Census year population estimates
3.4 The method used to compile Census date SLA population estimates is similar to that used for national and state/territory estimates.
3.5 Census counts of usual residents by SLA are adjusted for net undercount using data from the Census Post Enumeration Survey (PES) and demographic analysis. The small sample size of this survey relative to the large number of SLAs (approximately 1,400 in 2006) restricts the reliability of the PES as a direct measure of net undercount for SLAs. Consequently, net undercount for SLAs is estimated using an iterative proportional fitting method (see Appendix 5 - The iterative proportional fitting procedure) using the higher level PES data as the marginals. Based on the premise that net undercount is related to age, sex, location and Indigenous status, it is assumed that differentials for these characteristics at the SLA level reflect differentials for Census counts by age, sex, Indigenous status, state or territory, and (aside from the ACT) capital city/balance of state or territory. The Census counts by SLA, age, sex and Indigenous status are forced to add to higher-level marginal totals adjusted for undercount, using the iterative proportional fitting technique.
3.6 Estimates of the number of Australian residents temporarily overseas on Census Night (RTOs), derived from coded addresses of residence to SLA from a sample of incoming passenger cards are added to their respective SLAs. (All persons arriving in Australia, including Australian residents returning, are required to report their intended address which is taken to be the usual residence.)
3.7 As the Census is held on a date other than 30 June (the 2006 Census was held on 8 August), further adjustments taking into account births, deaths and migration for the intervening period are made to obtain the ERP at 30 June. For births and deaths, the actual events registered as occurring between these dates are taken into account. Net migration is estimated based on the relevant proportion of the population who moved within the previous 12 months as recorded in the 2006 Census. Inter-SLA migration is constrained to sum to net interstate migration levels while overseas arrivals is similarly constrained, using overseas migration data. As the Census does not collect data on overseas departures, SLAs are assumed to have the same proportion of state/territory overseas departures as they had of arrivals.
3.8 For some areas, demographic adjustments are made to these estimates. Finally, the SLA population estimates are constrained to sum to 30 June estimates for their respective states or territories.