Exposure to already-onset peers (H2) was also a highly significant predictor of onset to drinking (t(9) = 5.13, p < .001) and, like the selection effect, did not vary significantly across schools from the pooled mean effect of 1.39. This effect describes a hazard ratio of e1.39 = 4.01 that differentiates the probability of onset for a student with no drinkers as friends from a student with only drinkers as friends (a unit increase in the proportion of drinking friends). In addition, the hazard rate for first alcohol onset increased with each grade by about e0.14 = 15%, reflecting accelerating onset from grades 6–8. The hazard rate for onset was also associated (t(11) = 15.1, p < .001) with the amount of student-reported adult supervision when with friends (H7). Rate of onset was about four times greater for youth reporting 30 days of unsupervised time with friends in the previous month, compared to those reporting none. These effects did not vary across schools; standard deviation χ2 statistics were all nonsignificant.
