Applying Indigenous identity definitions in official health statistics: a case study using linked cancer registry data on stomach cancer.

Abstract

Aim: Ethnicity and descent are two different officially recognised identity definitions for the Indigenous Māori population of New Zealand. Official health statistics are usually reported by Māori ethnicity but not descent, as health collections such as the New Zealand Cancer Registry (NZCR) do not record Māori descent information. We explored the potential of linked administrative data to describe health outcomes by Māori descent using gastric (stomach) cancer as an example.

Methods: The Integrated Data Infrastructure (IDI) was used to source information on Māori descent from the 2013 and 2018 censuses as well as birth and death records linked to the NZCR for gastric cancer registrations for the years 1995-2021 (N=10,575).

Results: Māori descent information could be sourced for 81.8% of gastric cancer registrations. Descent information was available for 65.2% of gastric cancer registrations in death records, 39.5% in the 2013 or 2018 census, 6.1% from a child's birth record and ≤0.3% from personal birth records. Of the registrations for whom Māori descent information could be obtained, 18.6% were identified as being of Māori descent vs 17.3% identified as Māori by ethnicity. Missing Māori descent data was lower (around 5%) in more recent gastric cancer registrations (2012 onwards).

Conclusion: Based on our case study, classifying cancer registrations by Māori descent for health outcome reporting, in addition to Māori ethnicity, may be feasible for recent years of data. Use of death records for Māori descent information should be carefully considered, as this may introduce bias to analyses such as survival analysis.