Table 2 presents the mean TLI scores of participants, clustered according to temporal order of alcohol and cannabis use initiation. As illustrated, the most severe TLI scores were obtained by youths whose first substance was cannabis. Indeed, the TLI score is 7 times higher than youths whose consumption began with alcohol and 1.5 times higher in youths who began using alcohol and cannabis during the same month. Complementing these findings, the hazard rate related to age of first alcohol use increases by 11% (HR = 1.11, p = .04, 95% CI [1.002, 1.23]) for each standard deviation increase in TLI severity compared with 24% for cannabis use (HR = 1.24, p = .007, 95% CI [1.06, 1.45]). In practical terms, each standard deviation increase in TLI corresponds to lowering the age of alcohol use onset by 3.2 months (95% CI [−5.47, .45]) and cannabis use onset by 4.6 months (95% CI [−7.40, −1.69]).
