The epidemiology of breast cancer in Maori women in Aotearoa New Zealand: implications for ethnicity data analysis.
OBJECTIVE
To describe the methods used to estimate breast cancer incidence and mortality in Maori and non-Maori women using multiple adjustors to assign ethnicity.


METHODS
Age-specific incidence and mortality rates for breast cancer in Maori and non-Maori were calculated using registration and deaths data obtained from New Zealand Health Information Service (NZHIS) for 1996-2000. Four different methods were used to assign total and sole ethnicity: New Zealand Census Mortality Study (NZCMS)-adjusted, ever Maori-adjusted, National Health Index (NHI)-adjusted, and unadjusted source information.


RESULTS
Unadjusted and NHI-adjusted estimates were least similar to the NZCMS-adjusted estimate used as the 'gold standard' in this study. Ever Maori-adjusted results closely approximated NZCMS-adjusted results in both incidence and mortality data. Sole Maori breast cancer incidence and mortality estimates were generally higher than total Maori estimates.


CONCLUSIONS
Using four different estimates to assign ethnicity confirms previous findings showing poor quality of ethnicity data in routinely collected datasets. Future calculations of breast cancer incidence and mortality rates should assign total and sole ethnicity and reduce ethnicity misclassification by using NZCMS or ever Maori-adjusted estimates. This paper supports the need to collect better quality ethnicity data in order to identify and monitor Maori vs non-Maori cancer inequalities.
Curtis
Elana
E
Division of General Internal Medicine, University of California San Francisco, San Francisco, USA.
Wright
Craig
C
Wall
Madeleine
M
D001943:Breast Neoplasms / Q000208:ethnology* / Q000401:mortality*; D019352:Censuses; D003627:Data Interpretation, Statistical; D005260:Female; D006801:Humans; D015994:Incidence; D009520:New Zealand / Q000453:epidemiology; D012042:Registries; D044465:White People