The sample used in this study derives from Wave 1 and Wave 2 (separated by twelve months) of the National Longitudinal Study of Adolescent Health (Add Health; Resnick et al., 1997). The Add Health study was established to determine the causes of health-related behaviours of adolescents and their outcomes in young adulthood. A sample of 80 high schools and 52 middle schools from the US was selected with unequal probability of selection. Incorporating systematic sampling methods and implicit stratification into the Add Health study design ensured this sample is representative of US schools with respect to region of country, urbanicity, school size, school type, and ethnicity (Resnick et al., 1997). Adolescents were randomly selected to take part in in-home interviews at two time points separated by twelve months (1995 response rate, 78.9% & 1996 response rate, 88.2%). Data were collected using computer assisted interview which yields higher reported prevalence of risk-taking behaviour than regular interviews (Resnick et al., 1997). Sensitive questions, including those on pubertal development and substance use were given via headphones. Audio presentation of items relating to risk-taking
