METHODS
Data for the current study were collected as part of Youth’12, a nationally representative survey of the health and well-being of secondary school students in New Zealand. In total, 8,500 secondary school students participated, representing 3% of the total population of all secondary school students in New Zealand. There were slightly more females
(54%) than males and slightly more younger students (22% aged # 13 years, 22% aged 14 years, and 21% aged 15 years) than older students (19% aged 16 years and 17% aged $ 17 years). Full details of the methodology and design of the Youth’12 survey have been described previously