Do New Zealand's immigrants have a mortality advantage? Evidence from the New Zealand Census-Mortality Study

To examine all-cause mortality differentials among New Zealand's (NZ) immigrant population. Unlike other studies that use the total non-migrant population as the reference group, we use NZ-born populations of the same ethnic group for comparison purposes. Our study intends to answer two questions: first, do immigrants have a mortality advantage relative to their NZ-born counterparts of the same ethnicity? Second, does an immigrant mortality advantage, if one exists, decline as duration of residence increases?

Data from the New Zealand Census-Mortality Study from 1996-1999 and 2001-2004 were used. The main variable of interest, years of residence in NZ, was classified as living in NZ for less than 5, 5-9, 10-19, 20-34, 35 or more years, and born in NZ. Three main ethnic groups were examined, such as Asian, Pacific, and European/Other. Mortality rates for subgroups within these broad ethnic groups were not calculated. Negative binomial models controlled for socioeconomic and demographic factors to assess the independent effect of duration of residence on mortality.

European/Other and Asian immigrants have a mortality advantage relative to their NZ-born counterparts, which declines as length of residence increases. Within strata of duration of residence, there are few differences between European/Other and Asian mortality. Pacific immigrants showed no statistically significant mortality advantage relative to the NZ-born Pacific people, and had higher mortality rates than Europeans/Others or Asians regardless of duration in NZ.

Findings from our study are consistent with international literature. Both the healthy migrant effect and acculturation may be responsible for the protective mortality effect among Asians and Europeans/Others that erodes over time. However, our results for the Pacific population suggest some migrant groups come to the host country with a health disadvantage and with no apparent healthy migrant effect.