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
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4. LINKAGE RESULTS

Of the 177,380 death records, 159,657 (90.0%) records were linked to one of 22,485,854 eligible Census records. Of the 3,246 Aboriginal and Torres Strait Islander death records, 2,315 (71.3%) were linked.

Examination of the characteristics of the links identified and the unlinked records can be found in 4.3 Characteristics of linked and unlinked Death registrations.

4.1 LINKAGE ACCURACY

The following quality measures were calculated for the linkage and indicate a good level of overall quality:

• The linkage rate, 90%, being the proportion of Death registrations linked to a 2016 Census record; and
• The estimated proportion of correctly linked records, otherwise referred to as 'linkage precision'.

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
 Description Records Number Census records eligible for linking(a) 22 485 854 Aboriginal and Torres Strait Islander Census records 649 171 Records on death file(b) 177 380 Death records linked 159 657 Death records not linked 17 723 Aboriginal and Torres Strait Islander records on death file(c) 3 246 Aboriginal and Torres Strait Islander records linked(c) 2 315 Percent All death records linked 90.0 Aboriginal and Torres Strait Islander death records linked 71.3
(a) Excludes residents temporarily overseas on Census night, imputed records and Census net undercount adjustment.
(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
 Total death records Linked records Linked records Reported characteristics in death registration no. no. % Sex Males 91 143 80 796 88.6 Females 86 237 78 861 91.4 Age (years) 0-14 686 435 63.4 15-24 1 219 868 71.2 25-44 5 704 3 974 69.7 45-64 22 543 18 582 82.4 65-74 27 979 25 066 89.6 75 and over 119 247 110 730 92.9 Indigenous Status Aboriginal and Torres Strait Islander 3 246 2 315 71.3 Non-Indigenous 173 186 156 546 90.4 Not stated 948 796 84.0 State of usual residence New South Wales 59 887 54 077 90.3 Victoria 43 130 38 915 90.2 Queensland 34 017 30 463 89.6 South Australia 15 349 14 045 91.5 Western Australia 16 269 14 439 88.8 Tasmania 5 315 4 832 90.9 Northern Territory 1 077 785 72.9 Australian Capital Territory 2 294 2 066 90.1 Marital status Never married 18 547 14 774 79.7 Married 70 298 64 811 92.2 Widow 64 004 59 249 92.6 Divorced 18 268 15 807 86.5 Separated 152 123 80.9 Not applicable (<15 years) 6 111 4 893 80.1 Elapsed time between Census and death Within 6 months of Census 80 234 71 238 88.8 Beyond 6 months of Census 97 146 88 419 91.0

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
 Indigenous Status State of Usual Residence Aboriginal and Torres Strait Islander Non-Indigenous Not Stated (a) New South Wales 676 52 415 474 Victoria 145 38 689 115 Queensland 663 29 997 66 South Australia 143 13 887 15 Western Australia 354 13 987 98 Tasmania 46 4 787 - Northern Territory 272 501 - Australian Capital Territory 16 2 283 24 Total 2 315 156 546 796
(a) Small cell counts have been suppressed to preserve confidentiality.

4.4 REASONS FOR UNLINKED DEATH REGISTRATIONS

There were two main reasons why death registrations were not linked to a Census record:
1. Records belonging to the same individual were present in the Death registration and Census datasets but these records failed to be linked because they contained missing or inconsistent information; or
2. A link was not possible because there was no Census record corresponding to the death registration as the person was missed from the Census. Proximity of death to Census night is a significant factor in the ability for a link to be achieved.

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:
• the missing or inconsistent information did not allow the record pair to be compared in the same blocking categories and could not be linked;
• the record pair did not contain enough unique common information to distinguish the match from other potential record pairs;
• the record pair was linked, but was attributed a low link weight as it contained substantial missing or inconsistent information and was positioned below the cut-off identified in sample clerical review; or
• the record pair was subjected to clerical review, but the high level of inconsistency prevented it from being deemed a true link.

Inconsistent Census information may be recorded due to a range of factors, including:
• transcription errors in the Census, where the wrong category is selected or the information is transposed, such as the day the person was born being reported in the month field instead of in the day field;
• data capture errors, where the Census form is scanned using Optical Character Recognition (OCR) software and certain characters may be misclassified, such as a 1 captured as a 7 or a 3 as an 8;
• reporting errors, where information is given for the wrong member of the household (e.g. person 1's information is reported for person 3) or where the person completing the Census form for a household guesses or estimates information about a fellow household member; or
• information that was not stated by the respondent and has been imputed as part of Census processing (such as age or sex), while set to missing for linking, the imputed values are included in the analytical dataset.

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
 Year of Death Month of Death Total Death Registrations no. Linked Death Registrations no. Linked Death Registrations % 2016 August 4 220 3 250 77.0 September 14 054 12 160 86.5 October 12 775 11 508 90.1 November 13 753 12 437 90.4 December 11 398 10 285 90.2 2017 January 12 703 11 522 90.7 February 11 843 10 718 90.5 March 13 454 12 240 91.0 April 10 331 9 370 90.7 May 14 766 13 407 90.8 June 13 906 12 636 90.9 July 13 043 11 879 91.1 August 16 053 14 579 90.8 September 15 081 13 666 90.6

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