Does mortality vary between Asian subgroups in New Zealand: an application of hierarchical Bayesian modelling.

The aim of this paper was to see whether all-cause and cause-specific mortality rates vary between Asian ethnic subgroups, and whether overseas born Asian subgroup mortality rate ratios varied by nativity and duration of residence. We used hierarchical Bayesian methods to allow for sparse data in the analysis of linked census-mortality data for 25-75 year old New Zealanders. We found directly standardised posterior all-cause and cardiovascular mortality rates were highest for the Indian ethnic group, significantly so when compared with those of Chinese ethnicity. In contrast, cancer mortality rates were lowest for ethnic Indians. Asian overseas born subgroups have about 70% of the mortality rate of their New Zealand born Asian counterparts, a result that showed little variation by Asian subgroup or cause of death. Within the overseas born population, all-cause mortality rates for migrants living 0-9 years in New Zealand were about 60% of the mortality rate of those living more than 25 years in New Zealand regardless of ethnicity. The corresponding figure for cardiovascular mortality rates was 50%. However, while Chinese cancer mortality rates increased with duration of residence, Indian and Other Asian cancer mortality rates did not. Future research on the mechanisms of worsening of health with increased time spent in the host country is required to improve the understanding of the process, and would assist the policy-makers and health planners.

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

OBJECTIVE: 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? DESIGN: 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. RESULTS: 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. CONCLUSION: 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.