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Patterns of Disparity: Ethnic and Socio-economic Trends in Breast Cancer Mortality in New Zealand

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Abstract

Objective

To test whether trends in breast cancer mortality varied by ethnicity and socio-economic position during the 1980s and ‘90s in New Zealand.

Methods

Four cohorts of the entire New Zealand population for 1981–84; 86–89; 91–94 and 96–99 allowed direct determination of socio-economic trends in breast cancer mortality. For ethnicity, unlinked routine census and mortality data were used with adjustment factors for undercounting of Māori and Pacific deaths.

Results

Māori and non-Māori non-Pacific mortality rates changed little until mid-1990s with Māori experiencing 25% higher mortality. In 1996–99, Māori rates increased notably to become 68% higher than non-Māori non-Pacific (SRR 1.68; 95% CI: 1.49–1.90). Pacific women experienced an approximate three-fold increase in breast cancer mortality over time.

There appeared to be reducing mortality among higher income and education groups but trends within socio-economic groups were not statistically significant. Nevertheless, by 1996–99, there was a significant 22% excess mortality (SRR 1.22; 95% CI: 1.01–1.49) for low compared with high-income groups.

Conclusions

Widening ethnic, and probably, socio-economic disparities in breast cancer mortality are likely due to both underlying incidence and differential survival trends. Disparities are likely to increase once the full differential mortality benefits of screening impact on the population.

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Acknowledgements

The NZCMS is conducted in collaboration with Statistics New Zealand and within the confines of the Statistics Act 1975. The NZCMS was funded by the Health Research Council of New Zealand, and is now funded by the Ministry of Health.

Summary statistics New Zealand security statement

The New Zealand Census-Mortality Study (NZCMS) is a study of the relationship between socio-economic factors and mortality in New Zealand, based on the integration of anonymised population census data from Statistics New Zealand and mortality data from the New Zealand Health Information Service. The project was approved by Statistics New Zealand as a Data Laboratory project under the Microdata Access Protocols in 1997. The datasets created by the integration process are covered by the Statistics Act and can be used for statistical purposes only. Only approved researchers who have signed Statistics New Zealand’s declaration of secrecy can access the integrated data in the Data Laboratory (A full security statement is in a technical report at http://www.wnmeds.ac.nz/nzcms-info.html). For further information about confidentiality matters in regard to this study please contact Statistics New Zealand.

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Correspondence to Diana Sarfati.

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Sarfati, D., Blakely, T., Shaw, C. et al. Patterns of Disparity: Ethnic and Socio-economic Trends in Breast Cancer Mortality in New Zealand. Cancer Causes Control 17, 671–678 (2006). https://doi.org/10.1007/s10552-005-0583-0

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  • DOI: https://doi.org/10.1007/s10552-005-0583-0

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