Linkage findings
Scope of the data
Version 1 of the COVID-19 Register had around 250,000 records linked to a range of administrative data sets. Version 2 had an expanded data coverage to more than 6 million linked records with more recent case data (New South Wales), more jurisdictions (Victoria and Queensland) and more data sets. Version 2.5 includes case data for Tasmania, Northern Territory, Victoria and the Australian Capital Territory to 31 December 2022 and updated hospitals data for the Australian Capital Territory, Victoria, New South Wales, Queensland and Tasmania (to June 2022). Table 1 provides an overview of the data sets and coverage between the versions.
Please refer to the data variables list for the temporal scope of each of the datasets and how it differs between versions.
| Data set | Version 1 (released in December 2022) Number of linked records = 250,821 | Version 2 (released in November 2023) Number of linked records = 6,415,740 | Version 2.5 (released in February 2024) Number of linked records = 7,256,727 |
|---|---|---|---|
| State/territory notifiable disease data on COVID-19 cases | ACT NSW NT SA Tas | ACT NSW (updated data) NT SA Tas Vic (new) Qld (new) | ACT (12/03/20–31/12/22) NSW (25/01/20–30/09/22) NT (21/02/20–31/12/22) SA (30/01/20–11/02/22) Tas (30/03/20–31/12/22) Vic (25/01/20–31/12/22) Qld (28/01/20–20/08/22) |
| Medicare Consumer Directory (MCD) | Yes | Yes | Yes |
| National Death Index (NDI) | Yes | Yes | Yes |
| Medicare Benefits Schedule (MBS) | Yes Cases only | Yes Whole of population | Yes Whole of population |
| Pharmaceutical Benefits Scheme (PBS, including Repatriation Schedule of Pharmaceutical Benefits (RPBS) information) | Yes Cases only | Yes Whole of population | Yes Whole of population |
| Australian Immunisation Register | Yes Whole of population | Not available | Yes Whole of population |
| National Notifiable Disease Surveillance System (NNDSS) | Yes Cases only | Yes Cases only | Yes Cases only |
| National Hospitals Morbidity Database (NHMD) | Yes Cases only | Yes Whole of population | Yes Whole of population |
| National Non-Admitted Patient Emergency Department Care Database (NNAPEDCD) | Yes Cases only | Yes Whole of population | Yes Whole of population |
| National Aged Care Data Clearinghouse (NACDC) | Yes Cases only | Yes Whole of population | Yes Whole of population |
| National Disability Insurance Scheme (NDIS) | Not available | Not available | Yes Whole of population |
| Australian New Zealand Intensive Care Survey (ANZICS) Adult Patient Database (APD) | Not available | Not available | Yes Whole of population |
| Australian and New Zealand Paediatric Intensive Care Registry (ANZPICR) | Not available | Not available | Yes Whole of population |
Linkage rates by jurisdiction
Generally, linkage results depend on the accuracy and completeness of the linkage variables provided to the AIHW: more accurate and complete data result in better linkage rates. For more information on how the data are linked, please refer to the above section on Data and methods.
Figure 2 shows the number of records that were linked and those that were unable to be linked by state and territory. For most jurisdictions, linkage rates have generally remained the same or improved slightly, where over 90% of records supplied for the project were linked in Versions 1, 2 and 2.5. The exception is Tasmania where the proportion of linked cases fell from 99% in Version 2 to 89% in Version 2.5. This is due to the notable increase in cases from Version 2 (243) to Version 2.5 (282,277), and the high proportion of cases with missing address information, for example, 63% of cases were missing the ‘city’ variable, and 74% were missing the ‘street1’ variable.
There were notable increases in the number of records supplied from the Australian Capital Territory and Northern Territory between Version 2 and Version 2.5. The linkage rate improved slightly, from 96% to 98% for the Australian Capital Territory and from 93% to 97% for the Northern Territory. New data supplies for South Australia, Queensland and New South Wales will be reflected in the next version of the COVID-19 Register, anticipated in April 2024.
Figure 2: Number of records and percentage linked by jurisdictions across versions
This bar chart shows the linkage rates for most jurisdictions have remained the same or improved slightly across versions of the COVID-19 Register.
Note: Results for Version 1 are based on participating states and territories and will not be directly comparable to the figures in the previous web report ‘Establishing a COVID-19 linked dataset’, which includes Victoria (released 16 December 2022).
Source: COVID-19 Register
https://www.aihw.gov.au
Linkage rates by population groups
Table 2 describes the linkage rates by age group and sex/gender. Linkage rates can differ by population groups, and it is important to consider this when conducting analysis on linked data. Table 2 shows that the linkage rate largely improved for Version 2 compared to Version 1, where the linkage rate for all groups was well over 90%, except the ‘Other’ sex/gender category. This has remained similar for Version 2.5. Sex is one of the key variables used to link records, therefore, where sex is not reported consistently, or as neither male nor female (‘Other’ in Table 2 below) linkage rates are lower. The linkage rate for ‘Other’ considerably improved from 3% in Version 1 to about 77% in Version 2 and Version 2.5, though the linkage rate remains lower than males or females. There were no other large differences observed in linkage rates across the age groups.
| Version 11 | Version 2 | Version 2.5 |
|---|---|---|---|
Sex/gender2 |
|
|
|
Male | 125,673 (96.4%) | 3,020,677 (97.7%) | 3,403,063 (96.8) |
Female | 125,075 (97.2%) | 3,382,173 (97.8%) | 3,836,445 (97.0) |
Other3 | 73 (3.0%) | 13,765 (77.3%) | 18,433 (77.5) |
Age group4 |
|
|
|
0-15 | 47,241 (96.6%) | 1,141,652 (97.2%) | 1,281,183 (95.8) |
16-29 | 73,074 (95.1%) | 1,463,851 (97.2%) | 1,638,564 (96.0) |
30-49 | 79,326 (95.9%) | 2,104,378 (98.3%) | 2,373,946 (97.4) |
50-69 | 39,433 (96.9%) | 1,253,801 (98.8%) | 1,430,191 (97.9) |
70+ | 11,747 (95.9%) | 452,888 (94.7%) | 534,007 (96.8) |
Additional data on linkage rates by population groups are available in the supplementary tables.
- Results for Version 1 (released on 16 December 2022) are based on those participating states and territories as detailed in Figure 2 and will not be directly comparable to the figures in the previously released web report ‘Establishing a COVID-19 linked dataset’ which also includes Victoria.
- As reported by the state and territory.
- Other includes records where sex or gender is not reported, or sex is reported as neither male nor female.
- Age group is based on age as at 31 December 2022. Records with missing information on birth date are excluded. Person IDs with more than one year of birth and/or sex were restricted to the most recent notification date (only small number of records were affected). Where the notification dates were equal, a random record was used.