Ethnic differences in mortality and hospital admission in a New Zealand population with type 2 diabetes
Authors: Mathew Hobbs, Annabel Ahuriri-Driscoll, Philip J Schluter
Journal: The Lancet Global Health (2020)

Approximately 71% of all global deaths are attributable to non-communicable diseases.1WHONoncommunicable diseases: key facts.https://www.who.int/news-room/fact-sheets/detail/noncommunicable-diseasesDate: 2018Date accessed: September 26, 2020Google Scholar Type 2 diabetes represents one of the largest and fastest-growing non-communicable diseases in Aotearoa New Zealand (New Zealand).2Health Quality & Safety Commission New ZealandDiabetes.https://www.hqsc.govt.nz/our-programmes/health-quality-evaluation/projects/atlas-of-healthcare-variation/diabetes/Date: 2020Date accessed: September 26, 2020Google Scholar In The Lancet Global Health, Dahai Yu and colleagues3Yu D Zhao Z Osuagwu UL et al.Ethnic differences in mortality and hospital admission rates between Māori, Pacific, and European New Zealanders with type 2 diabetes between 1994 and 2018: a retrospective, population-based, longitudinal cohort study.Lancet Glob Health. 2020; (published online Oct 15.)https://doi.org/10.1016/S2214-109X(20)30412-5Summary Full Text Full Text PDF Scopus (12) Google Scholar investigate ethnic differences in mortality and hospital admission rates in a New Zealand population with type 2 diabetes between 1994 and 2018, outlining long-term temporal trends in clinical outcomes between Māori, Pacific, and European ethnic groups. The study used a retrospective cohort of patients from the Diabetes Care Support Service (DCSS), the data from which were linked with national death registration, hospital admission, pharmaceutical claim, and socioeconomic status databases to estimate cause-specific mortality and hospital admission rates.3Yu D Zhao Z Osuagwu UL et al.Ethnic differences in mortality and hospital admission rates between Māori, Pacific, and European New Zealanders with type 2 diabetes between 1994 and 2018: a retrospective, population-based, longitudinal cohort study.Lancet Glob Health. 2020; (published online Oct 15.)https://doi.org/10.1016/S2214-109X(20)30412-5Summary Full Text Full Text PDF Scopus (12) Google Scholar Overall, the results indicate that poorer health outcomes have persisted among Māori and Pacific people with type 2 diabetes over time compared with European patients. There are notable strengths to this study;3Yu D Zhao Z Osuagwu UL et al.Ethnic differences in mortality and hospital admission rates between Māori, Pacific, and European New Zealanders with type 2 diabetes between 1994 and 2018: a retrospective, population-based, longitudinal cohort study.Lancet Glob Health. 2020; (published online Oct 15.)https://doi.org/10.1016/S2214-109X(20)30412-5Summary Full Text Full Text PDF Scopus (12) Google Scholar the novel period and cohort effect modelling add to the analytical robustness of the reported estimates. However, the suggestion that, “the extent of the disparities in mortality and hospital admission rates between Māori, Pacific, and European New Zealanders with type 2 diabetes in the 21st century is unknown”, is perhaps overstated. For instance, death registrations and hospital admissions attributable to type 2 diabetes are published annually and confirm ethnicity-related disparities.2Health Quality & Safety Commission New ZealandDiabetes.https://www.hqsc.govt.nz/our-programmes/health-quality-evaluation/projects/atlas-of-healthcare-variation/diabetes/Date: 2020Date accessed: September 26, 2020Google Scholar It is also well established that both Māori and Pacific peoples are significantly more likely to suffer diabetes-related morbidities, complications, and death than European New Zealanders.4Cram F Improving Māori access to diabetes health-care: literature review. Katoa, Auckland, New Zealand2014Google Scholar, 5New Zealand Guidelines GroupManagement of type 2 diabetes. New Zealand Guidelines Group, Wellington, New Zealand2011Google Scholar, 6Harwood M Tipene-Leach D Diabetes.in: Robson B Harris R Hauora: Māori Standards of Health IV. A study of the years 2000–2005. Te Rōpū Rangahau Hauora a Eru Pōmare, Wellington, New Zealand2007: 160-167Google Scholar Nevertheless, there are limitations to such national datasets that the DCSS data promises to address.3Yu D Zhao Z Osuagwu UL et al.Ethnic differences in mortality and hospital admission rates between Māori, Pacific, and European New Zealanders with type 2 diabetes between 1994 and 2018: a retrospective, population-based, longitudinal cohort study.Lancet Glob Health. 2020; (published online Oct 15.)https://doi.org/10.1016/S2214-109X(20)30412-5Summary Full Text Full Text PDF Scopus (12) Google Scholar For example, the Virtual Diabetes Register relies on health service utilisation data that is “consistent with diabetes care”, rather than formal clinical diagnosis or laboratory results. Moreover, indicators reported in the Virtual Diabetes Register combine cases of type 1 and type 2 diabetes, and owing to limitations with data availability, particular outcome indicators cannot be investigated, such as the proportion of patients who develop retinopathy.2Health Quality & Safety Commission New ZealandDiabetes.https://www.hqsc.govt.nz/our-programmes/health-quality-evaluation/projects/atlas-of-healthcare-variation/diabetes/Date: 2020Date accessed: September 26, 2020Google Scholar A key consideration when interpreting the findings presented by Yu and colleagues,3Yu D Zhao Z Osuagwu UL et al.Ethnic differences in mortality and hospital admission rates between Māori, Pacific, and European New Zealanders with type 2 diabetes between 1994 and 2018: a retrospective, population-based, longitudinal cohort study.Lancet Glob Health. 2020; (published online Oct 15.)https://doi.org/10.1016/S2214-109X(20)30412-5Summary Full Text Full Text PDF Scopus (12) Google Scholar is the use of a so-called prioritised ethnicity. Prioritised ethnicity involves classifying people with two or more ethnic identifications into a single group, with the following order of priority: Māori, Pacific, Asian, and European or other.7Reid G Bycroft C Gleisner F Comparison of ethnicity information in administrative data and the census. Statistics New Zealand, Wellington, New Zealand2016Google Scholar Therefore, a person identifying as both Pacific and Māori would be classified as Māori. Prioritised ethnicity is not recommended by Statistics New Zealand, as it hides non-Māori minority groups.7Reid G Bycroft C Gleisner F Comparison of ethnicity information in administrative data and the census. Statistics New Zealand, Wellington, New Zealand2016Google Scholar In a national study of primary school children, 33 012 (12·9%) of 255 093 identified as Pacific, but only 22 914 (9·0%) would be classified as such using a prioritised system, with the remaining children classified as Māori.8Schluter PJ Audas R Kokaua J et al.The efficacy of preschool developmental indicators as a screen for early primary school-based literacy interventions.Child Dev. 2020; 91: e59-e76Crossref PubMed Scopus (8) Google Scholar The capture of ethnic identity also depends on the data source. For instance, fewer people have multiple ethnic identifications recorded in mortality records than in census data, or in death registrations than in birth registrations. This prioritised ethnicity classification system again results in smaller counts of non-Māori minority ethnic groups compared with the groups with higher priority.7Reid G Bycroft C Gleisner F Comparison of ethnicity information in administrative data and the census. Statistics New Zealand, Wellington, New Zealand2016Google Scholar The definition and robustness of ethnicity is particularly pertinent if ethnic comparisons are made. This classification could explain the unexpected finding that most cause-specific mortality rates did not differ significantly between Pacific and European patients with type 2 diabetes.3Yu D Zhao Z Osuagwu UL et al.Ethnic differences in mortality and hospital admission rates between Māori, Pacific, and European New Zealanders with type 2 diabetes between 1994 and 2018: a retrospective, population-based, longitudinal cohort study.Lancet Glob Health. 2020; (published online Oct 15.)https://doi.org/10.1016/S2214-109X(20)30412-5Summary Full Text Full Text PDF Scopus (12) Google Scholar Indeed, according to national datasets, the prevalence of diabetes is highest among Pacific people, and the associated health outcomes are similarly poor in (if not poorer than) Māori people.2Health Quality & Safety Commission New ZealandDiabetes.https://www.hqsc.govt.nz/our-programmes/health-quality-evaluation/projects/atlas-of-healthcare-variation/diabetes/Date: 2020Date accessed: September 26, 2020Google Scholar A further consideration is that, in accordance with REporting of studies Conducted using Observational Routinely-collected Data reporting guidelines,9Benchimol EI Smeeth L Guttmann A et al.The reporting of studies conducted using observational routinely-collected health data (RECORD) statement.PLoS Med. 2015; 12e1001885Crossref PubMed Scopus (1540) Google Scholar the source data for each variable of interest should be described, including sociodemographic characteristics. The methods of linkage and linkage quality evaluation should also be provided, as there could be differential levels of engagement with and inclusion in the DCSS for different ethnic groups. The importance and effect of these non-sampling biases are difficult to ascertain. On another technical note, Yu and colleagues3Yu D Zhao Z Osuagwu UL et al.Ethnic differences in mortality and hospital admission rates between Māori, Pacific, and European New Zealanders with type 2 diabetes between 1994 and 2018: a retrospective, population-based, longitudinal cohort study.Lancet Glob Health. 2020; (published online Oct 15.)https://doi.org/10.1016/S2214-109X(20)30412-5Summary Full Text Full Text PDF Scopus (12) Google Scholar used Poisson regression, which is theoretically constrained by having a dispersion index equal to one. However, this assumption is often unrealistic. We would welcome further analyses that include relevant model diagnostics (especially given that a novel analytic approach was used) alongside a report of the implications of using prioritised ethnicity. We applaud the sophisticated empirical attention to type 2 diabetes. The use of appropriately analysed, routinely collected datasets is to be encouraged. However, the scale and erudition of such an approach can be seductive; hiding or diminishing data blind spots or nuances. The results of the study by Yu and colleagues3Yu D Zhao Z Osuagwu UL et al.Ethnic differences in mortality and hospital admission rates between Māori, Pacific, and European New Zealanders with type 2 diabetes between 1994 and 2018: a retrospective, population-based, longitudinal cohort study.Lancet Glob Health. 2020; (published online Oct 15.)https://doi.org/10.1016/S2214-109X(20)30412-5Summary Full Text Full Text PDF Scopus (12) Google Scholar are in direct contrast to extant evidence of diabetes outcomes and risk factors. In addition to the finding regarding outcomes in Pacific patients noted above, and contrary to current New Zealand guidelines for diabetes management,5New Zealand Guidelines GroupManagement of type 2 diabetes. New Zealand Guidelines Group, Wellington, New Zealand2011Google Scholar which identify smoking as a moderate-to-high risk for diabetes-related complications, and obesity as a risk factor for diabetes screening,6Harwood M Tipene-Leach D Diabetes.in: Robson B Harris R Hauora: Māori Standards of Health IV. A study of the years 2000–2005. Te Rōpū Rangahau Hauora a Eru Pōmare, Wellington, New Zealand2007: 160-167Google Scholar the authors found that the worse outcomes in Māori patients compared with European patients were independent of both risk factors. The results also question the significance of socioeconomic deprivation and reduced access to care in this particular cohort. When research differs substantially from current knowledge, the study design should bear additional scrutiny, and caution should be exercised in the interpretation of results. The findings led the authors to suggest that, “underlying biological mechanisms and the role of current or historical inequities”, warrant further research.3Yu D Zhao Z Osuagwu UL et al.Ethnic differences in mortality and hospital admission rates between Māori, Pacific, and European New Zealanders with type 2 diabetes between 1994 and 2018: a retrospective, population-based, longitudinal cohort study.Lancet Glob Health. 2020; (published online Oct 15.)https://doi.org/10.1016/S2214-109X(20)30412-5Summary Full Text Full Text PDF Scopus (12) Google Scholar While the contribution of biological mechanisms to the development of diabetes in Māori and Pacific peoples is not disputed,4Cram F Improving Māori access to diabetes health-care: literature review. Katoa, Auckland, New Zealand2014Google Scholar this factor is not a primary focus of current equity initiatives, in which patient empowerment, improved health service access, and systemic transformation are sought.10Harwood M Tane T Broome L et al.Mana Tū: a whānau ora approach to type 2 diabetes.N Z Med J. 2018; 131: 76-83PubMed Google Scholar There are good reasons for a structural rather than a biological orientation, including concern about the potential for ethnic health disparities to be misinterpreted as natural or inherent to ethnicity rather than socially produced,6Harwood M Tipene-Leach D Diabetes.in: Robson B Harris R Hauora: Māori Standards of Health IV. A study of the years 2000–2005. Te Rōpū Rangahau Hauora a Eru Pōmare, Wellington, New Zealand2007: 160-167Google Scholar and not least the desire to create the non-discriminatory conditions in which broader population health might flourish.10Harwood M Tane T Broome L et al.Mana Tū: a whānau ora approach to type 2 diabetes.N Z Med J. 2018; 131: 76-83PubMed Google Scholar We declare no competing interests. Ethnic differences in mortality and hospital admission rates between Māori, Pacific, and European New Zealanders with type 2 diabetes between 1994 and 2018: a retrospective, population-based, longitudinal cohort studyCompared with European patients, poorer health outcomes have persisted among Māori and Pacific people with type 2 diabetes for more than 20 years. New policies supporting prevention and more intensive management of type 2 diabetes are urgently needed. Research into the biological and societal mechanisms underlying these disparities, and the associated differences between Māori and Pacific patients is also needed. Full-Text PDF Open Access