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APPENDIX A: CALCULATING ADJUSTED LINKAGE RATES
For more information, see Census of Population and Housing: Details of Undercount, August 2011 (cat no. 2940.0.) and Australian Demographic Statistics, September 2012 (cat. no. 3101.0).
For this project, two minor modifications were made to the ERP prior to calculating the linkage adjustment factor. Both of these slightly decrease the magnitude of the linkage adjustment factor from what it would otherwise have been based on the actual ERP.
First, for total deaths, the RTO adjustment was removed from the ERP. That is, it was assumed that, on balance, people temporarily overseas at the time of the Census were unlikely to be represented in the death registration data. While there may well have been a small number of instances in which this actually occurred, it was assumed that the full RTO component would overstate the level of adjustment required.
An additional modification was made to the ERP when the ratio was applied to deaths by Indigenous status. The number of imputed Census records for which Indigenous status was not stated (item non-response only) was removed from the ERP. A not stated category for Indigenous status is included in both death registration and Census data but not the ERP. Therefore, the ratio of Census to ERP by Indigenous status may overstate the amount of undercount in death registrations if the imputation for item non-response were not removed.
The expected number of links from the death registration data was calculated as follows:
Expected links = Death registrations × Census count ÷ Modified ERP
The adjusted linkage rate is then calculated as the number of links as a proportion of expected links:
Adjusted linkage rate = Linked Death registrations ÷ Expected links
Note that this method assumes that the Census undercount rates (by Indigenous status, age group, sex and state of residence) for the general population are the same as for the population who died in the period 10 August 2011 to 27 September 2012.
As expected, the adjustments to death registration data were broadly aligned with estimates of Census undercount. Based on the results of the Post Enumeration Survey, the 2011 Census net undercount was estimated at 17.2% for the Aboriginal and Torres Strait Islander population and 6.2% for non-Indigenous persons. Comparable figures for the increase of actual death registrations over expected links were 10.5% for Aboriginal and Torres Strait Islander deaths and 3.3% for non-Indigenous deaths. Differences between the two sets of figures relate both to the minor modification to the ERP used for the adjustment factors, and the different population structure for death registrations compared with the total population.
Table A.1 - ADJUSTMENT OF DEATH REGISTRATIONS, By Indigenous status
(b) Population as estimated by the Post Enumeration Survey (PES) as of Census night (9th of August 2011).
(c) Includes imputed persons in non-responding dwellings.
While the calculation of adjusted linkage rates performed here is similar to the method used in 2006, other assumptions could be made about the likelihood of death registrations lacking a corresponding Census record. The ABS is undertaking further research to examine the effects of differential reporting of Indigenous status on raw and adjusted linkage rates.
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