What is the contribution of smoking and socioeconomic position to ethnic inequalities in mortality in New Zealand?

Background Mortality rates for Maori are twice those for non-Maori in New Zealand. We have assessed the contribution of tobacco smoking and socioeconomic position to these inequalities in 45-74-year-old census respondents during 1981-84 and 1996-99 (2.3 and 2.7 million person-years, respectively). Methods We used linked census and mortality cohort datasets with measures of socioeconomic position (household income, highest educational qualification, car access, labour-force status, and neighbourhood deprivation) and smoking (never, ex, current). We used direct standardisation to adjust for smoking and Poisson regression to adjust for socioeconomic position. Findings The apparent contribution of smoking to mortality differences between Maori and non-Maori non-Pacific people was greatest for women in 1996-99 (8% reduction in standardised rate difference); it had increased from 3% in 1981-84. The corresponding reductions in men were 5% in 1996-99 and -1% in 1981-84. The apparent contribution of socioeconomic factors to mortality differences between Maori and non-Maori non-Pacific was greatest for men (39% in 1981-84 and 37% in 1996-99) and increased over time for women (from 23% in 1981-84 to 32% in 1996-99). Interpretation Although small, the contribution of smoking to ethnic inequalities in mortality increased over time and might grow more during the next two decades if differences in smoking between ethnic groups continue to increase. Better measurement of socioeconomic position (eg, lifecourse measures, asset wealth) might increase the proportion of ethnic inequalities attributable to socioeconomic position, perhaps to about half Action to redress socioeconomic gaps and control of tobacco use will both be important in reducing ethnic inequalities in health.