Australian Bureau of Statistics
3228.0.55.001 - Population Estimates: Concepts, Sources and Methods, 2009
Latest ISSUE Released at 11:30 AM (CANBERRA TIME) 12/06/2009
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2.10 The Census counts of residents are then adjusted upwards to compensate for Census net undercount. In 2006, about 3.0% of the population were not counted by the Census, while 0.3% were counted more than once. These two figures produced a net undercount rate of 2.7%. The precise degree of adjustment is based on estimates of undercount from the Census Post Enumeration Survey (PES) and to a lesser degree comparisons between Census results and independent 'demographic' and other estimates of the population - see Appendix 1 - Demographic adjustment.
2.11 The PES is a sample survey conducted shortly after the Census to estimate the number of people (and their characteristics) who did not complete or were not included on a Census form. It also detects instances of multiple counting of individuals but the number of such cases is far outweighed by the number of people who are not counted. The net undercount is therefore the excess of the undercount (people not counted) over the number of instances of multiple counting.
2.12 Net undercount for each category (i.e. state, SLA, sex, age, Indigenous status) is the net result of the PES estimate of gross undercount, gross overcount, differences in classification between the PES and Census (eg. age, sex, Indigenous status) and imputation error in the Census. Details of the 2006 PES are available in:
2.13 The 'demographic' estimates are an annual population series for Australia as a whole, compiled solely from registered births and deaths and overseas migration data from 1925 onwards (i.e. they are compiled irrespective of Census counts, see Appendix 1 - Demographic adjustment).
2.14 A detailed description of the 2006 adjustment for net undercount is contained in Chapter 9 - Data sources.
2.15 Estimates of the number of Australian residents temporarily overseas on Census Night (RTOs) are obtained from passenger card statistics for those Australian residents returning in the twelve month period subsequent to the Census date who were overseas on Census Night. The residency status is calculated using the improved net overseas migration (NOM) method (see Chapter 6 - Estimating net overseas migration), and the residents are added to the adjusted Census counts derived in Step 2 to give Census year population estimates. The population estimates are then converted from age to financial year of birth, which for the 8 August 2006 Census date required adjusting all cohorts for the 39 day period back to 30 June by taking 39/365 of each cohort and adding it to the next one.
2.16 As the Census does not fall on 30 June, a further adjustment is necessary to arrive at estimates for that date. For example, the 2006 Census was held on 8 August, and after Steps 1 to 3, the population estimates at 8 August were back-dated to 30 June. This used data from birth and death registrations, overseas arrivals and departures data and estimates of interstate migration for the period 1 July to 8 August.
This page last updated 11 June 2009
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