Unlocking the numerator-denominator bias. I: Adjustments ratios by ethnicity for 1991-94 mortality data. The New Zealand Census-Mortality Study.
OBJECTIVE
To determine the extent of the under-reporting of Mäori and Pacific mortality among 0-74 year olds for the period 1991-94.


METHODS
A subset (n=22,578) of highly probable linked 1991 census and 1991-94 mortality records were selected from the 31,635 census-mortality links in the New Zealand Census-Mortality Study. The numbers of decedents assigned as Mäori, Pacific, and non-Mäori non-Pacific were compared between mortality and census data.


RESULTS
Compared to the death registration form, 29% more 0-74 year old decedents during 1991-94 had self-identified as sole-Mäori on the 1991 census (46% for prioritised-Mäori). This numerator-denominator bias was greater among the young and those living in central and southern New Zealand. Among 0-14, 15-24, 25-44, 45-64, and 65-74 year old decedents, respectively, 91%, 50%, 41%, 26% and 15% more decedents had self-identified as sole-Mäori on the 1991 census. For Northern, Midland, Central and Southern regional health authority areas, respectively, 14%, 17%, 81% and 102% more decedents had self-identified as sole-Mäori. Among Pacific decedents 68% more 0-74 year old decedents had self-identified as sole-Pacific on the 1991 census (78% for prioritised-Pacific group). This bias for Pacific decedents did not notably vary by age and region.


CONCLUSIONS
This study confirms substantial underestimation of Mäori and Pacific mortality rates for the period 1991-94, even using the recommended sole-ethnic group denominator. The results from this study should be used to adjust ethnic-specific mortality rates for the early 1990s. Population-based funding formulas that included region-specific Mäori mortality rates would have particularly disadvantaged central and southern regions.
Blakely
Tony
T
Department of Public Health, Wellington School of Medicine and Health Sciences, University of Otago, Wellington. tblakely@wnmeds.ac.nz
Robson
Bridget
B
Atkinson
June
J
Sporle
Andrew
A
Kiro
Cindy
C
D000293:Adolescent; D000328:Adult; D000368:Aged; D015982:Bias; D019352:Censuses; D002648:Child; D002675:Child, Preschool; D005007:Ethnology / Q000706:statistics & numerical data*; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D008432:Mathematical Computing; D008875:Middle Aged; D009026:Mortality; D009520:New Zealand / Q000453:epidemiology; D010139:Pacific Islands / Q000208:ethnology