Identifying Maori ethnicity for estimating trends in fatal and serious non-fatal injury

Objectives: Counts of mortality and morbidity based on routinely collected national datasets have undercounted Maori, the indigenous people of New Zealand. To correct for the undercount, when estimating fatal and serious non-fatal injury incidence, the 'ever-Maori' method has been used. This study sought to determine how well the ever-Maori method corrects for the undercount. Methods: Trends in frequencies and age-standardised rates for fatal injury indicators were compared using: (a) ever-Maori classification; (b) New Zealand Census Mortality Study adjustment ratios applied to Total Maori counts from the Mortality Collection; and (c) Total Maori counts from the Mortality Collection. For serious non-fatal injury, trends using ever-Maori were compared with Total Maori from hospital discharge data. Results: The absolute number of injuries attributable to Maori varied depending on the method used to adjust for ethnicity status, but trends over time were comparable. Conclusions and implications: At present, there is no optimal method for adjusting for the undercount of Maori in routinely collected health databases. Reassuringly, trends in fatal and serious non-fatal injury are similar across the methods of adjusting for the undercount.