The authors of this New Zealand case study state that the difference in mortality between current and never-smokers varies over time, affecting future projections of health gains from tobacco control. They used New Zealand census data to examine this heterogeneity by sex, ethnicity and cause of death on absolute and relative scales. The data included smoking status, which the researchers linked to subsequent mortality records for 25–74-year olds over 3 time periods spanning 30 years: 1981–84; 1996–99; and 2006–11. The analysis yielded 16.1 million personyears of follow-up. Age-standardised mortality rates and rate differences (SRDs) were calculated for current and never-smokers. The analysis identified a decline in mortality over time in never-smokers, whereas mortality trends varied by sex, ethnicity and cause of death among current smokers. SRDs were stable over time in European/Other men, moderately widened in European/Other women and markedly increased in Māori men and women. In Poisson regression analyses adjusting for multiple socioeconomic factors and household smoking, smoking-mortality rate ratios (RRs) increased from 1981–84 to 1996–99 and there was a moderate increase from 1996–99 through to 2006–11 (RRs of 1.48, 1.77, 1.79 in men and 1.51, 1.80, 1.90 in women, respectively). Socioeconomic confounding also increased over time.
