These researchers aimed to determine whether parental smoking is a consistent risk factor for adolescent smoking, and whether maternal and paternal effects combine additively or multiplicatively, by examining data from annual national cross-sectional surveys (2002–2004 combined) with a multi-ethnic sample of 91,219 Year 10 students from New Zealand who answered a questionnaire on personal and parental smoking. The results showed that maternal smoking and paternal smoking were associated separately with an increased risk of daily adolescent smoking in all ethnic groups except paternal smoking in Asian youth. In each ethnic group, after adjusting for age and sex, the relative risk of adolescent daily smoking was significantly higher for maternal only smoking compared with paternal only smoking: Asians 5.50 (95% CI 3.55 to 8.52), Europeans 1.38 (1.26 to 1.52), Pacific Islanders 1.38 (1.10 to 1.73), and Mäori 1.10 (1.00 to 1.21). The excess maternal effect varied inversely with smoking prevalence. The net effects of maternal and parental smoking were additive for European, Mäori, and Pacific Island students, but multiplicative in Asian. Overall, about 40% of adolescent daily smokers could be attributed to parental smoking.
