Results are displayed in Table 2. About 81% of the sample had ever had a drink, and the mean age of first drink was 15.7 years (SD=2.56). Parental AUD, whether defined by 1- or 2-affected parents, significantly increased the hazard of initiating alcohol use by 16-22% over that for no affected parents, and this effect did not vary by risk period. In contrast, for several risk factors, violations of the proportional hazards assumption were observed, requiring interactions that modeled differential hazard coefficients across age periods. Two were associated with significant increases in the hazards of initiating alcohol use before age 13; ever-use of cannabis was associated with an 852% increase, and parental separation was associated with an 84% increase. Ever-use of cannabis increased the hazard of initiation at other age periods as well. Nonassaultive trauma, externalizing disorders and perceived peer substance use significantly increased the hazards of alcohol initiation before age 16 by 15%, 53% and 145% respectively. Perceived peer substance use also increased the hazard by 60% from age 16-18, but not thereafter.
