Peer group deviance was assessed by two validated instruments (Johnston et al. 1982; Tarter & Hegedus, 1991) that evaluated the proportion of the respondent’s friends, at ages 12–14, 15–17, 18–21 and 22–25, who were engaged in a range of deviant behaviors (MM3) (see Kendler et al. 2007 for details). Test–retest reliability (ICC) was, for the four age groups, +0.75, +0.81, +0.78 and +0.73 respectively. Alcohol availability was assessed by a single item from the Monitoring the Future study (Johnston et al. 1982), which asked subjects at ages 12–14, 15–17 and 18–21, on a four-point scale, how easy it would have been to get alcohol if they wanted to use it. Reliability (ICC) of this item at these three time periods was +0.65, +0.70 and +0.62 respectively.
