1 This publication contains revised estimates of the resident populations (ERP) by age and sex, of Australian states and territories, as at 30 June 2006 and preliminary estimates as at 30 June 2007. Mean ages and sex ratios for the states, territories and Australia are also included. These data are based on the 2006 Census of Population and Housing.
2 Following the 1992 amendments to the Acts Interpretation Act to include the Indian Ocean Territories of Christmas Island and the Cocos (Keeling) Islands as part of geographic Australia, population estimates commencing from September quarter 1993 include estimates for these two territories. To reflect this change, another category of the state and territory level has been created, known as Other Territories. Other Territories include Jervis Bay Territory, previously included with the Australian Capital Territory, as well as Christmas Island and the Cocos (Keeling) Islands, previously excluded from population estimates for Australia. Data for Other Territories, while not detailed separately, are included in tables where specifically noted.
RESIDENT POPULATION ESTIMATES SERIES
3 Australia’s population estimates for the period since 1971 are compiled according to the place of usual residence of the population. An explanation of the place of usual residence conceptual basis for population estimates is given in Demographic Estimates and Projections: Concepts, Sources and Methods, Statistical Concepts (cat. no. 3228.0).
METHOD OF ESTIMATION
4 The estimates by age of the population of Australia and the states and territories at the date of the census are derived from the census counts by place of usual residence, by adjusting for under-enumeration and adding the number of Australian residents estimated to have been temporarily overseas at the time of the census.
5 Post-censal population estimates are obtained by advancing the previous year's estimates to the next year by subtracting deaths and adding births and net estimated interstate and overseas migration. After each census, estimates for the preceding intercensal period are revised by incorporating an additional adjustment (intercensal discrepancy) to ensure that the total intercensal increase at each age agrees with the difference between the estimated resident populations at the two respective census dates.
Natural increase: births and deaths
6 Natural increase is a major component of ABS quarterly state and territory population estimates and is calculated using the estimated number of births and deaths, by state and territory of usual residence, using year/quarter of registration for preliminary data and year/quarter of occurrence for both revised and final data. This may affect time series comparisons within relevant tables. For preliminary estimates, births and deaths by quarter of registration are used as a proxy for quarter of occurrence. For revised estimates, a factor has been applied to the number of occurrences to allow for those occurrences which were yet to be registered at the time of revision. For final estimates between 30 June 1991 and 30 June 2001, year/quarter of occurrence data are used. For further details see Demography Working Paper 1998/2 - Quarterly Birth and Death Estimates (cat. no. 3114.0).
7 The timeliness and accuracy of ABS quarterly population estimates depends in part on the timeliness and accuracy of estimates of births and deaths which are based on registrations. To be able to provide timely estimates the ABS produces preliminary estimates using births and deaths by quarter of registration as a proxy for quarter of occurrence. The major difficulty in this area stems from the fact that while the vast majority of births and deaths are registered promptly, a small proportion of registrations are delayed for months or even years. Lags or accumulations in births and deaths registrations can be caused by either:
- late notification of a birth or death event to a state or territory registry;
- delays arising from incomplete information supplied for a registration;
- procedural changes affecting the processing cycles in any of the state and territory registries; and
- resolution of issues that may arise within the ABS or registry processing systems.
Preliminary births and deaths estimates are subject to fluctuations caused by lags or accumulations in the reporting of births and deaths registrations. Accumulations can result from the eventual processing of lagged registrations in a later quarter. As a result, preliminary quarterly estimates can be an underestimate or an overestimate of the true numbers of births and deaths occurring in a reference period. Note that estimates from September quarter 2006 onwards are preliminary.
Net overseas migration
9 Conceptually, net overseas migration (NOM) is the difference between permanent and long-term arrivals, and permanent and long-term departures. Estimates of NOM are derived from information provided on incoming and outgoing passenger cards, as well as other data supplied by the Department of Immigration and Citizenship (DIAC), formerly the Department of Immigration and Multicultural Affairs (DIMA) and the Department of Immigration and Multicultural and Inidigenous Affairs (DIMIA). Data on the intended duration of stay of overseas visitors arriving in Australia and the intended duration of absence of Australian residents travelling overseas are used to initially determine the numbers of permanent and long-term arrivals, and permanent and long-term departures. Passenger card data are then used to calculate migration adjustments and determine the state and territory distribution of NOM.
10 The Australian Bureau of Statistics (ABS) has developed an improved method for calculating NOM for September quarter 2006 onwards. Estimates from the past time series based on the previous method, and the current time series based on the improved method are not comparable. Preliminary estimates for September quarter 2006 onwards based on the new method are included in Table 2 of this issue. The key change is the introduction of a '12/16 month rule' for determining a person's residency in Australia, replacing the previous '12/12 month rule'. For further information on the new improved method see Information Paper: Improved Methods for Estimating Net Overseas Migration (cat. no. 3107.0.55.003) and Information Paper: Statistical Implications of Improved Methods for Estimating Net Overseas Migration, Australia 2007 (cat. no. 3107.0.55.005).
11 The previous method used to estimate net overseas migration from September quarter 2001 to June quarter 2006 compared data on actual travel movements over a one year period with those advised by individual travellers, and are explained in more detail in Demography Working Paper 2003/5 - Net Overseas Migration: Adjusting for Actual Duration of Stay or Absence (cat. no.3137.0). In order to conduct such a comparison, data for a 15 month period (i.e. one year plus one quarter) were required.
Net interstate migration
12 Interstate migration is a key determinant of the accuracy of state and territory population estimates. Data on interstate migration can not be directly estimated. Instead, post-censal estimates of interstate migration are modelled using administrative by-product data. Currently the data used by the ABS is information on interstate changes of address advised to Medicare Australia and to the Department of Defence in the case of the military. The Medicare-based model used for generating post-censal estimates of interstate migration is largely superseded when new Census information becomes available.
13 When Census data on interstate movement becomes available part of the process of rebasing ERPs for states and territories is the re-derivation of interstate migration for the intercensal period. The overall approach is to minimise state intercensal error using data analysed from the Census questions concerning an individual's place of residence one-year ago, five-years ago and at Census night. When new Census data are available, interstate migration estimates for the intercensal period are replaced with estimates derived from Census data on place of usual residence five years ago. These estimates are then scaled so that they sum to zero at the Australian level. A similar process is carried out for the year prior to the Census, using Census data on place of usual residence one year ago. The difference between the original interstate migration estimates and the rebased estimates is apportioned across all quarters, movement categories, ages and sex categories in the intercensal period in order to minimise quarterly change.
14 Due to the non-compulsory and non-universal nature of the available (indirect) data sources, post-censal quarterly estimates of interstate migration have long been considered the weakest measure of a component of population change. For further information on the process of estimating interstate migration and the administrative data used, see the Demography Working Paper: 2004/1 Review of Interstate Migration Method (cat. no. 3106.0.55.001) and the Information Paper: Evaluation of Administrative Data Sources for Use in Quarterly Estimation of Interstate Migration, 2006 to 2011 (cat. no. 3127.0.55.001).
AVERAGE ANNUAL RATE OF GROWTH
15 The average annual growth rate, r, is calculated as a percentage using the formula: 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.
16 It should be noted that while the Australian Bureau of Statistics (ABS) seeks to produce the most accurate estimates of the population possible, the accuracy of the estimates depends on the quality of the source data used. The major source of potential error is considered to be the estimates of interstate migration based on Medicare transfer data.
17 Single year age estimates are not shown for persons aged 85 years or older. The reliability of age estimates decreases as older ages are reached. However, estimates for each age up to 99 and 100 years or more have been calculated and are available on request.
18 In recognition of the inherent accuracy involved in population estimation, population figures over 1,000 in the text are rounded to the nearest hundred, and figures less than 1,000 are rounded to the nearest ten. While unrounded figures are provided in tables, accuracy to the last digit is not claimed and should not be assumed.
19 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 in 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.
20 Previous issues of this series containing consolidated data were issued on 23 August 1982 (containing estimates for the years 1977 to 1982); 8 December 1987 (containing estimates for the years 1981 to 1987); 21 July 1993 (containing estimates for the years 1992 to 1997); 27 March 2003 (containing estimates for the years 1997 to 2002).
ADDITIONAL STATISTICS AVAILABLE
22 As well as the statistics included in this and related publications, the ABS may have other relevant data available on request. Inquiries should be made to the National Information and Referral Service on 1300 135 070.