at the end of the period and n is the length of the period between Pn and P0 in years.

26 The 2001 CD level estimates, or aggregations of these, were used to estimate the populations for these new SLAs as at 30 June 2001. In some cases where SLA boundaries do not correspond directly to 2001 Census CD boundaries, estimates were made as to the share of population to be allocated from the CD to each relevant SLA, and added to the SLA accordingly. Estimates for 30 June 1996 were prepared similarly. The census year population estimates for these SLAs based on CD level apportionment are deemed to be reasonable approximations in the absence of finer level components.

27 At the present time the ABS has not been able to identify any data sources that can yield reliable and comprehensive information on annual population change for these areas. The small size and remoteness of some of these areas means that postcode address-based data sets are of limited use. The nature of postal delivery areas and the prevalent use of post box-based addresses (which may not be a clear indication of place of residence) in some of these areas limit the utility of postcode-based data to estimate population change for these areas. While additional administrative data and local knowledge was used to estimate for population change from 30 June 2001 to 2002 for the Queensland areas, significant changes occurred in these data sources which limited their suitability for estimating population change for these SLAs from 2002 onwards. Small populations are relatively more sensitive to small population changes which may not be detectable or quantifiable; larger populations contain much of this variability within the larger population.

28 The ABS has therefore not been able to estimate population change for these new SLAs in the Northern Territory and South Australia since 30 June 2001, nor for these new SLAs in Queensland since 30 June 2002. Population estimates for these SLAs for periods between 1996 and 2001 have been prepared using interpolation techniques between the 1996 and 2001 census year estimates. The ABS plans to use these techniques for preparing interpolated estimates for years between 2001 and 2006 after the 2006 census-based estimates become available.

29 Where the ABS has not been able to estimate annual population change, estimates in this publication have been represented as "np". In the calculation of these population estimates, the most recently prepared estimates (30 June 2002 for the Queensland areas, and 30 June 2001 for the Northern Territory and South Australia areas) have been held constant to June 2006 to ensure individual estimates sum to totals. The most recently prepared estimates for these areas are contained in the accompanying electronic release of this product. Although these estimates indicate no change in population over this period, it should not be assumed that this is the case. Because SLA-level population estimates are constrained to predetermined state/territory estimates, the population estimates for the remainder of these states/territories may be slightly affected. For example, if the population in these Indigenous Council areas actually increased, then the population of the remaining areas will be, overall, slightly overestimated.

30 For the time being, and in the absence of other reliable data sources, the ABS may only be able to produce population estimates for these SLAs in census years using data from the five-yearly census. The ABS will continue to monitor the availability of other data sources for population change estimation in consultation with state, territory and local governments. For example, the inclusion of these areas in the ASGC means that other data such as births and deaths by place of usual residence can be coded to these new geographic levels for potential future use in small area population estimation.

SERVICE POPULATIONS

31 Service population estimates are a different measure of population. They take into account seasonal and itinerant populations which are not included in the ERP. Currently the ABS does not produce service population estimates but two working papers are available on the ABS web site <www.abs.gov.au> which investigate the concept and feasibility of such estimates: Demography Working Paper 1996/4 - When ERPs aren't Enough (cat. no. 3112.0) and Demography Working Paper 1999/3 - Service Population Pilot Study: An Investigation to Assess the Feasibility of Producing Service Population Estimates for Selected LGAs (cat. no. 3117.0).

ESTIMATED RESIDENT POPULATION - NEW ZEALAND

32 Population estimates for New Zealand (NZ) are no longer included in this publication. Subnational population estimates and other population data for NZ are now freely available from the Statistics New Zealand web site <www.stats.gov.nz>.

AUSTRALIAN STATISTICAL AREAS

33 This publication contains data presented according to the 2006 edition of the Australian Standard Geographical Classification (ASGC), which refers to boundaries as defined at 1 July 2006. Under this classification, statistical areas are defined as follows:

• Local Government Areas (LGAs). These areas are the spatial units which represent the geographical areas of incorporated local government councils. The ABS has broadened the categories of legislation used to define local government areas for statistical purposes to include the Indigenous Council areas in the states and Northern Territory. The LGA Structure covers only incorporated areas of Australia, which are legally designated parts of states and territories over which incorporated local governing bodies have responsibility.
• Statistical Local Areas (SLAs). These areas are, in most cases, identical with, or have been formed from a division of, whole LGAs. In other cases they represent unincorporated areas. In aggregate, SLAs cover the whole of a state or territory without gaps or overlaps. In some cases legal LGAs overlap Statistical Subdivision boundaries and therefore comprise two or three SLAs (Part A, Part B and, if necessary, Part C).
• Statistical Subdivisions (SSDs). These are of intermediate size, between SLAs and SDs. In aggregate, they cover the whole of Australia without gaps or overlaps. They are defined as socially and economically homogeneous regions characterised by identifiable links between the inhabitants. In the non-urban areas an SSD is characterised by identifiable links between the economic units within the region, under the unifying influence of one or more major towns or cities.
• Statistical Divisions (SDs). These consist of one or more SSDs. The divisions are designed to be relatively homogeneous regions characterised by identifiable social and economic units within the region, under the unifying influence of one or more major towns or cities. There were some major changes made to the SD structure in south-east Queensland in the 2006 edition of the ASGC.
• Statistical Districts. These consist of selected, significant, predominantly urban areas in Australia which are not located within a Capital City SD. Statistical Districts enable comparable statistics to be produced about these selected urban areas.

35 The Remoteness Structure is defined only in census years and its purpose is to classify CDs which share common characteristics of remoteness into these broad geographical regions. The criteria defining RAs are based on the Accessibility/Remoteness Index of Australia (ARIA) which measures the remoteness of a point based on the physical road distance to the nearest Urban Centre (ASGC 1996) in each of five size classes. Characteristics of remoteness are determined in the context of Australia as a whole and therefore not all RAs are represented in each state/territory. For more information on the Remoteness Structure see Australian Standard Geographical Classification, 2001 (cat. no. 1216.0).

36 Further information concerning statistical areas is contained in Australian Standard Geographical Classification, 2006 (cat. no. 1216.0).

CALCULATION OF AREAS

37 The area figures used in this issue are based upon the SLA level of the Australian Standard Geographical Classification, 2006 edition. The areas of the SLAs were calculated using ABS standard Geographic Information Systems software from the digital boundaries of this ASGC edition. Higher level spatial unit area figures are aggregations of the relevant SLA areas. The area of each SLA is included in the SLA spreadsheets accompanying this publication.

MAPS

38 A complete series of SLA maps is available in Australian Standard Geographical Classification, 2006 (cat. no. 1216.0).

39 The centre of population is one measure used to describe the spatial distribution of a population. The method of calculation used in this publication for the map on page 10 is based on the ‘centroid’ (i.e. centre) and population of each SLA in Australia. Latitude and longitude coordinates of the centroid of each SLA are multiplied by the SLA’s estimated resident population to obtain weighted latitudes and longitudes. These are summed to obtain a weighted latitude and longitude coordinate for all Australia, then divided by the total population of Australia to obtain a single latitude and longitude coordinate, the centre of population.

40 Due to the inherent imprecision in small area estimates, and the choice of SLA-level estimates in the above calculation (rather than estimates at a different geographical level, for example, the Census Collection District or Local Government Area level), the centre of population should be considered indicative only of the distribution of population, and cannot be ascribed to an exact location. Use of different geographical level data would result in a slightly different centre of population.

ELECTRONIC DATA

41 Annual population estimates at 30 June for all SLAs and LGAs in Australia are available electronically. This information can be customised to provide data for any choice of years and any combination of states and territories. Electronic copies of this publication (in .pdf format), plus current and earlier year estimates for all SLAs and LGAs in Australia, are freely available from the ABS web site <www.abs.gov.au>.

ACKNOWLEDGMENT

42 ABS publications draw extensively on information provided freely by individuals, businesses, governments and other organisations. Their continued cooperation is very much appreciated; without it, the wide range of statistics published by the ABS would not be available. Information received by the ABS is treated in strict confidence as required by the Census and Statistics Act 1905.

RELATED RELEASES

43 Other ABS releases that are freely available on the ABS web site <www.abs.gov.au> and may be of interest to users of this publication include:

Australian Demographic Statistics (cat. no. 3101.0)
Australian Historical Population Statistics (cat. no. 3105.0.65.001)
Australian Standard Geographical Classification (ASGC), 2006 (cat. no. 1216.0)
Births, Australia (cat. no. 3301.0) - SLA-specific datasets
Census of Population and Housing: Population Growth and Distribution, Australia, 2001 (cat. no. 2035.0)
Deaths, Australia (cat. no. 3302.0) - SLA-specific datasets
Population by Age and Sex (cat. no. 3235.0-8.55.001) - state and territory-specific datasets
Population by Age and Sex, Australian States and Territories (cat. no. 3201.0)
Regional Statistics - regional statistics available on the ABS home page

45 Current publications and other products released by the ABS are listed in the Catalogue of Publications and Products (cat. no. 1101.0). The Catalogue is available from any ABS office or the ABS web site <www.abs.gov.au>. The ABS also issues a daily Release Advice on the web site which details products to be released in the week ahead.

46 As well as the statistics included in this and related publications, additional information is available from the ABS web site <www.abs.gov.au> by selecting Themes then Demography.