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FEATURE ARTICLE: PRELIMINARY REBASING OF AUSTRALIA'S POPULATION ESTIMATES USING THE 2011 CENSUS OF POPULATION AND HOUSING
The second step addresses those who were missed in the census by:
The third step addresses backdating the resulting ERP figure for Census night 9 August 2011 to 30 June 2011 using the components of population change by:
These steps are illustrated in the following flow chart:
The table below shows how the ABS arrived at the Census night 9 August 2011 ERP figure for Australia, states and territories using figures obtained from applying the adjustments listed above.
INTERCENSAL ERROR AND INTERCENSAL DISCREPANCY
The intercensal error refers to the difference between the latest Census based ERP figures for 30 June 2011 and the ERP figures based on the previous Census which have been carried forward using births, deaths and migration data.
There are two areas that contribute to the intercensal error:
The table below shows the preliminary intercensal error by number and percentage of total population for the 2006-2011 period for Australia, states and territories.
Information collected in the 2011 Census will also allow the ABS to estimate approximately how much of the intercensal error is due to inaccuracies in estimates of interstate migration. In order to do this, the ABS will analyse data from the Census questions concerning an individual's place of usual residence one year ago and five years ago. These results will be released in the December 2012 issue of this publication (released in June 2013).
After the intercensal error is adjusted for revisions to the components of population change (births, deaths and migration), the remaining (unattributable) portion is referred to as the intercensal discrepancy. The estimate of intercensal discrepancy for each state and territory, birth cohort and sex are spread evenly across the intercensal quarters. Thus the intercensal discrepancy acts as a balancing item, that when combined with births, deaths and migration equals the difference between the two Census population estimates. Intercensal discrepancy is caused by errors in the start and/or finish population estimates and/or in estimates of births, deaths or migration in the intervening period which cannot be attributed to a particular source. The 2006-2011 intercensal discrepancy will be published in the December 2012 issue of this publication, to be released in June 2013.
REVISING THE 20 MOST RECENT QUARTERLY ESTIMATES TO 'PRELIMINARY REBASED'
The main purpose of revising the 20 most recent intercensal estimates (i.e. September 2006-June 2011) of quarterly population growth to 'preliminary rebased' was to ensure that the estimates from the 2006-2011 intercensal period will be comparable to all future estimates, thus creating a consistent time series of ERP data. These estimates will remain as 'preliminary rebased' until the December 2012 issue of this publication (released in June 2013) when their status will be changed for the last time to 'final rebased'. Following this, no subsequent revisions will be made to these estimates.
ADJUSTING FOR NET UNDERCOUNT
Net undercount for Australia in the 2011 Census was 374,600 persons (including additional minor coherence and quality adjustments). Net undercount is the difference between the actual Census count and the estimate of the number of people who should have been counted in the Census. This estimate is based on the PES conducted in August and September of 2011. For a category of person (based on age, sex and state of usual residence), net undercount is the resultant of Census undercount, overcount, misclassification and imputation error. Adding the net undercount of people back into the population is a crucial step in arriving at the most accurate ERP possible. For more information on measuring net undercount using the PES see Information Paper: Measuring Net Undercount in the 2011 Population Census, 2011 (cat. no. 2940.0.55.001) and Census of Population and Housing - Details of Undercount, 2011 (ABS cat. no. 2940.0).
The 2011 PES involved a considerable degree of innovation, with the most important change being the introduction of Automated Data Linking (ADL). This new methodology, which was tested in the 2006 PES employed probabilistic linking techniques, using a range of personal and address characteristics, to evaluate the likelihood that a PES and Census record pertained to the same individual. ADL therefore provided the opportunity to match persons who would have been too difficult to match previously, given the constraints of previous technology and processes.
Other notable improvements include:
For more information see Census of Population and Housing - Details of Undercount, 2011 (ABS cat. no. 2940.0).
PLANS FOR FURTHER OUTPUT
Following this issue which contains preliminary population estimates for Australia, states and territories based on the 2011 Census, the ABS will also publish final population estimates based on the 2011 Census for Australia, states and territories, for September quarter 2006 to June quarter 2011, in the December quarter 2012 issue of Australian Demographic Statistics (cat. no. 3101.0) to be released on 20 June 2013. That issue will include final rebased estimates dating back to 30 September 2006. No subsequent revisions will be made to those final rebased estimates.
Preliminary rebased estimates for SA2s and LGAs will be published in Regional Population Growth, Australia, 2011 (cat. no. 3218.0) with final rebased estimates published by mid August 2013. Preliminary rebased estimates of the Australian Aboriginal and Torres Strait Islander population at 30 June 2011 will be published by five year age groups, sex and state/territory in the next issue of this publication on 27 September 2012. No further disaggregation will be released until final estimates are compiled and released by mid August 2013.
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