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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 accompanying electronic release, Regional Population Growth, Australia, Electronic Delivery (cat. no. 3218.0.55.001).

2 To meet the conflicting demands for accuracy and timeliness there are three estimates of sub-state/territory populations. 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 2000, revised for 2004 (denoted 2004r) and preliminary for 2005 (denoted 2005p).

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, 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. 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. 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 In the model, a relationship is established between changes in population and changes in indicators between the two most recent censuses. 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, is growing or declining, and has a high or low proportion of medium- and high-density dwellings. Changes in these indicators are then used to estimate changes in the population of each area since the last census.

12 There is a break in series between Medicare enrolments data provided to the ABS in 2005 (used to model the 30 June 2005 SLA populations) and enrolments data provided in previous years. Advice received from Medicare Australia indicated that this is due to new business rules applied to Medicare enrolments data from February 2005. For the time being the ABS has been unable to precisely determine the effect of these changes on modelled ERP for particular areas, however the break in series was taken into account when validating modelled 2005 estimates. The ABS is working with Medicare Australia to determine whether some areas were affected more than others by these changes.

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 In census years, CD level population estimates are compiled by apportioning the 30 June 2001 ERP for each SLA to the CDs within each SLA, using 2001 Census usual residence counts. In post-census years, each CD is assigned to one SLA (for CDs which fall within more than one new SLA, the CD is assigned based on which SLA is deemed to contain the most population). The 30 June 2001 CD population estimate is then updated to reflect any extra population implied by new building approvals in the CD since 30 June 2001. 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’ growth, identifying areas in Australia currently experiencing significant changes in population size. Largest growth is based on the absolute change in population between June 2004 and June 2005, 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 2004 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.

ESTIMATING POPULATIONS OF PARTICULAR INDIGENOUS COUNCILS

24 Since the 2001 Census, several SLAs/LGAs have been introduced to the ASGC for which the ABS has not been able to estimate recent population change, in particular the Aboriginal Council (AC) and Island Council (IC) areas in Queensland (these ACs have since become Shires), Community Government Council (CGC) areas in Northern Territory, and Aboriginal Council (AC) areas in South Australia. Previously, the populations of these areas were included within the former SLA boundaries as defined in earlier versions of the ASGC.

25 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.

26 For the Queensland areas, additional administrative data and local knowledge was used to estimate for population change from 30 June 2001 to 2002. However, the ABS has 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.

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. For the Queensland areas a significant change occurred in a previously used data source limiting its suitability for estimating population change for these SLAs from 2002 onwards. Further, 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. 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 Where the ABS has not been able to estimate annual population change, estimates in this publication have been represented as "np". In the accompanying electronic releases, 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 2005 to ensure individual estimates sum to totals. Although these estimates indicate no change in population over this period, it should not be assumed that this is the case. The most recently prepared estimates for these areas in Queensland (30 June 2002) and the Northern Territory (30 June 2001) are contained in the 2002-03 issue of this publication. The most recently prepared estimates (30 June 2001) for the South Australian SLAs/LGAs of Anangu Pitjantjatjara (AC) and Maralinga Tjarutja (AC) were 2,672 and 137 people respectively.

29 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

30 Service population estimates are a different measure of population. They take into account seasonal itinerant populations which are not included in the ERP. Currently the ABS does not produce service population estimates but two working papers are available which investigate the concept and feasibility of such estimates. The working papers are available on the ABS web site <www.abs.gov.au> by selecting Themes, then Demography, then ABS Demography Working Papers (numbers 96/4 and 99/3).

CORRECTION OF PRISON DATA OF QUEENSLAND

31 For the 2001 Census of Population and Housing, most prison data was received for processing via electronic data files. During the post-processing evaluation cycle, it was established that the male and female counts for Queensland prisons (only) were incorrectly captured. This resulted in the publication of incorrect sex census counts for males and females for various Queensland geographical areas and as a consequence, the Australian population totals. For population estimates, revisions to Queensland were applied over the financial year 2001-02. Revised estimates for 30 June 2002 by age and sex and SLA/LGA are available. Revision to population estimates for the 1996-2001 intercensal period are not planned. However, information on the SLAs and LGAs and other geographic areas affected is available in the 2001 Census Working Paper - Fact Sheet: Correction of Prison Data of Queensland on the ABS web site <www.abs.gov.au>.

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 Australian Standard Geographical Classification (ASGC) 2005 Edition, which refers to boundaries as defined at 1 July 2005. 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 geographical 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.
• 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 Estimated resident population data for Remoteness Areas (RAs) are published here for the first time. 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 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, 2005 (cat. no. 1216.0).

MAPS

37 A complete series of SLA maps is available in Australian Standard Geographical Classification, 2005 (cat. no. 1216.0).

38 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.

39 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.

AVERAGE ANNUAL RATE OF GROWTH

40 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, P_n is the population at the end of the period and n is the length of the period between P_n and P₀ in years.

CALCULATION OF AREAS

41 The area figures quoted in this issue are based upon the SLA level of the Australian Standard Geographical Classification, 2005 (cat. no. 1216.0). The areas of the SLAs were calculated using ABS standard Geographic Information Systems software from the digital boundaries of the ASGC Edition 2005. Higher level spatial unit area figures are aggregations of the relevant SLA areas.

ELECTRONIC DATA

42 Annual population estimates at 30 June for all SLAs 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 in Australia, are freely available from the ABS web site <www.abs.gov.au>.

ACKNOWLEDGMENT

43 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

44 Other ABS releases that may be of interest to users of this publication include:

Regional Population Growth, Australia, Electronic Delivery, 2004-05, (cat. no. 3218.0.55.001)
Census of Population and Housing: Population Growth and Distribution, Australia, 2001, (cat. no. 2035.0)
Australian Demographic Statistics, (cat. no. 3101.0)
Australian Historical Population Statistics, (cat. no. 3105.0.65.001), available on <www.abs.gov.au>
Population by Age and Sex, Australian States and Territories, (cat. no. 3201.0)
Population by Age and Sex, (cat. no. 3235.0-8.55.001) - state and territory-specific datasets, available on <www.abs.gov.au>
Regional Statistics, (cat. no. 1362.1-4,1362.6-8) - state and territory-specific publications
Australian Standard Geographical Classification (ASGC), 2005, (cat. no. 1216.0)

46 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.

47 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.