Weighting is the process of adjusting a sample to infer results for the relevant population. To do this, a 'weight' is allocated to each sample unit - in this case, persons. The weight can be considered an indication of how many people in the relevant population are represented by each person in the sample. Weights were created for linked records in the ACLD to enable longitudinal population estimates to be produced. Cross-sectional population estimates for 2006 and 2011 are available from each Census.
The ACLD began as a random sample of 5% of the Australian population in 2006. As such, each person in the sample should represent about 20 people in the population. Between Censuses, however, the in scope population changes as people die or move overseas. In addition, Census net undercount and data quality can affect the capacity to link equivalent records across waves. The ACLD weighting process, benchmarked the linked ACLD records to the population that was in scope of both the 2006 and 2011 Censuses. The weights were based on four components: the design weight, undercoverage adjustment, missed link adjustment and population benchmarking.
The original population benchmark was the 2011 Estimated Resident Population (ERP). The 2011 ERP was chosen over the 2006 ERP as the baseline population as it is more recent. The ERP was than adjusted to exclude births and overseas arrivals that had occurred between 2006 and 2011.
Weights were benchmarked to the following population groups:
- state by age (ten year groups), by sex, by mobility (interstate arrivals benchmarked separately)
- Indigenous status by state.
Note that the ERP by Indigenous status for the period 2006 - 2011 is currently being revised in view of a higher than expected intercensal increase in the number of Aboriginal and Torres Strait Islander persons (see Census of Population and Housing: Understanding the Increase in Aboriginal and Torres Strait Islander Counts, 2006-2011
(cat. no. 2077)). As a result, weights for the ACLD will be reviewed when this data becomes available.
The initial weights have a mean value of 23.3 and range between 4 and 168. Higher weights are associated with people of Aboriginal and Torres Strait Islander origin and people who moved interstate between 2006 and 2011.
For more information see the Appendix