Jude Ball, Dalice Sim, Richard Edwards

Smoking among New Zealand (NZ) adolescents has declined since 2000, but ethnic disparities remain pronounced. To inform prevention efforts, we investigated exposure to and relative importance of known predictors of adolescent smoking and how these have changed over time, for Māori (NZ's indigenous population) and adolescents overall. We used repeat cross-sectional data, 2003 to 2015, from a national survey of 14- to 15-year-olds (N=20,443 to 31,696 per year). For the overall sample and for Māori and non-Māori we calculated adjusted odds ratios (aOR) to assess the association between regular smoking and risk factors each year: one or more parents smoke, best friend smokes, older sibling(s) smoke, and past week exposure to smoking in the home. We calculated population attributable risk (PAR) for risk factors in 2003 and 2015. Between 2003 and 2015 aOR for exposure to smoking in the home increased from 1.7 (95% CI 1.6, 1.8) to 2.6 (2.1, 3.1) overall, and from 1.8 (1.6, 2.1) to 3.4 (2.5, 4.5) for Māori; aOR for 'best friend smokes' also increased, while aORs for sibling smoking and parental smoking did not change meaningfully. PAR for exposure to smoking in the home increased from 17% to 31% overall, and from 28% to 57% for Māori, while PARs for other risk factors decreased. Exposure to smoking in the home has become more strongly associated with adolescent smoking over time and is an increasingly important risk factor at the population level (independent of parental smoking), particularly for Māori.