Trends in survival and life expectancy by ethnicity, income and smoking in New Zealand: 1980s to 2000s

Abstract

Background: Survival and life expectancy are commonly used metrics to describe population health. There are two objectives to this paper: (1) to provide an explanation of methods and data used to develop New Zealand life-tables by ethnic, income and smoking groups; and (2) to compare cumulative survival and life expectancy trends in these subpopulations.

Method: We generated sex-specific life-tables for seven subpopulations: ethnicity (Maori and non-Maori); income tertiles; smoking (never and current); and two-way combinations (ethnicity by income; ethnicity by smoking; and smoking by income). This was repeated for five census-mortality cohorts (1981-84, 1986-89, 1991-94, 1996-99, and 2001-04). The method used to create the life-tables brings together three pieces of information: (1) the official Statistics New Zealand (SNZ) life-tables by year and sex; (2) the proportionate distribution of the total population by subpopulation (e.g. smoking prevalence); and (3) estimates of the differences in subpopulation mortality rates (from the New Zealand Census-Mortality Study [NZCMS]).

Results: Survival and life expectancy improved in all subpopulations across the five census cohorts. However, improvements were greater in non-Maori compared to Maori and high income compared to low income subpopulations. This led to widening of the gap in life expectancy between 1981 and 2001 between Maori and non-Maori (males), which increased from 5.4 years in 1981 to 9.0 in 2001 and between low income and high income which increased from 4.4 in 1981 to 6.5 in 2001 for males. The gap in life expectancy between current and never smokers in 1996 was 7.6 in males and 6.7 in females. However, the size of this gap varied by ethnicity: 7.3 and 6.2 for non-Maori males and females, and 4.3 and 3.9 for Maori male and females. Correspondingly, the gap in life expectancy between Maori and non-Maori is greater among never smokers (9.7 and 8.4 for males and females) than among current smokers (4.3 and 6.6 for males and females).

Conclusion: Life-tables have been successfully developed for subpopulations in New Zealand, and provide an alternative understanding of health and life in New Zealand over the past 20 years. Ethnic and income gaps in life expectancy have widened, and perhaps surprising results were found for smoking by ethnicity. These life-tables provide an important basis for subpopulation modelling and projections, and are freely available to researchers.