Cancer data in Australia

In the 2022 release of Cancer data in Australia (CdiA), two sets of mortality data were published. One set was sourced from the National Mortality Database (NMD) while the other was derived from the Australian Cancer Database (ACD). Prior to 2022, only the NMD was used to report cancer mortality.

Cancer data commentary 8 was released to help understand why two sources of data were used and Cancer data commentary 8b provides guidance on which data source to use for each type of cancer and analysis.

The release of the two data sources highlights uncertainties in mortality reporting for some cancers. The cancer mortality project is being undertaken within existing resources and aims to help progress mortality reporting and reduce uncertainties.

At present, the cancer mortality project is examining unit record differences between the ACD and NMD for liver cancer. As a cancer with more substantial differences between the NMD and ACD mortality counts, liver cancer has been selected as the cancer to trial investigations on. The differences between the cause of death according to the two sources have been considered at unit record level by comparing the cause of death data from the two data sources for each individual record. While the specific results of these investigations are not yet ready for release, the general findings to date indicate that:

• where there is inconsistency between the two data sources cause of death, the differences may be mainly driven by a small number of common inconsistencies.
• differences can impact one sex more than the other to the extent that the consistency of the cause of death information according to the NMD and ACD can be considerably greater for one sex.
• unit record investigations for liver cancer and other cancer types could provide information of benefit to both data sources.

The investigations to date suggest that examining differences in the cause of death at a unit record level will lead to improved understandings of the nature of issues. Issues are likely to be specific to each type of cancer and therefore each cancer where the ACD and NMD differ substantially will need to be investigated individually.

At a minimum, investigations should inform decisions about which data source to use for specific purposes and improve understandings of where and why differences occur. The potential beyond that is difficult to determine at this stage of the project.

It is envisaged that the cancer mortality project will continue to progress in the latter half of 2023 and the results of investigations are likely to be published in 2024.