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4. LINKAGE RESULTS
4.2 LINKAGE PRECISION
Not all record pairs assigned as links in a data linkage process are a true match, that is, a record pair belonging to the same individual. While the methodology is designed to ensure that the vast majority of links are true, some are actually false, i.e. the records in the link belong to different people rather than the same person. The linkage strategy used for the project was designed to ensure a high level of accuracy. Accordingly, the strategy was restrictive and conservative.
One of the key measures of linkage quality is the proportion of links in the dataset that are false. The number of false links is able to be estimated through the use of methods such as clerically reviewing a sample of links, or by using modelling techniques. Once an estimate of the number of false links is obtained, a 'precision' can be calculated. The precision is an estimate of the proportion of links that are matches (i.e. belonging to the same entity).
Precision = (Total links - False link estimate)/Total links
Once the precision of the dataset is estimated, the false link rate is easily calculated.
False link rate = 1 - Precision
The estimated link precision of the 2016 Death Registrations to Census linkage dataset is 100% as the decision model did not allow for any false links. As previously discussed, the upper cut-off was set such that it was estimated there were no false links above the cut-off while the clerical review process only accepted links for which there was sufficient evidence to support them being accurate matches. In reality, there will be a small number of false links due to a slight degree of inconsistent decisions between clerical reviewers. While the number of false links is not able to be quantified precisely, the proportion is expected to be very small.
4.3 CHARACTERISTICS OF LINKED AND UNLINKED DEATH REGISTRATIONS
TABLE 3 - CENSUS AND DEATH REGISTRATIONS, Australia
(b) Deaths which occurred between 09 Aug 2016 and 28 Sep 2017.
(c) According to Indigenous status reported on death registration form.
The number and percentage of death records linked to Census records by selected characteristics of deceased persons are presented in Table 4. A slightly higher linkage was achieved for females (91.4%) compared with males (88.6%). The linkage rate varied considerably by age, being lowest for 0-14 year old deceased persons (63.4%). This may be due to the comparatively high Census undercount rate in this age group. The linkage rate was highest for 75 years and older deceased persons (92.9%).
TABLE 4 - DEATH REGISTRATIONS LINKED TO CENSUS RECORDS BY SELECTED CHARACTERISTICS, Australia
The linkage success varied by state of usual residence as reported on the death registration form. Rates were highest for South Australia (91.5%) and lowest for the Northern Territory (72.9%). All other states and territories had linkage rates between 88.8% and 90.9%. The low linkage rate for the Northern Territory reflects comparatively low linkage rates for both the Aboriginal and Torres Strait Islander and non-Indigenous populations. The linkage rate was similar for married and widowed persons (92.2 and 92.6% respectively). The linkage rate was lower for deaths which occurred within six months of the Census (88.8%) than those which occurred beyond six months after the Census (91.0%).
The linkage success also varied by Indigenous status recorded on the death registration form. People of non-Indigenous origin on the death registration form had a considerably higher linkage success (90.4%) compared with people of Aboriginal and Torres Strait Islander origin (71.3%). A more strict approach to implementing the 2016 linkage clerical review resulted in a lower, but more accurate linkage rate than in 2010-2012.
TABLE 5 - DEATH REGISTRATIONS LINKED TO CENSUS RECORDS BY STATE OF USUAL RESIDENCE AND INDIGENOUS STATUS, Australia
4.4 REASONS FOR UNLINKED DEATH REGISTRATIONS
There were two main reasons why death registrations were not linked to a Census record:
MISSING AND/OR INCONSISTENT INFORMATION
The quality of a data linkage project is significantly dependent on the quality of three key sources of information, these being name, address and date of birth. When all three sources of information are of very high quality on the linking datasets, identifying true links becomes less complicated, resulting in a high quality outcome for the linkage.
In some cases, the true match was present in the pool of all record pairs but it was not identified because there was a high level of inconsistency between information on the Death registration and the 2016 Census record, or key linking fields were missing from one or both datasets. The reasons for the match being missed can be categorised into the following groups:
Inconsistent Census information may be recorded due to a range of factors, including:
Accurate address coding was crucial in narrowing the search and differentiating between true and false links. However the nature of the data did not always allow for linkage on address or geography to be possible, as people may have changed address after Census night and prior to their death (e.g. moving to a nursing home); therefore the address recorded on the death record may not have been captured on the Census
NO CENSUS RECORD
A person may have had no 2016 Census record because they were not in scope of the Census due to absence from Australia, or died in the period around Census night, or they may have been missed in the 2016 Census.
Due to the size and complexity of the Census, it is inevitable that some people are missed and some are counted more than once. It is for this reason that the Census Post Enumeration Survey (PES) is run shortly after each Census, to provide an independent measure of Census coverage. The PES determines how many people should have been counted in the Census, how many were missed (undercount), and how many were counted more than once (overcount). It also provides information on the characteristics of those in the population who have been under- or overcounted.
The net undercount rate for the 2016 Census was 1%, with a higher rate for Aboriginal and Torres Strait Islander people (17.5%) than for the non-Indigenous population (6.6%). For more information please refer to Census of Population and Housing - Details of Overcount and Undercount, Australia 2016 (cat. no. 2940.0).
In a small number of cases, the absence of a Census form could be the result of the person being overseas at the time of the Census but subsequently dying in Australia and the death registered during the linkage reference period.
TIMING OF DEATH REGISTRATION
Due to an individual generally having reduced capacity to complete a Census form when near death, deaths occurring closest to Census night are more difficult to link. That is, it is more likely that deaths in the Census enumeration month do not possess a corresponding Census record, as the Census was not completed for the individual with sufficient information for linking (note that Census counts people in institutions such as hospitals, but may not collect all information required for linking). In 2011, 10% of deaths in August were unlinked, compared to a range of 6-8% for other months. Due perhaps to an extended enumeration period in 2016, the rate of unlinked records in the month closest to Census night doubled to nearly 20%.
Rolling enumeration procedures for the 2016 Census in remote Aboriginal and Torres Strait Islander communities may have increased the likelihood of an equivalent Census record not existing for deaths of members of these communities occurring around the time of the Census. Rolling enumeration involves conducting the Census over an extended period of four weeks. In these instances it is possible that a resident who moved during the enumeration period may have been missed and therefore a corresponding Census record would not exist, or they may have passed away after Census Night (9 August 2016) but before Census enumeration was conducted in their residential area.
TABLE 6 - DEATH REGISTRATIONS LINKED TO CENSUS RECORDS BY MONTH AND YEAR OF DEATH, Australia
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3302.0.55.004 - Linking Death registrations to the 2016 Census, 2016-17
Latest ISSUE Released at 11:30 AM (CANBERRA TIME) 10/12/2018