The method of analysis employed in the present study facilitated examination of the relationship and degree of overlap between the liabilities to initiation and progression of substance use. Differences were observed between alcohol use and cigarette and marijuana use. The relationship between alcohol initiation and heavy/problem use was found to be moderate in magnitude (range of beta coefficients: 0.48–0.65). Overall, the results concur with findings from previous twin studies in adults [17], suggesting separate but related liabilities for initiation of use and frequency of alcohol use.
